A Systematic Review of Acculturation and Sleep Health Among Adult Immigrants in the United States

Abstract

The United States (U.S.) has more immigrants than any other country in the world, with an estimated 44 million non-U.S.-born individuals residing in the country as of 2018. Previous studies have linked U.S. acculturation to both positive and negative health outcomes, including sleep. However, the relationship between U.S. acculturation and sleep health is not well understood. This systematic review aims to identify and synthesize scientific studies on acculturation and sleep health among adult immigrants in the U.S. A systematic search of the literature was performed in PubMed, Ovid MEDLINE, and Web of Science in 2021 and 2022 with no date limiters. Quantitative studies published anytime in a peer-reviewed journal in English among an adult immigrant population with an explicit measure of acculturation and a sleep health dimension, sleep disorder, or daytime sleepiness measure were considered for inclusion. The initial literature search yielded 804 articles for review; after removing duplicates, applying inclusion and exclusion criteria, and searching reference lists, 38 total articles were included. We found consistent evidence that acculturative stress was associated with worse sleep quality/continuity, daytime sleepiness, and sleep disorders. However, we discovered limited consensus on the association of acculturation scales and acculturation proxy measures with sleep. Our review demonstrated that compared to U.S.-born adult populations, there is a high prevalence of adverse sleep health among immigrant populations, and acculturation likely plays an important role in shaping this disparity, particularly through acculturative stress.

Introduction

Sleep health, characterized by multiple dimensions including satisfaction, appropriate timing, adequate duration, efficiency, and sustained alertness during waking hours, is an integral component of physical and mental wellbeing [1]. Poor sleep quality and short sleep duration (less than seven hours of sleep) are risk factors for a multitude of chronic diseases, including hypertension, diabetes, and obesity, as well as all-cause mortality [2,3]. Sleep health and sleep disorders are not equally distributed among racial and ethnic groups in the United States (U.S.) [4]. A review of the sleep disparities literature has shown that, in general, Asian, Black, Hispanic/Latino, and Native Hawaiian and Pacific Islander groups in the U.S. have shorter sleep duration and worse sleep quality, both objectively measured and self-reported, than their White counterparts [4]. Growing evidence suggests that sleep health disparities may fundamentally contribute to racial/ethnic health disparities in general, particularly disparities in cardiovascular health [3,5].

Socioecological conceptual models describe an interplay of societal, neighborhood/environmental, familial/household, and individual level factors that contribute to disparities in sleep health [5–7]. These levels, from the individual level up to the societal level, interact with and influence one another over time to exert a cumulative impact on sleep health, ultimately shaping health disparities [7]. The U.S. immigrant community is particularly vulnerable to the multifactorial determinants of sleep health disparities due to factors such as lower socioeconomic status, lower health insurance coverage rates, language barriers, social isolation, and immigration-related anxiety [8]. For example, societal factors, like segregation of immigrant groups within the labor market into lower-wage and lower-skilled jobs, can lead to unequal exposure to work-related stressors and hazards [9]. An ancillary study from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) demonstrated that Hispanic/Latino adults employed in rotating and nightshift work had reduced sleep duration and sleep efficiency compared to those in day work and other types of work schedules [10]. Additionally, unfavorable neighborhood characteristics, such as artificial light, safety, noise, traffic, and pollution, are inequitably distributed among historically minoritized Black and immigrant communities due to lasting structures from historically racist policies such as segregation and redlining, and can negatively impact sleep health [7,11]. Other neighborhood characteristics such as neighborhood social cohesion and neighborhood ethnic composition can also influence sleep health in immigrant communities. For example, a study of Hispanic/Latino immigrants showed that those with low neighborhood social cohesion were significantly less likely to report sleeping the recommended amount compared to those with high social cohesion [12]. Familial/household level factors, such as immigrant generation, familism, and cultural sleep-related beliefs, attitudes, and practices play a key role in shaping home environments that influence sleep [13]. Lastly, on the individual level, psychosocial stressors such as interpersonal discrimination based on race/ethnicity has been associated with shorter sleep duration and daytime sleepiness among Hispanic immigrant groups [14]. Similarly, other psychosocial stressors, like English language anxiety, have been associated with higher insomnia prevalence among Asian immigrant groups [15].

Despite these documented sleep health disparities among racial/ethnic minorities and immigrant populations, sleep health research among immigrant populations remains limited. The small number of studies evaluating sleep, among mostly Hispanic immigrants, have generally found a phenomenon known as the “Hispanic Paradox,” where Hispanic individuals tend to have better health outcomes compared to their U.S.-born counterparts, despite being more socioeconomically disadvantaged [16–18]. However, this association is not consistent. Other studies have found little to no difference in sleep duration between Hispanic immigrants and their U.S.-born counterparts after adjusting for sociodemographic characteristics, depression, anxiety, and perceived stress [19]. Conversely, some studies have shown that certain Hispanic immigrant groups, such as non-U.S.-born Dominicans, Cubans, Central/South Americans had greater odds of short sleep duration than their U.S.-born counterparts [20]. Among other racial groups, a study by Jackson et al. using a nationally representative sample of U.S. adults from the 2004-2011 National Health Interview Survey (NHIS) found that non-U.S.-born Black immigrant workers had a higher prevalence of short sleep than U.S.-born Black workers and that the Black-White disparity was larger for non-U.S.-born Black immigrants than for their U.S.-born counterparts [9]. However, similar to the mixed results observed for Hispanic immigrants, there are other studies that have found, for example, that U.S.-born Black Caribbean Americans in fact reported less sleep complaints than their non-U.S.-born counterparts [21]. Lastly, another study using 2012 NHIS data found that the age-adjusted prevalence of short sleep duration did not vary significantly between non-U.S. and U.S.-born Black Americans, although the prevalence did vary for Hispanic (34.3% U.S.-born vs. 26.7% non-U.S.-born) and Asian (38.2% U.S.-born vs. 27.9% non-U.S.-born) adults [22]. Due to these mixed findings, more research is needed to elucidate the theoretical mechanisms, such as acculturation, through which immigrant populations may be at a sleep health advantage or disadvantage.

Acculturation, broadly described as the process by which individuals adopt the attitudes, values, customs, beliefs, and behaviors of another culture, [23] is an important component of understanding immigrant health, including sleep health. Williams et al. describe the importance of culture in sleep research, as sleep is a “socially scheduled and culturally institutionalized as well as practiced with different meaning across racial, ethnic, cultural, and religious groups” [24]. For example, Latin American and Caribbean cultures endorse a biphasic sleep modality, where a short sleep is practiced midday, with longer sleep duration at night [24]. Certain Asian communities, such as the Hmong, maintain cultural beliefs around sleep such as “dab tsog,” the belief of a frightening night spirit pressing on their chest, which has been associated with sleep apnea indicators, sleep paralysis, nightmares, hypnogogic hallucinations, and insomnia [25]. However, the effect of adaptation to U.S. culture on the health of immigrant populations is complex and has been associated with both positive and negative sleep health [26]. For example, several studies of Hispanic individuals have suggested “negative acculturation,” where higher degrees of U.S. acculturation among Mexican-born immigrants was associated with shorter sleep durations [27,28]. However, this association is complex and may be different for diverse Hispanic groups [18], ages [29], and socioeconomic statuses [16,30]. Therefore, while U.S. acculturation is likely an important determinant of sleep health among immigrant populations, the theoretical mechanisms are not well understood. There are several theorized explanatory pathways between acculturation and sleep health. U.S. acculturation has been linked to changes in health-related behaviors, such as increased alcohol consumption, which can disrupt sleep-related physiology with chronic use [31,32]. Alternatively, prolonged activation of stress response systems due to chronic acculturative stress, or the psychological impact and stress reaction of adapting to a new cultural context [31], can influence depression, anxiety, and maladaptive behaviors, or can upregulate the hypothalamic-pituitary-adrenal axis and sympathetic nervous system, all of which have been associated with worse sleep health and disorders [31].

In order to better understand sleep health disparities in immigrant populations, it is crucial to systematically evaluate existing studies of acculturation and sleep and identify gaps and limitations to leverage in future research. Although summaries and scoping reviews of sleep health among immigrant populations exist [31,33], to our best knowledge, no systematic review to date has summarized all of the existing health literature on explicit measures of acculturation and sleep health and disorders among U.S. immigrants. Therefore, the aim of this paper was to identify and synthesize scientific studies on acculturation and sleep health or sleep disorders among adult immigrants in the U.S. Specifically, we sought to understand how different measurements of acculturation, including acculturation scales, acculturative stress, and acculturation proxies, were associated with various sleep health outcomes, including sleep duration/timing, sleep quality/continuity, daytime sleepiness, and sleep disorders.

Methods

Search strategy

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [34]. First, a limited search of PubMed with the initial search string “(acculturation OR immigrant) AND (sleep)” was conducted to identify relevant keywords contained in the title, abstract, and subject descriptors. Additional terms and the synonyms used by respective databases identified in this way (“foreign-born,” “non-U.S.-born,” and “assimilation”) were used in an extensive search of the literature in PubMed, Ovid MEDLINE, and Web of Science on February 8^th, 2021. No date limiters were used, and any study that met the inclusion criteria, regardless of publication date, was considered for inclusion. Reference lists of the articles collected from stage two were manually searched to identify any additional studies of interest. An updated search of the literature was conducted on February 22^nd, 2022.

Inclusion and exclusion criteria

Quantitative studies published in a peer-reviewed journal in English were considered for inclusion. Inclusion criteria consisted of immigrant adults (18 years or older) who were born outside of the U.S. and were the first generation in their family to reside in the U.S. (1^st generation immigrants) or who were identified as part of the immigrant community (i.e., 2^nd generation immigrants, or children of non-U.S.-born 1^st generation immigrants). Research suggests that acculturation levels change from adolescence to adulthood [35], therefore the present study focused on acculturation and sleep among adults only and excluded studies among children and adolescents (n=3). Only studies with both a measure of acculturation, the exposure of interest, and a dimension of sleep health, a sleep disorder, or a measure of daytime sleepiness were included. The sleep disorders category included clinically diagnosed disorders, self-reported diagnoses, or disorders assessed via validated scales. Because the measurement of acculturation can range from proxy variables (e.g., country of birth) to validated acculturation questionnaires, only studies that explicitly indicated that their measure was intended to approximate acculturation were included.

Data collection

Records obtained from the searches detailed above were managed in Zotero and Covidence [36]. Applying the inclusion and exclusion criteria to the retrieved articles, one reviewer (J.A.) examined the titles and abstracts to determine eligibility for full-text review. Two reviewers (J.A., K.W.) independently assessed the eligibility of the full-text articles. Discrepancies in reviewer selections were deliberated at meetings between all reviewers (J.A., K.W., D.J.) until a final consensus was reached.

Data extraction

Extraction categories were pre-determined at a meeting between two reviewers (J.A., D.J.). Two reviewers (J.A., K.W.) independently extracted data from the full-text articles into an Excel sheet. Discrepancies in extractions were deliberated at a meeting between all reviewers (J.A., K.W., D.J.) until a final consensus was reached.

Assessment of study quality

The methodological quality of the articles was assessed with the National Heart, Lung, and Blood Institute (NHLBI)’s “Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies” [37]. Two reviewers (J.A., K.W.) independently evaluated the studies on fourteen criteria, assigning one point for each criteria met, for a total score between 0 and 14. Based on the quantitative total score, each study was given a qualitative quality rating of “Good” (score of 10-14), “Fair” (score of 5-9), or “Poor” (score of 0-4). Discrepancies in quality ratings were deliberated at a meeting between all reviewers (J.A., K.W., D.J.) until a final consensus was reached.

Results

The database searches resulted in 804 initial records (Figure 1). After removal of 321 duplicate records, 483 remained for title and abstract screening. Irrelevant records were excluded, and 64 records were assessed for full-text eligibility. Of the full-text studies, 14 were excluded for having no explicit measure of acculturation, 11 were excluded for not being a peer-reviewed manuscript, 3 were excluded for having non-quantitative results, 3 were excluded for having no sleep outcome, and 3 were excluded for having non-adult participants, yielding 30 studies for inclusion in the review. We manually reviewed 1,574 citations included in the reference lists of these 30 studies, and identified one additional study for inclusion, for a total number of 31 studies. Finally, an additional 7 studies were identified through the updated search conducted on February 22^nd, 2022, yielding the total number included in this synthesis of 38 studies.

Figure 1.

PRISMA flow diagram detailing the database searches, the number of abstracts screened, and the full texts retrieved for inclusion in the qualitative synthesis of this systematic review on acculturation and sleep health and sleep disorders in adult immigrant populations in the United States.

Study and participant characteristics

The study and participant characteristics are presented in Table 1. The included studies were published between 1999 and 2022, with the majority of the studies published in the past ten years. Two studies had a longitudinal study design, while the remaining were cross-sectional. Sample sizes ranged from n=30 participants to n=303,204 participants. Most of the studies included immigrants from Central or South America (n=23), followed by studies that included immigrants from Asia (n=10).

Table 1.

Characteristics of quantitative studies included in a systematic review on acculturation and sleep health and sleep disorders in adult immigrant populations in the United States (n=38).

Study Characteristics	Number of Studies (n=38)
Study Design
Cross-sectional	36
Longitudinal	2
Publication Year
Prior to 2000	1
2000 to 2011	6
2012 to 2022	31
Immigrant Region of Origin
Central or South America	23
Asia	10
Unspecifieda	5
Acculturation Measure b
Acculturation scales	18
Acculturative stress	7
Proxy variables (e.g., country of birth, length of residence)	15
Sleep Measure b
Sleep duration / timing	22
Sleep quality / sleep continuity	20
Daytime sleepiness	5
Sleep disorders (e.g., insomnia, sleep apnea, restless leg syndrome)	13
Other	1
Sleep Measurement Method
Subjective measures only (e.g., questionnaires, sleep diaries)	36
At least one objective measure (e.g., polysomnography, actigraphy)	2

^aMultiple countries of origin, or not specified

^bNumber of studies exceeds total as more than one category is possible

Table 2 summarizes the 38 included studies, outlining the study author’s name, study design, study population and sample size, acculturation measurement, sleep outcome and measurement, and results. The results column additionally contains arrows that refer to evidence of positive or negative acculturation: ↑ indicates positive acculturation, or that U.S. acculturation is beneficial to the sleep outcome; ↓ indicates negative acculturation, or that U.S. acculturation is harmful to the sleep outcome; → indicates no association between U.S. acculturation and the sleep outcome.

Table 2.

Summary of systematic review on acculturation and sleep health and sleep disorders in adult immigrant populations in the United States by measure of acculturation.

Study and Designa	Study Population (n)	Acculturation Measure	Sleep Outcome	Study Resultsb
1. Acculturation Scales
Song et al. 2022 [45] Cross-sectional	Older Korean immigrants living in two large predominantly Korean communities in southern California (n=43)	1) SAS-K: 12-item tool based on the SASH measuring language use, media, and ethnic social relations	1) Sleep quality: PSQI, 19-item questionnaire designed to measure self-reported sleep quality during the previous month	→ No significant differences in sleep quality by acculturation level
Barajas-Gonzalez et al. 2021 [47] Cross-sectional	Bangladeshi immigrant parents living in New York City (n=73)	1) Abbreviated Multidimensional Acculturation Scale: measure of English competence assessed using the language competence subscale	1) Sleep problems: PROMIS, measuring sleep disturbances over the past seven days	↑ Increase in parental English competence was associated with a decrease in reported sleep problems (β=−0.78, SE=0.33)
González et al. 2021 [48] Cross-sectional	Hispanic/Latino adults with moderate to severe OSA in four major metropolitan areas (Bronx, NY; Chicago, IL; Miami, FL; and San Diego, CA) as part of HCHS/SOL (n=1,605)	1) SASH: 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations	1) Sleep phenotype class: three latent classes (minimally symptomatic, excessive sleepiness, disturbed sleep) of five common OSA symptoms and four comorbidities	↓ Minimally symptomatic class, vs. excessive sleepiness and disturbed sleep classes, was the least acculturated group
Ghani et al. 2020 [42] Cross-sectional	Mexican adults living along the U.S.-Mexico border (n=100)	1) ARSMA-II: measure of language use and ethnic identity and interaction comprised of a 17-item questionnaire on Mexican cultural orientation and a 13-item questionnaire on Anglo cultural orientation	1) Insomnia: ISI, a 7-item instrument which assesses the nature, severity, and impact of insomnia 2) Daytime sleepiness: ESS, an 8-item questionnaire that asks respondents to rate their likelihood of falling asleep in eight different contexts 3) Sleep quality: PSQI, 19-item questionnaire designed to measure self-reported sleep quality during the previous month 4) Sleep duration: Sleep Timing Questionnaire (STQ), a questionnaire to assess weekday and weekend sleep duration and validated against a prospective sleep diary 5) Sleep efficiency: weekday and weekend sleep efficiency calculated from values in the STQ 6) Sleep apnea risk: assessed using the Multivariable Apnea Prediction index	→ No associations between Mexican acculturation and any of the sleep outcomes ↓ Increasing levels of Anglo acculturation was associated with less sleep on weekends (β=−41.07, 95% CI: −73.6, −58.49), lower weekend sleep efficiency (β=−4.26, 95% CI: −7.09, −1.43), worse sleep quality (β=1.13, 95% CI: 0.42-1.84), more insomnia (β=1.32, 95% CI: 0.44-2.20), and increased risk for sleep apnea (β=5.57. 95% CI: 1.64-9.49) in models that adjusted for age, sex, and education
Karan and Park 2020 [77] Cross-sectional	Chinese and Korean international college students in the U.S. (n=266)	1) Multigroup Ethnic Identity Measure (MEIM): 12-item questionnaire adapted from the full MEIM assessing a sense of membership and feelings toward ethnicity and ethnic identity 2) American Identity Measure: 12-item questionnaire adapted from the full MEIM assessing sense of membership and feelings toward the U.S.	1) Sleep quality: PSQI, 19-item questionnaire designed to measure self-reported sleep quality during the previous month	↓ Compared to marginal orientation, bicultural (aOR=0.44, β=−0.81, SE=0.38) and Asian orientation (aOR=0.40, β=−0.91, SE=0.39) were associated with better sleep quality in models that adjusted for sex, school year, SES, and country of birth → No association between American orientation and sleep quality
Gonzalez and Lu 2018 [63] Cross-sectional	Chinese breast cancer survivors throughout the U.S. (n=80)	1) Stephenson Multigroup Acculturation Scale (SMAS): 32-item questionnaire to measure ethnic society immersion and dominant society immersion	1) Sleep quality: Chinese version of the PSQI, a 19-item questionnaire designed to measure self-reported sleep quality during the previous month	→ Mean acculturation score for participants with a total PSQI score <5 was not meaningfully different than the mean acculturation score for participants with a PSQI score ≥5
Martinez-Miller et al. 2018 [43] Cross-sectional	Hispanic/Latino adults in the Sacramento Valley region of California as part of the Sacramento Area Latino Study on Aging (SALSA) and the Niños Lifestyle and Diabetes Study (NLDS) (n=2,386)	1) ARSMA-II: measure of language use and ethnic identity and interaction comprised of a 17-item questionnaire on Mexican cultural orientation and a 13-item questionnaire on Anglo cultural orientation	1) Sleep class: latent class of overall sleep comprised of self-reported restless sleep, general fatigue, waking up far too early, trouble falling asleep, and waking up several times a night 2) Restless sleep: self-reported restless sleep extracted from the Center for Epidemiological Studies Depression Scale 3) Sleep duration (sub-sample only): self-reported average hours of sleep, computed as the weighted average of weekday and weekend sleep 4) Sleep apnea (sub-sample only): self-reported medical diagnosis of sleep apnea	↑ First-generation older Latinos with high US acculturation, vs. high acculturation towards another origin/ancestral country, had less restless sleep (PR=0.67, 95% CI: 0.54-0.84) and a higher likelihood of being in the best sleep class than the worst (OR=1.62, 95% CI: 1.09-2.40) ↓ Second-generation participants with stable-high intergenerational U.S. acculturation had a higher prevalence of short sleep duration than participants with low intergenerational acculturation (PR=2.86, 95% CI: 1.02-7.99)
Im et al. 2017 [50] Cross-sectional	Multi-ethnic midlife women (40 to 60 years old) throughout the U.S. (n=1,054)	1) Suinn-Lew Asian Self-Identity Acculturation Scale (SL-ASIA): 21-item measure based on the ARSMA used to assess acculturation in Asian populations by assessing preferences for food, music, customs, language, and close friends	1) Sleep symptoms: using the Sleep Index for Midlife Women, a measure of sleep-related symptoms, such as sleep disorders, chronic pain, mood disorders, and vasomotor symptoms	→ In models that controlled for sociodemographic characteristics and menopausal status, only self-reported racial/ethnic identity (rather than immigration status, the level of acculturation, or the length of stay in the U.S.) was associated with sleep-related symptoms ↓ For race/ethnicity stratified models, Hispanic women who were immigrants, stayed longer in the U.S., and were more acculturated tended to report more sleep-related symptoms and a higher total severity → Immigration variables were not related to sleep-related symptoms in other race/ethnicity groups
Zeiders et al. 2017 [38] Longitudinal	Mexican and Mexican American young adults in Southwest U.S. (n=246)	1) ARSMA-II: established measure of language use and ethnic identity and interaction comprised of a 17-item questionnaire on Mexican cultural orientation and a 13-item questionnaire on Anglo cultural orientation	1) Sleep duration: using the 7-day phone protocol, the self-reported mean time in between reported bedtime and wake time across seven calls 2) Sleep variability: using standard regression, how much each individual varied from their own overall average sleep duration sleep	→ Bicultural (high Anglo-high Mexican) and enculturated orientation (low Anglo-high Mexican) reported no association between discrimination and sleep duration ↓ Acculturated orientation (high Anglo-low Mexican) reported a negative association between discrimination and sleep duration and marginalized orientation (low Anglo-low Mexican) reported a positive association
D’anna-Hernandez et al. 2016 [39] Longitudinal	Pregnant Mexican American adult women in an urban U.S. city (n=60)	1) SASH: 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations	1) Sleep duration: reported bed and wake times and total hours of sleep via a sleep diaries on three consecutive days at each phase 2) Sleep onset: minutes to fall asleep via sleep diary 3) Sleep disruptions: times woke during the night via sleep diary 4) Feeling refreshed upon waking: rated 1 (extremely tired) to 7 (extremely refreshed) in sleep diary	↓ In cross-sectional analyses, maternal acculturation was only associated with feeling refreshed upon waking (β=−0.36, SE=0.16) ↓ In longitudinal analyses, multilevel modeling revealed that women who were more acculturated reported more times up during the night and lower feelings of being refreshed upon awakening across pregnancy
Nuyen et al. 2016 [78] Cross-sectional	Hispanic/Latino adults in southern California (n=573)	1) Brief Acculturation Scale for Hispanics (BASH): a four-item language-based questionnaire adapted from the Short Acculturation Scale for Hispanics	1) Daytime sleepiness: ESS, an 8-item questionnaire that asks respondents to rate their likelihood of falling asleep in eight different contexts	→ Acculturation did not moderate the relationship between EDS and depression
Hale et al. 2014 [46] Cross-sectional	Multi-ethnic adult women in Oakland, CA, Los Angeles, CA, and Newark, NJ as part of SWAN (n=1,180)	1) SASH: 4-item adaption of the 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations, extended to other languages (Japanese, Chinese)	1) Sleep complaints: Four questions about sleep complaints in the past two weeks (difficulty falling asleep, awakenings, difficulty returning to sleep, and typical sleep quality) adapted from the Women’s Health Initiative Insomnia Rating Scale (WHIIRS)	↓ Language acculturation or unmeasured factors associated with language acculturation mediated 40.4% (95% CI: 28.5%-69.8%) of the association between immigrant status and any sleep complaint
Sawanyawisuth et al. 2013 [49] Cross-sectional	Hispanic adults of Mexican descent and non-Hispanic White adults in San Diego County, CA as part of The Sleep Health and Knowledge in U.S. Hispanics Project (n=3,667)	1) SASH: 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations	1) Restless leg syndrome (RLS): diagnosed using patient-reported answers to the four essential criteria by the International Restless Legs Study Group	↓ Hispanic adults of Mexican descent with high acculturation had significantly higher RLS prevalence than those with low acculturation (17.4% vs. 12.8%, respectively)
Kachikis and Breitkopf 2012 [19] Cross-sectional	Hispanic/Latina, White/non-Hispanic, and Black/non-Hispanic adult women in southeast Texas (n=2,670)	1) SASH: 5-item adaption of the 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations	1) Sleep duration: self-reported average number of hours of sleep each night in the past month 2) Sleep quality: self-reported rating of overall quality of sleep on 5-point Likert scale 3) Sleep adequacy: self-reported frequency of feeling like one got the amount of sleep needed in the past month	→ No association between acculturation and sleep duration in models adjusted for sociodemographic characteristics, depression, anxiety, and perceived stress ↓ Higher acculturation was associated with poorer sleep quality in models adjusted for sociodemographic characteristics, depression, anxiety, and perceived stress (β=−0.06, SE=0.02) → No association between acculturation and sleep duration among the Hispanic sample (n=1,966) in models adjusted for sociodemographic characteristics, depression, anxiety, and perceived stress
Green et al. 2010 [44] Cross-sectional	Hispanic/Latino women in Newark, NJ as part of SWAN (n=419)	1) SASH: 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations	1) Sleep problems: Four questions assessing problems with sleep initiation, maintenance, early awakening, and overall quality in the past two weeks	→ No difference in the median sleep problem score between the low acculturation group (3.0, IQR: 0.0-6.0) and the high acculturation group (3.0, IQR: 0.0-5.0)
Cantero et al. 1999 [41] Cross-sectional	Hispanic/Latino women in Los Angeles, CA as part of the Proyecto a Su Salud study (n=573)	1) Cantero 1999 Measure: Created acculturation scale, adapted from ARSMA, that included an 11-item measure of language acculturation and length of residence in the U.S.	1) Sleep duration: self-reported average hours of sleep per night	→ No difference in the prevalence of short sleep duration between the low (53.4%), medium (54.5%), and high (53.4%) acculturation groups
2. Acculturative Stress Questionnaires
Lee et al. 2021 [52] Cross-sectional	Chinese and Korean Americans in the Washington, DC. Metropolitan Area (n=400)	1) HSI: 9-item occupational and emotional stress subscale of the HSI for use among Asian populations	1) Sleep disturbance: 8-item questionnaire from PROMIS to measure self-reported perceptions of sleep quality, depth, and restoration within the past seven days 2) Sleep duration: self-reported continuous value of sleep duration calculated from usual sleep and wake time in hours and minutes	↓ Greater acculturative stress was associated with a higher prevalence of sleep disturbance in Poisson models that adjusted for sociodemographic characteristics and chronic conditions (aPR=1.18, 95% CI: 1.06-1.31). Effect measure modification tests suggested that this association was only significant for women (aPR=1.30; 95% CI: 1.13-1.49) and those who identity as “very Asian” (aPR=1.21; 95% CI: 1.08-1.35) ↓ One-unit increase in acculturative stress was associated with 0.08 hr less sleep in linear models that adjusted for sociodemographic characteristics and chronic conditions (β=−0.08, SE=0.04)
Green et al. 2021 [17] Cross-sectional	First-generation Hispanic/Latinx immigrants in central Virginia (n=231)	1) Riverside Acculturation Stress Inventory (RASI): discrimination subscale of the RASI used to capture acculturative stress due to racial/ethnic discrimination	1) Sleep duration: self-reported average hours of sleep per night in a regular week 2) Difficulty falling asleep: self-reported rating of difficulty falling asleep during a regular week 3) Waking at night: self-reported number of awakenings falling asleep during a regular week 4) Difficulty going back to sleep: self-reported rating of difficulty going back to sleep during a regular week 5) Sleep quality: self-reported rating of general sleep quality based on a single survey question	↓ Nocturnal awakenings, fatigue, and self-reported sleep quality mediated approximately 13% of the total effect of perceived discrimination on self-reported physical health
Park et al. 2020 [51] Cross-sectional	Korean American adults throughout the U.S. (n=343)	1) Acculturative Stress Index: 17-item questionnaire with 6 subscales (homesickness, social isolation, employment barrier, discrimination, civic disengagement, and family problems) to evaluate acculturative stress	1) Sleep duration: self-reported average hours of sleep per night in the past month, computed as the weighted average of weekday and weekend sleep	↓ In women, higher homesickness (β = −23.19) and lower civic disengagement (β = 17.75) were associated with shorter sleep duration in models that adjusted for sociodemographic characteristics, comorbidities, sleep environment, and acculturation ↓ In men, higher isolation was associated with shorter sleep duration (β = −13.73)
Alcántara et al. 2019 [39] Cross-sectional	Hispanic/Latino adults in four major metropolitan areas (Bronx, NY; Chicago, IL; Miami, FL; and San Diego, CA) as part of HCHS/SOL (n=1,192)	1) HSI: abbreviated 17-item questionnaire that measures distress/worry associated with interpersonal, economic, and immigration conflict accompanying the process of adaptation and integration into a new nonnative culture within the past three months	1) Insomnia: ISI, a 7-item instrument which assesses the nature, severity, and impact of insomnia 2) Sleep duration: actigraphy-measured average duration of time scored as sleep between sleep onset and sleep offset across all days 3) Sleep efficiency: actigraphy-measured sleep duration divided by time between sleep onset and sleep offset averaged across all main sleep intervals 4) Sleep variability: SD of sleep duration across all days	↓ Greater acculturation stress was associated with greater insomnia symptoms, after adjusting for sociodemographic characteristics, health behaviors and conditions, and other stressors (ß=0.75, SE=0.26) → No consistent associations between acculturative stress and actigraphic sleep measures
Alcántara et al. 2017 [14] Cross-sectional	Hispanic/Latino adults in four major metropolitan areas (Bronx, NY; Chicago, IL; Miami, FL; and San Diego, CA) as part of HCHS/SOL (n=5,313)	1) HSI: abbreviated 17-item questionnaire that measures distress/worry associated with interpersonal, economic, and immigration conflict accompanying the process of adaptation and integration into a new nonnative culture within the past three months	1) Insomnia: Women’s Health Initiative Insomnia Rating Scale (WHIIRS) a 5-item questionnaire that asks respondents to rate how frequently they experience difficulty with sleep initiation and maintenance over the past four weeks 2) Daytime sleepiness: ESS, an 8-item questionnaire that asks respondents to rate their likelihood of falling asleep in eight different contexts 3) Sleep duration: calculated from self-reported average weekday bedtime and wake time	↓ Greater acculturation stress was associated with greater insomnia symptoms, after adjusting for sociodemographic characteristics, health behaviors and conditions, and other stressors (exp(b) = 1.06, 95% CI: 1.03-1.10) ↓ Greater acculturative stress was associated with greater daytime sleepiness, after adjusting for sociodemographic characteristics, health behaviors and conditions, and other stressors (exp(b) = 1.06, 95% CI: 1.02-1.10) → No association between acculturative stress and sleep duration
Suh et al. 2013 [54] Cross-sectional	Korean American adult women in Southeast U.S. (n=30)	1) Revised Social, Attitudinal, Familial, and Environmental Acculturative Stress Scale (R-SAFE): 25-item questionnaire to evaluate acculturative stress in multiple contexts	1) Sleep quality: PSQI, 19-item questionnaire designed to measure self-reported sleep quality during the previous month	↓ Higher acculturative stress was associated with worse daytime dysfunction, but was not associated with global sleep quality
Ehlers et al. 2010 [53] Cross-sectional	Mexican American young adults in San Diego County, CA (n=294)	1) Caetano Acculturation Stress Scale: 11-item questionnaire to evaluate acculturative stress	1) Sleep quality: PSQI, 19-item questionnaire designed to measure self-reported sleep quality during the previous month	↓ Acculturative stress was associated with poorer global sleep quality
3. Proxy Measures of Acculturation
García et al. 2020 [20] Cross-sectional	Nationally representative sample of U.S.-born non-Latino white adults vs. U.S.-born and non-U.S.-born Latino adults in NHIS 2004-2017 (n=303,204)	1) Citizenship: self-reported citizenship status 2) Length of residence in U.S.: self-reported years lived in the U.S. 3) Language: language of interview	1) Sleep duration: self-reported average hours of sleep in a 24-hour period	↑ Non-U.S.-born Puerto Ricans, Dominicans, Cubans, and Central/South Americans, and “Other” Latinos had greater odds of short sleep duration than their U.S.-born counterparts ↓ Non-U.S.-born Mexicans had lesser odds of short sleep duration than their U.S.-born counterparts
Gaston et al. 2020 [57] Cross-sectional	Nationally representative sample of U.S.-born non-Hispanic white adults vs. U.S.-born and non-U.S.-born Mexican, Puerto Rican, Cuban, Dominican, and Central/South American adults in NHIS 2004-2017 (n= 283,767)	1) Language: language of interview	1) Sleep duration: self-reported average hours of sleep in a 24-hour period 2) Sleep quality: self-reported number of nights with trouble falling asleep, trouble staying asleep, frequent sleep medication use, and waking up feeling rested in the week before the interview	↓ Overall, only Puerto Rican homeowners were more likely than NH-Whites to report <6 hours and 6-<7 hours of sleep duration; sensitivity analyses suggest that associations between housing tenure status and sleep vary by language acculturation and heritage group. Puerto Rican participants with high acculturation (English language of interview) had slightly worse sleep duration and quality than Puerto Rican participants with low acculturation (Spanish language of interview)
Murillo et al. 2019 [12] Cross-sectional	Nationally representative sample of Latino adults of Mexican/Mexican American, Puerto Rican, Dominican, Central or South American, and Cuban/Cuban American origin in NHIS 2013-2015 (n=13,537)	1) U.S.-born vs. non-U.S.-born: self-reported place of birth 2) Length of residence in U.S.: self-reported years lived in the U.S.	1) Sleep duration: self-reported average hours of sleep in a 24-hour period	↓ Compared to U.S.-born participants, non-U.S.-born participants living in the U.S. for any amount of time were less likely to have a short sleep duration in models that adjusted for age, sex, education, marital status, employment status, and Latino subgroup ↓ Non-U.S. born participants who lived in the U.S. for <10 years were more likely to have a normal sleep duration than those who lived in the U.S. for ≥10 years Those who lived in neighborhoods with medium and high social cohesion (vs. low) were significantly more likely to report normal sleep duration and these associations differed by Latino subgroup
Patel et al. 2015 [58] Cross-sectional	Hispanic/Latino adults in four major metropolitan areas (Bronx, NY; Chicago, IL; Miami, FL; and San Diego, CA) as part of HCHS/SOL (n=11,860)	1) U.S.-born vs. non-U.S.-born: self-reported place of birth 2) Length of residence in U.S.: self-reported years lived in the U.S.	1) Sleep duration: self-reported average hours of sleep, computed as the weighted average of weekday and weekend sleep (difference between habitual wake time and bedtime)	↓ Compared to U.S.-born Hispanic/Latinos, non-U.S.-born Hispanic/Latinos who lived in the U.S. for ≥10 years had decreased odds of both short sleep (aOR=0.84, 95% CI: 0.68, 1.03) and long sleep (aOR=0.78, 95% CI: 0.62, 0.99) in models that adjusted for demographic and socioeconomic variables ↓ Odds of both short sleep and long sleep were slightly higher in non-U.S.-born Hispanic/Latinos who have lived in the U.S. for 10 or more years, vs. <10 years
Jackson et al. 2014 [79] Cross-sectional	Nationally representative sample of U.S.-born and non-U.S.-born non-Hispanic Asian and non-Hispanic white adults in NHIS 2004-2011 (n=125,610)	1) U.S.-born vs. non-U.S.-born: self-reported place of birth	1) Sleep duration: self-reported average hours of sleep in a 24-hour period	↓ Most Asian participants were non-U.S.-born (74%), and U.S.-born participants had shorter sleep duration than non-U.S.-born participants; the Asian-White disparity was largest in certain sectors (e.g., finance/information, healthcare)
Whinnery et al. 2014 [55] Cross-sectional	Nationally representative sample of adults in NHANES 2007-2008 (n=4,850)	1) U.S.-born vs. non-U.S.-born: self-reported place of birth 2) Language: self-reported primary language spoken at home	1) Sleep duration: self-reported usual hours of sleep on weekdays or work nights	↓ Mexico-born participants reported less short sleep than U.S.-born participants (aOR=0.63, 95% CI: 0.41, 0.90) ↓ Spanish-only speakers reported less very short sleep
Manber et al. 2013 [62] Cross-sectional	Pregnant Hispanic/Latino adult women receiving perinatal services in 10 community obstetric/gynecologi c clinics serving the greater San Diego, California area (n=1,289)	1) Language: language of interview	1) Insomnia: ISI, a 7-item instrument which assesses the nature, severity, and impact of insomnia	↓ Completing the interview in English was a predictor of clinically significant insomnia (OR=2.61, 95% CI: 1.80, 3.79)
Young et al. 2013 [25] Cross-sectional	Hmong adults in Wisconsin (n=747)	1) Length of residence in U.S.: self-reported years lived in the U.S. 2) Diet: self-reported Hmong or Western diet 3) Religion: self-reported religious practices (Shamanism, Christianity, or other)	1) Sleep problems: self-reported occurrence and frequency of sleep apnea (snoring, breathing pauses), REM-related disorders (sleep paralysis at sleep onset, waking, and mid-sleep), hypnogogic hallucinations, nightmares, cataplexy, insomnia, and excessive daytime sleepiness (EDS) 2) Sleep apnea (sub-sample only): in-home portable polysomnography to measure apnea-hypopnea index (AHI) for a sub-sample of participants (n=37)	↓ Participants who lived in the U.S. for >10 years had higher odds of snoring than those who lived in the U.S. <10 years ↓ Participants who lived in the U.S. for >10 years had higher odds of nightmares than those who lived in the U.S. for <10 years ↑ Participants who practiced Shamanism had higher odds of hypnogogic hallucinations than those who practiced Christianity or other religions → No other associations between diet and religion and sleep problems
Heilemann et al. 2012 [60] Cross-sectional	Hispanic/Latino adult women in an urban Northern California community (n=312)	1) U.S.-born vs. non-U.S.-born: self-reported place of birth 2) Language: self-reported preferred language 3) Early U.S. socialization: immigration to the U.S. before 18 years of age	1) Sleep disturbance: General Sleep Disturbance (GSDS), a 21-item instrument for sleep disturbance in the past seven days	→ Sleep disturbance did not differ by country of birth ↓ Participants who preferred English reported more sleep disturbances than women who preferred Spanish
Hale et al. 2011 [28] Cross-sectional	Nationally representative sample of U.S.-born vs. non-U.S.-born Mexican adults in NHIS 1990 (n=1,436)	1) U.S.-born vs. non-U.S.-born: self-reported place of birth	1) Sleep duration: self-reported average hours of sleep in a 24-hour period	↓ U.S.-born Mexican Americans are more likely to be short sleepers than non-U.S.-born Mexican immigrants in models that adjusted for demographic, socioeconomic, and health behavior variables, including stress, smoking, and BMI (aOR=1.25)
Seicean et al. 2011 [18] Cross-sectional	Nationally representative sample of U.S.-born Mexican adults vs. non-U.S.-born Mexican adults in NHANES 2005-2006 (n=1,042)	1) U.S.-born vs. Mexico-born: self-reported place of birth 2) Language: self-reported language spoken at home	1) Short habitual sleep time (SHST): self-reported usual hours of sleep on weekdays or work nights 2) Insomnia: self-reported insomnia as defined by the NHLBI working definition 3) Sleep quality: self-re- ported perception of insufficient sleep during the past month or “trouble sleeping” ever reported to a physician or other health professional	↓ Mexico-born immigrant status was associated with lower odds of SHST (aOR=0.7, 95% CI: 0.6-0.9), insomnia (aOR=0.3, 95% CI: 0.2-0.5), and sleep-associated functional impairments (aOR=0.4, 95% CI: 0.2-0.8) ↓ Overall, there was a lower prevalence of poor sleep and poor sleep-related outcomes in Mexico-born immigrants vs. general U.S. population and to U.S.-born Mexican Americans ↓ Among Mexican American men, increased levels of English (vs. Spanish) spoken at home associated with increased risk of poor sleep
Seicean and Seicean 2010 [61] Cross-sectional	Nationally representative sample of Mexican-born vs. other Latino-born adults in NHANES 2005-2006, 2007-2008 (n=1,806)	1) Mexico-born vs. non-Mexico-born: self-reported place of birth 2) Proportion lifetime in immigration (PLI): calculated by dividing self-reported years lived in the U.S. by participant age 3) Language: self-reported language spoken at home	1) Insomnia: self-reported insomnia as defined by the NHLBI working definition	↓ Mexico-born ethnicity had a protective effect against severe insomnia (aOR=0.4, 95% CI: 0.2, 0.7) after adjusting for sociodemographic characteristics, health behaviors and conditions, and immigration-related characteristics ↓ Among Mexico-born immigrants, a greater PLI was associated with higher adjusted odds of severe insomnia → No association between English-use at home and severe insomnia
Chakraborty et al. 2003 [56] Cross-sectional	Mexican American adult women from Starr County, TX as part of the Unidos en Salud: Weight Loss for Mexican Americans study (n=390)	1) Migration History Score (MHS): 9-item questionnaire to measure migration history, including birthplace of participant, birthplace of participant’s parents and grandparents, and length of residence in the U.S.	1) Sleep duration: number of hours spent sleeping per night over the past week, measured with the 7-day Physical Activity Recall	→ Migration history score was not associated with sleep duration (logit α SE= −0.197 α .146)
4. Multiple acculturation measures (i.e., acculturation scale and proxy measure)
Ryu et al. 2021 [59] Cross-sectional	Nationally representative sample of non-Hispanic Asian/Native Hawaiian/Other Pacific Islander adults in the National Epidemiologic Survey on Alcohol and Related Conditions-III (NESARC-III) 2012-2013 (n=1,401)	1) Bidimensional Acculturation Scale (BAS): two sets (English and Asian language) of 12-item questionnaires measuring frequency of language use, electronic media consumption, and linguistic proficiency 2) U.S.-born vs. non-U.S.-born and length of residence in U.S.: additionally included proxy variables of acculturation, self-reported place of birth and years lived in the U.S.	1) Sleep duration: self-reported average number of hours of sleep on a typical day in the past month 2) Sleep difficulties: self-reported trouble falling asleep or staying asleep in the past twelve months	↑ Sleep duration longer than recommended among Bicultural and Asian orientation groups, vs. non-Asian orientation group, in models that adjusted for sociodemographic characteristics, comorbidities, and health behaviors; sensitivity analyses showed this is is driven by long sleep in Bicultural group ↑ Non-U.S.-born Asian participants living in U.S. for 6-20 years and for ≥21 years reported 0.17 and 0.28 hours per day shorter sleep duration, respectively, vs. U.S.-born Asian participants in models that adjusted for sociodemographic characteristics, comorbidities, health behaviors, acculturation → No association for non-U.S.-born Asian participants who lived in the U.S. for ≤5 years → After adjusting for sociodemographic characteristics, comorbidities, and health behaviors, there was no association between the BAS acculturation measure and sleep difficulties ↓ Non-U.S.-born Asian participants who lived in the U.S. for ≤5 years had lower odds for trouble falling asleep than U.S.-born individuals in models that adjusted for sociodemographic characteristics, comorbidities, health behaviors, and acculturation, and the protective association attenuated with longer years lived in the U.S.
Shen and Gellis 2021 [15] Cross-sectional	College students at a private university in northeastern U.S., including English as a Second Language (ESL) students (n=352)	1) SASH: adapted English language questions only from the 12-item questionnaire measuring language use, media preference, and ethnic and social relations in Hispanic populations 2) Language: self-reported native English language status	1) Insomnia: ISI, a 7-item instrument which assesses the nature, severity, and impact of insomnia	→ No significant association between language acculturation measured via SASH and insomnia severity ↑ ESL students reported higher levels of insomnia severity than English-only native students and were more likely to meet criteria for insomnia (OR = 2.88) after adjusting for race, gender, non-sleep depression, anxiety

^aStudies are ordered chronologically by publication date within each acculturation measurement subheading

^bThe direction of the arrow refers to evidence of positive or negative acculturation: ↑ indicates positive acculturation, or that U.S. acculturation is beneficial to the sleep outcome; ↓ indicates negative acculturation, or that U.S. acculturation is harmful to the sleep outcome; → indicates no association between U.S. acculturation and the sleep outcome.

Abbreviations: ARSMA-II=Acculturation Scale for Mexican-Americans-II; ESS=Epworth Sleepiness Scale; HCHS/SOL=Hispanic Community Health Study/ Study of Latinos; HSI=Hispanic Stress Inventory; ISS=Insomnia Severity Index; NHANES=National Health and Nutrition Examination Survey; NHIS=National Health Interview Survey; NHLBI=National Heart, Lung, and Blood Institute; PROMIS=Patient-Reported Outcomes Measurement System; PSQI=Pittsburgh Sleep Quality Index; SAS-K=Short Acculturation Scale for Koreans; SASH=Short Acculturation Scale for Hispanics; SWAN=Study of Women’s Health Across the Nation

Study quality rating

The NHLBI study quality ratings ranged from 5 to 11 and are available for each study in Table A.1. Overall, the average study quality rating was 6.8, qualitatively a “Fair” rating. The highest scores were given to the two longitudinal studies [38,39] which received a “Good” rating. Studies using proxy measures of acculturation, on average, scored lower than studies that used scales or questionnaires.

Measures of acculturation

The measurement methods for acculturation varied widely across studies and included acculturation scales, acculturative stress questionnaires, and proxy measures of acculturation. The acculturation questionnaire names and proxy variables that were utilized are summarized in Table A.2.

Sleep health dimensions and disorders measurements

Sleep outcomes evaluated in these studies included sleep duration/timing, sleep quality/continuity, daytime sleepiness, and sleep disorders (Table 1). Sleep duration was the most frequently evaluated sleep outcome. However, only one study measured objective sleep duration via actigraphy [40], and only one study measured sleep apnea via in-home portable polysomnography [25]. The overall associations of acculturation with each of the sleep health dimensions and disorders are summarized in Table 3.

Table 3.

Summary of evidence of positive or negative acculturation on various sleep health dimensions and disorders by measure of acculturation in a systematic review on acculturation and sleep health and sleep disorders in adult immigrant populations in the United States.

Acculturation Measurement	Sleep Duration/Timing	Sleep Quality/Continuity	Daytime Sleepiness	Sleep Disorders
Acculturation scales	MR [19,38,39,41–43,59]	MR [19,39,42–46,48,59,63,77]	MR [42,48,78]	MR [15,42,43,46–50]
Acculturative stress	MR [14,17,40,51,52]	↓ [17,40,52–54]	↓ [14]	↓ [14,40]
Proxy measures of acculturation	MR [12,18,20,28,55–59,79]	MR [18,57,59,60]	→ [25]	MR [15,18,25,61,62]

Note: The direction of the arrow refers to consistent evidence of positive or negative acculturation: ↑ indicates positive acculturation, or that U.S. acculturation is beneficial to the sleep outcome; ↓ indicates negative acculturation, or that U.S. acculturation is harmful to the sleep outcome; → indicates no association between U.S. acculturation and the sleep outcome; and “MR” indicates mixed results

Association between acculturation scales and sleep duration/timing

Overall, the results for the association between acculturation scales and sleep duration/timing were mixed. In a study of Hispanic/Latino women in Los Angeles, CA, Cantero et al. observed no significant differences in the prevalence of short sleep duration between their low (53.4%), medium (54.5%), and high (53.4%) acculturation groups, a three-level categorical variable constructed by trichotomizing the continuous acculturation scale developed by the study authors [41]. Similarly, in a study of Hispanic/Latino adult women in southeast Texas, Kachikis et al. found no association between acculturation measured using the Short Acculturation Scale for Hispanics (SASH) and sleep duration after adjustment for sociodemographic characteristics, depression, anxiety, and perceived stress [19]. Ghani et al. also found no association between Mexican acculturation measured with the Acculturation Scale for Mexican-Americans-II (ARSMA-II) and sleep duration among Mexican adults living along the U.S.-Mexico border; however, they did find that increasing levels of Anglo acculturation were associated with less sleep on weekends in models that adjusted for sociodemographic characteristics (β=−41.07, 95% CI: −73.6, −58.49) [42].

A study that found an association between acculturation scales and sleep duration/timing examined immigrant generation. Martinez-Miller et al. used the ARSMA-II and found that second-generation (GEN2) Hispanic/Latino participants with stable-high intergenerational U.S. acculturation had a higher prevalence of short sleep duration than participants with low intergenerational U.S. acculturation (PR=2.86, 95% CI: 1.02-7.99) [43].

Association between acculturation scales and sleep quality/continuity

Among the n=11 studies that evaluated the association of acculturation measured by scales on sleep quality/continuity, n=6 (55%) showed evidence of negative acculturation, or that cultural orientation towards the origin country was associated with better sleep quality. Among Mexican adults in Ghani et al.’s study, increasing levels of Anglo acculturation measured by the ARSMA-II were associated with lower weekend sleep efficiency (β=−4.26, 95% CI: −7.09, −1.43) and worse sleep quality (β=1.13, 95% CI: 0.42-1.84) in models that adjusted for sociodemographic characteristics [42]. Kachikis et al. used the SASH questionnaire in a diverse cohort and found that higher acculturation was associated with poorer sleep quality in fully adjusted models that included sociodemographic characteristics, depression, anxiety, and perceived stress (β=−0.06, SE=0.02) [19]. In the analyses conducted by Martinez-Miller et al. that included immigrant generation, they found that first-generation (GEN1) older Latinos with high U.S. acculturation, compared with high acculturation towards another origin/ancestral country, had less restless sleep (PR=0.67, 95% CI: 0.54-0.84) and a higher likelihood of being in the best sleep class than the worst (OR=1.62, 95% CI: 1.09-2.40) [43].

There was also evidence that acculturation was not associated with sleep quality. A study that examined Hispanic/Latino women in Newark, NJ with the SASH questionnaire, found no differences in the median sleep problem score between the low acculturation group (3.0, IQR: 0.0-6.0) and the high acculturation group (3.0, IQR: 0.0-5.0) [44]. Similarly, a study of older Korean immigrants in southern California that used a modified version of the SASH, the Short Acculturation Scale for Koreans (SAS-K), found that there were no significant differences in sleep quality by acculturation level [45].

There was some evidence that specific components of acculturation scales, specifically the language components, may be associated with sleep quality. A study using a modified version of the SASH that only included the language components of the questionnaire found that language acculturation or unmeasured factors associated with language acculturation mediated 40.4% (95% CI: 28.5%-69.8%) of the association between immigrant status and any sleep complaint [46]. Similarly, a study of 73 Bangladeshi immigrant parents living in New York City that used the Abbreviated Multidimensional Acculturation Scale (AMAS), a measure of English competence, found that an increase in parental English competence was associated with a decrease in reported sleep problems (β=−0.78, SE=0.33) [47].

Association between acculturation scales and sleep disorders

Most of the evidence supported that orientation towards U.S. culture was associated with more sleep disorders (63%). In a study of Hispanic/Latino adults with moderate to severe obstructive sleep apnea (OSA), the minimally symptomatic class was the least acculturated group [48] and in another study of Mexican adults, increasing levels of Anglo acculturation was associated with an increased risk for sleep apnea (β=5.57, 95% CI: 1.64-9.49) as well as insomnia (β=1.32, 95% CI: 0.44-2.20) in models that adjusted for sociodemographic characteristics [42]. There was also evidence that acculturation had a negative impact on restless leg syndrome (RLS). A study of Hispanic adults of Mexican descent found that those with high acculturation had significantly higher RLS prevalence than those with low acculturation (17.4% vs. 12.8%, respectively) [49].

Studies have also shown null findings between acculturation and sleep disorders. In a multi-ethnic study of midlife women, there was no association between acculturation and sleep symptoms among the total sample, though the sub-sample of Hispanic participants showed that Hispanic women who were more acculturated tended to report more sleep-related symptoms and a higher total severity [50]. Further, in a study of college students, Shen et al. found that there was no significant association between language acculturation measured via the SASH questionnaire and insomnia severity measured via the Insomnia Severity Index (ISI) [15].

Association between acculturative stress and sleep duration/timing

The two studies that evaluated the association of acculturative stress on sleep duration/timing among Hispanic individuals both demonstrated a fairly consistent null association between acculturative stress and sleep duration/timing measured both objectively and subjectively. Alcántara et al. demonstrated that among Hispanic participants, there was no association between acculturative stress and sleep duration calculated from self-reported average weekday bedtime and wake time [14]. Building upon these results, in their 2019 study, Alcantara et al. provided each participant with an Actiwatch Spectrum wrist actigraph to be worn on their nondominant wrist for one week and found that acculturative stress was not associated with any of the 7-day actigraphy measures, i.e., sleep duration, sleep efficiency, or sleep variability [40]. However, among Asian individuals, Park et al. found that in Korean women, higher homesickness and lower civic disengagement, subscales of the Acculturative Stress Index (ASI), were associated with shorter sleep duration, and in Korean men, higher isolation was associated with shorter sleep duration, in models that adjusted for sociodemographic characteristics, comorbidities, sleep environment, and acculturation [51]. Similarly, Lee et al. found that among Korean and Chinese Americans in the Washington D.C. metropolitan area, a one-unit increase in acculturative stress, measured by an adaptation of the HSI, was associated with 0.08 fewer hours of sleep in models that adjusted for sociodemographic characteristics and chronic conditions (β=−0.08, SE=0.04) [52].

Association between acculturative stress and sleep quality/continuity

Evidence supports that increasing levels of acculturative stress have a negative effect on subjectively measured sleep quality/continuity, but not objectively measured sleep efficiency. Two studies, one among Mexican American young adults [53] and the other among Korean American adult women [54], used the Pittsburgh Sleep Quality Index (PSQI) to measure sleep quality. Among the Mexican American young adults, those who reported acculturative stress had a higher global PSQI score, indicating worse sleep quality, than those who did not report acculturative stress [53]. Among the Korean American adult women, acculturative stress was not associated with global sleep quality, but was associated with worse daytime dysfunction. In a larger study of 400 Korean and Chinese Americans, greater acculturative stress was associated with a higher prevalence of sleep disturbance in the past seven days in models that adjusted for sociodemographic characteristics and chronic conditions (aPR=1.18, 95% CI: 1.06-1.31) [52]. Effect measure modification tests suggested that this association was only significant for women (aPR=1.30; 95% CI: 1.13-1.49) and those who identify as “very Asian” (aPR=1.21; 95% CI: 1.08-1.35). A study examining acculturative stress and sleep efficiency via actigraphy found no association [40].

Association between acculturative stress and daytime sleepiness

A study among Hispanic participants evaluated the effect of acculturative stress on daytime sleepiness using the Epworth Sleepiness Scale (ESS) [14]. Greater acculturative stress was associated with greater daytime sleepiness, after adjusting for sociodemographic characteristics, health behaviors and conditions, and other stressors (exp(b) = 1.06, 95% CI: 1.02-1.10). There were no additional studies examining acculturative stress and daytime sleepiness.

Association between acculturative stress and sleep disorders

Two studies used the HSI questionnaire to measure acculturative stress among Hispanic/Latino adults in four major metropolitan areas (Bronx, NY; Chicago, IL; Miami, FL; and San Diego, CA) as part of the HCHS/SOL cohort. Greater acculturative stress was associated with greater insomnia symptoms in both studies, after adjusting for sociodemographic characteristics, health behaviors and conditions, and other stressors [14,40].

Association between acculturation proxies and sleep duration/timing

Utilizing country of birth to approximate acculturation had mixed results on sleep duration/timing. However, most of the evidence (71% of the studies reviewed) suggested that non-U.S.-born Hispanic immigrants, especially Mexico-born immigrants, were less likely to have a short sleep duration compared to U.S.-born participants. For example, in an analysis of a nationally representative sample of U.S.-born and non-U.S.-born Mexican adults in the 1990 National Health Interview Survey (NHIS), Hale et al. found that U.S.-born Mexican Americans were more likely to be short sleepers than non-U.S.-born Mexican immigrants in models that adjusted for sociodemographic characteristics, stress, smoking, and BMI [28]. Similarly, two separate analyses of 2005-2006 and 2007-2008 National Health and Nutrition Examination Survey (NHANES) data found that U.S.-born Mexican Americans had shorter sleep than their Mexican-born counterparts [18,55]. However, there was conflicting evidence from a study of Mexican American women that showed that country of birth was not associated with sleep duration [56]. Further, other studies found that specific subgroups of Hispanic participants, such as non-U.S.-born Dominicans, Cubans, and Central/South Americans were in fact more likely to have short sleep duration compared to U.S.-born participants [20] and there is evidence that this disparity is particularly large for Puerto Ricans [57].

Some studies examined the length of time the participants spent living in the U.S. as a proxy for acculturation. In general, there appears to be a trend in these studies wherein longer time spent in the U.S. is disadvantageous to sleep health. For example, in Murillo et al.’s study on a nationally representative sample of Latino adults, non-U.S.-born participants who lived in the U.S. for less than 10 years were more likely to have a normal sleep duration than those who lived in the U.S. for 10 or more years [12]. Similarly, in Patel et al.’s study of the HCHS/SOL cohort, the odds of both short sleep and long sleep were slightly greater in non-U.S.-born Hispanic/Latinos who have lived in the U.S. for 10 or more years, compared to less than 10 years [58]. This loss of sleep health advantage with longer durations in the U.S. is also seen in studies of Asian populations. In Ryu et al.’s study of a nationally representative sample of non-Hispanic Asian/Native Hawaiian/Other Pacific Islander adults, non-U.S.-born Asian participants living in the U.S. for ≥21 years reported 16.8 minutes shorter sleep duration per day compared to U.S.-born Asian participants in models that adjusted for sociodemographic characteristics, comorbidities, health behaviors, and acculturation [59]. Non-U.S.-born Asian participants living in the U.S. for 6-20 years reported 10.2 minutes shorter sleep duration per day.

Association between acculturation proxies and sleep quality/continuity

English language as a proxy for U.S. acculturation was consistently associated with poorer sleep quality among all studies that examined Hispanic/Latino immigrants (n=3). Preferring to speak in English or using the English language at home was associated with more sleep disturbances among Hispanic/Latino adult women in an urban Northern California community [60]. However, in this same sample, sleep disturbance did not differ by acculturation when estimated by country of birth. Puerto Rican participants who completed their interview in English had slightly worse sleep quality than Puerto Rican participants who completed their interview in Spanish [57]. Among Mexican American men, increased levels of English spoken at home (compared to Spanish) were associated with an increased risk of poor sleep [18].

Similar to the results found for sleep duration, there was evidence that suggested that longer residence in the U.S. was associated with poorer sleep quality. Non-U.S.-born Asian participants who lived in the U.S. for ≤5 years had lower odds for trouble falling asleep than U.S.-born individuals in models that adjusted for sociodemographic characteristics, comorbidities, health behaviors, and acculturation, and the protective association attenuated with longer years lived in the U.S. [59].

Association between acculturation proxies and daytime sleepiness

A study among Hmong immigrants in Wisconsin evaluated the effect of length of residence in U.S., diet, and religion on daytime sleepiness and found no significant associations [25]. There were no additional studies examining proxies for acculturation and daytime sleepiness.

Association between acculturation proxies and sleep disorders

All studies that evaluated the effect of acculturation proxies on sleep disorders evaluated insomnia (n=5). Non-U.S.-born Hispanic participants were less likely to have severe insomnia compared to U.S.-born participants [61], and Mexico-born ethnicity had a protective effect against severe insomnia (aOR=0.4, 95% CI: 0.2, 0.7) after adjusting for sociodemographic characteristics, health behaviors and conditions, and immigration-related characteristics [61]. Again, longer residence in the U.S. appeared to be detrimental to health, as a study of Mexico-born immigrants showed that a greater proportion lifetime in immigration was associated with higher adjusted odds of severe insomnia [61]. However, when using language as a proxy for acculturation, there was evidence from a study of U.S. college students that English as a Second Language (ESL) students reported higher levels of insomnia severity than the English-only native students and were more likely to meet criteria for insomnia after adjusting for race, gender, non-sleep depression, and anxiety [15]. Lastly, in a nationally representative sample of U.S. adults there was no association between speaking English at home and severe insomnia [61].

Acculturation and sleep in sub-populations

Three of the included studies examined sub-populations that warrant separate discussion. In the studies conducted by D’anna-Hernandez et al. [39] and Manber et al. [62], the participants included Hispanic women during pregnancy. D’anna-Hernandez et al. utilized the SASH questionnaire to examine sleep duration, sleep onset, sleep disruptions, and feeling refreshed upon waking longitudinally throughout pregnancy. Manber et al. used language of interview as a proxy for acculturation to examine insomnia severity in pregnant women receiving perinatal services in 10 community obstetric/gynecologic clinics. In both studies, the authors found evidence of negative acculturation. In longitudinal analyses, D’anna-Hernandez et al. found that women who were more acculturated reported more times up during the night and lower feelings of being refreshed upon awakening across pregnancy [39]. In Manber et al.’s cross-sectional analysis, they found that completing the interview in English was a predictor of clinically significant insomnia (OR=2.61, 95% CI: 1.80, 3.79) [60].

Gonzalez et al. examined sleep quality among a group of Chinese breast cancer survivors who lived throughout the U.S. [63]. Using the Stephenson Multigroup Acculturation Scale (SMAS) and the PSQI, they found that the mean acculturation score for breast cancer survivors with a total PSQI score <5 was not meaningfully different than the mean acculturation score for participants with a PSQI score ≥5 [63].

Discussion

As evidenced in this systematic review, there is high prevalence of adverse sleep health dimensions and disorders among immigrant populations in the U.S., and acculturation likely plays an important role in shaping this disparity. However, studies examining the effect of U.S. acculturation on sleep health dimensions and disorders utilized a wide range of measurements of acculturation and subjective measures of sleep, causing primarily mixed results. Overall, there was no consistent association between acculturation scales and sleep duration/timing, sleep quality/continuity, daytime sleepiness, or sleep disorders in the included studies. The most consistent evidence for acculturation and sleep health was the harmful effect of acculturative stress on sleep. All studies found that higher levels of acculturative stress were associated with worse sleep quality/continuity, daytime sleepiness, and sleep disorders. The direction of these associations was also consistent across different racial/ethnic groups. Finally, the evidence for the effect of acculturation proxies on sleep duration/timing, sleep quality/continuity, and sleep disorders was also mixed, though acculturation measured via language proxy variables was associated with worse sleep quality/continuity among Hispanic immigrants specifically.

Based on the synthesis of the published articles, we developed a conceptual model illustrating the possible links between acculturation and sleep and possible effect modifiers that can guide future sleep research among immigrant populations (Figure 2). This conceptual model illustrates how acculturation may lead to health behaviors, psychosocial factors, and/or barriers to healthcare access, that ultimately shape sleep health. Factors such as socioeconomic status, immigrant generation, occupation, and neighborhood ethnic composition may modify the association between acculturation and sleep health (Figure 2).

Figure 2.

Conceptual model linking acculturation to sleep health and sleep disorders with potential mediators and modifiers based on the qualitative synthesis of the articles featured in this systematic review.

Based on our review of the literature, we offer a number of suggestions to advance the literature on acculturation and sleep health.. First, studies that examine sleep duration should differentiate between weekday and weekend sleep. Ghani et al. differentiated between weekday and weekend sleep duration and found that increasing levels of Anglo acculturation were associated with less sleep on weekends, but not weekdays [42]. The authors hypothesized that those with more Anglo orientation may be employed in jobs with more typical weekday work hours and have a consistent weekday sleep schedule, while their weekend sleep may be disrupted by social events and activities. Next, because culture is shaped over generations, future acculturation and sleep research should collect information on immigrant generation. Martinez-Miller et al. differentiated between immigrant generation and found that second-generation (GEN2) Hispanic/Latino participants with stable-high intergenerational U.S. acculturation had a higher prevalence of short sleep duration than participants with low intergenerational U.S. acculturation [43]. Next, Lee et al. determined that the association between acculturative stress and sleep disturbance was only significant among participants who described their ethnic identity as “very Asian” [52]. Strong ethnic identity could modify the association between acculturative stress and sleep health, as those with higher ethnic identity tend to experience acculturative stress with greater threat and vulnerability [52]. Future studies should explore ethnic identity as an effect measure modifier of acculturation and sleep. Lastly, we discovered that self-reported measures of acculturation, such as those assessed via acculturative stress scales, were more strongly related to self-reported sleep outcomes, as opposed to objectively-measured sleep outcomes. These findings are consistent with other sleep-related research studies (e.g., self-reported chronic burden is more strongly correlated with self-reported sleep duration) [64] and with studies from other fields (e.g., subjective assessments of satisfaction are more strongly correlated with subjective well-being [65]). However, there were only two studies with objectively-measured sleep outcomes included in our review; future studies should confirm whether self-reported measures of acculturation correlate more strongly with self-reported perceptions of sleep by conducting studies with an array of both subjective and objective sleep measurements.

We additionally discovered evidence for both the Healthy Immigrant Effect and negative acculturation within this review. For example, for sleep duration, most evidence suggested that non-U.S.-born Hispanic immigrants, particularly Mexico-born immigrants, were less likely to have a short sleep duration compared to their U.S.-born counterparts. Further, studies that examined the length of time participants spent living in the U.S. found that this initial health advantage diminishes the longer time is spent living in the U.S. [12,58,59]. However, little is known about what causes this deterioration in health and using duration of residence in the U.S. as a proxy for acculturation may not represent the true causal processes. Future research is needed to understand what experiences or exposures are causing the loss in health advantage. For example, immigrant populations could be experiencing prolonged exposure to social and economic disadvantage, similar to the weathering hypothesis, which causes deterioration of sleep health. Alternatively, if time spent in the U.S. does serve as an appropriate proxy for adopting U.S. culture and behaviors, immigrant populations could be engaging in negative health behaviors that lead to declines in health.

This systematic review also uncovered the wide range of measurements of acculturation in the sleep health literature. Thomson et al.’s systematic review examining how public health literature among U.S. Hispanic populations defined and measured the concept of acculturation found considerable variation and little theoretical orientation in the way acculturation was measured, lending uncertainty around what precisely acculturation was measuring [66]. Within acculturation scales, for example, there is a wide range in strength of measurement. Unidimensional questionnaires, such as the ARSMA [67] and the SASH [68], present acculturation as a linear process from losses on the “unacculturated” end to gains on the “acculturated” end [66]. Bidimensional questionnaires, such as the Bidimensional Acculturation Scale (BAS) [69], include two separate scales to measure change in the culture of origin and the new culture individually [66]. However, acculturation is likely a process of reciprocal interactions between the individual and the environment, which multidimensional questionnaires, such as the ARSMA-II [70], try to measure by examining multiple dimensions of the acculturative process (such as attitudes, values, and ethnic interaction) individually [23,66]. Therefore, the association between acculturation and sleep health dimensions and disorders can vary considerably by scale. Moreover, the associations can vary even when the same scale is used. For example, Kachikis et al. [19] used the SASH questionnaire on a diverse cohort and found that higher acculturation was associated with poorer sleep quality, but a study of Hispanic/Latino women and a study of Korean immigrants in southern California using the same scale found that there were no significant differences in sleep quality by acculturation level [44,45].

Despite the development of validated acculturation scales, many studies rely on proxy measures of acculturation because they are quick and convenient to collect, with fairly satisfactory correlation to other questionnaires. However, the acculturation scales and proxy variables do not provide consistent evidence both within their own categories and with each other. For example, while most studies that utilized country of birth as a proxy for acculturation suggested that non-U.S.-born Hispanic immigrants, specifically Mexico-born immigrants, were less likely to have a short sleep duration compared to U.S.-born participants, other studies that used acculturation scales concluded that there was no association between acculturation and sleep duration. Further, many studies that did not collect information on acculturative stress hypothesized that the effect of sleep outcomes they observed for proxy measurements of acculturation, such as country of birth, is evidence that stressful experiences due to cultural changes and racial/ethnic discrimination explain the observed association. If acculturative stress or discrimination are the theorized causes of these poor sleep health, validated measures for acculturative stress and discrimination, such as the Hispanic Stress Inventory [71] or the Everyday Discrimination Scale [72], should be used over proxy measurements for acculturation. If researchers are hypothesizing that something truly cultural is contributing to sleep health and disorders for immigrants, validated measures for acculturation, as well as social factors that influence acculturation (e.g., social support, collective efficacy, familism) should be incorporated into the study design.

Therefore, future sleep health studies focused on understanding the effect of acculturation should further elucidate the causal mechanisms between acculturation and sleep health. By clarifying the theoretical framework, researchers can better understand how acculturation can best be measured in their study. For example, there was some evidence that specific components of acculturation scales, specifically the language components, could be associated with sleep quality. A multiethnic study of women found that language acculturation likely mediated the association between immigrant status and any sleep complaint [46] and a study of Bangladeshi immigrant parents found that an increase in parental English competence was associated with a decrease in reported sleep problems [47]. More evidence is needed to understand if stressors due to language proficiency mediate the association between acculturation and sleep health.

This systematic review also uncovered some weaknesses in the acculturation and sleep health literature. Among our 38 studies, only two studies included an objective measurement of sleep. Objective measurements of sleep like actigraphy provide the ability to quantify sleep continuity and sleep timing over time, thus future sleep research on immigrant populations should aim to include objective measures of sleep into their study designs. Further, when objective measures are not possible, studies should include validated sleep questionnaires instead of relying on singular questions. Previous literature has established that although self-reported sleep is limited by various reporting biases, sleep measured via validated questionnaires is a patient-reported outcome that is both important to patients and a predictor of important health end points [64,73]. We also noted that only two of our studies were longitudinal, and the remaining were cross-sectional studies. Though many of the cross-sectional studies included large, representative samples of the U.S. population, additional longitudinal evidence to establish temporality and causation between acculturation and sleep health is needed. Further, although multiple studies did examine the heterogeneity within Hispanic/Latino and Asian populations, there is still limited evidence for racial/ethnic groups and subgroups. Specifically, mostly Chinese and Korean ethnicities were examined in the studies that included Asian populations, no studies included in this review examined African immigrants, and both studies with Caribbean immigrants only included people from the Dominican Republic. Lastly, none of the included studies controlled for individual behavioral variables like personality, which is associated with acculturation [74] and sleep health [75]. van der Zee et al. explains “personality dispositions might predict whether the psychological experiences derived from intercultural contact and change are seen as challenging and stressful, or whether they are seen as positive and enriching experiences” [74].

Our systematic review has a few limitations. First, we excluded sleep studies that included a proxy measure of acculturation, such as country of birth, but did not explicitly state that their proxy measure was intended to approximate acculturation, which could potentially bias our conclusions for that category. However, the primarily mixed results that we observed for studies with proxy measures was as expected, given proxy measures may not approximate the experience of acculturation well. Further, it was not in the scope of this review to include all studies that included a proxy measure of acculturation, and although n=14 studies were excluded due to this criterion, we have summarized all the sleep health studies that explicitly intended to investigate acculturation. Additionally, although we conducted our study quality appraisal using the NHLBI criteria and with multiple, independent reviewers, assigning each study a qualitative rating from the quantitative scores was inherently a subjective process and the scores should be interpreted as such. Next, this review only included studies with adult participants, thus limiting the applicability of the results to younger immigrant populations across various stages of development. Given the importance of cultural and racial/ethnic identity development during childhood and adolescence, future research should explore the association between acculturation and sleep health among immigrant children and adolescents. Lastly, a quantitative assessment of the effect size of the relationship between acculturation and sleep health was not included in this review, thus future reviews should conduct meta-analyses in order to quantify the overall association.

Conclusions

Immigrant health scholars have argued for a theory-driven model of acculturation in public health research. However, as evidenced in this systematic review, studies examining the effect of U.S. acculturation on sleep health dimensions and disorders have utilized a wide range of acculturation measures, leading to mixed results. By simplifying acculturation and by categorizing immigrant populations into boxes such as “ethnic” or “assimilated” without truly considering what our measure of acculturation is measuring, we can inadvertently assign blame to individuals for structural causes of health disparities [23]. Rather than over-relying on cultural explanations for health outcomes that may obscure the impact of structural causes, many argue for a shift from individual culture-based frameworks to perspectives that address how multiple dimensions of inequality, such as immigrants’ experiences with day-to-day discrimination, intersect to shape health outcomes [76]. The most consistent evidence for the association of acculturation and sleep health was the harmful effect of acculturative stress, which can capture these dimensions of inequality, on sleep quality/continuity, daytime sleepiness, and sleep disorders. Future sleep studies among immigrant populations should use a multifactorial, social epidemiological approach to sleep health [31] to further understand the theoretical mechanisms and multilevel mediators and effect modifiers of acculturation and sleep health.