Acculturation and asthma in Asian American adults

To the Editor:

Limited evidence suggests that the prevalence of asthma is lower in non-Hispanic Asian American (heretofore referred to as Asian American) adults than in non-Hispanic white or Hispanic American adults. However, this finding may be due to ethnic differences in diagnostic patterns, as Asian American individuals have more frequent visits to the emergency department and urgent care visits for asthma than non-Hispanic white individuals^{1, 2}.

Acculturation is a significant predictor of asthma among Hispanic populations in the United States (U.S.), including Mexican Americans³ and Puerto Ricans⁴. Based on this observation, we hypothesized that acculturation would be associated with asthma and worse lung function in Asian American adults. To test this hypothesis, we examined the relation between acculturation, asthma, and lung function among Asian American adults who participated in the National Health and Nutrition Examination Survey (NHANES).

NHANES is a cross-sectional nationwide survey designed to assess the health and nutrition of the civilian non-institutionalized U.S. population, using a stratified multistage probability design to select a representative sample of such population. Ethnic minorities (including non-Hispanic Black, Hispanic, and (since 2011) Asian American subjects) and low-income persons (at or below 130% of the federal poverty level) are oversampled to increase statistical power for data analysis in these groups. We analyzed data from adults ages 18 to 79 years who participated in the NHANES study cycles from 2011–2012 to 2017–2018. Of 22,307 participating adults, 2,486 were eligible for this analysis, as they self-reported their ethnicity as non-Hispanic and their race as Asian (only), had complete information on asthma status and relevant covariates, and had no self-reported diagnosis of chronic obstructive pulmonary disease or COPD (which could be misclassified as asthma). A flow chart for selection of the participants is available from the authors upon request. NHANES is approved by the Institutional Review Board of the National Center for Health Statistics of the Centers for Disease Control. Informed consent is obtained from all study participants.

Current asthma was defined by a positive answer to both of the following questions: “Has a doctor or other health professional ever told you that you have asthma?” and “Do you still have asthma?”. Control subjects were participants without current asthma (i.e., those who reported never having had asthma diagnosed by a healthcare professional and those who reported a previous diagnosis of asthma by a healthcare professional but denied still having asthma). Eligible participants performed spirometry following American Thoracic Society and European Respiratory Society recommendations. Percent predicted (%pred) values for forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), and FEV₁/FVC were calculated using Global Lung Initiative (GLI) 2012 equations⁵.

A composite acculturation index⁶ was created using three variables: nativity status (birth in the 50 U.S. states or in Washington, DC vs. others), length of time living in the U.S. (<5 years, 5-<20 years, or ≥ 20 years), and language spoken at home (no English, English and at least one other language, or only English). Three categories of acculturation (low, medium, and high) were then created and used for the analysis of acculturation level (see Table E1 in the Online Repository).

Primary sampling units and strata for the complex NHANES survey design were considered for data analysis. Sampling weights, stratification, and clusters provided in the NHANES dataset were incorporated into the analysis to obtain proper estimates and their standard errors. Two-sided chi-square tests and t-tests were used for bivariate analyses. Logistic or linear regression was used for the multivariable analysis of acculturation and current asthma or lung function. All multivariable models were adjusted for private health insurance coverage, body mass index (BMI, kg/m2), family history of asthma, serum cotinine (a major metabolite of nicotine that is used as a marker of both active smoking and exposure to second-hand smoke), and smoking status (categorized as never, former, or current); models for asthma were additionally adjusted for age and gender.

Compared to control subjects (n=2,375), subjects with current asthma (n=111) were older and more likely to report a family history of asthma, to have a higher BMI, to have been born in the 50 U.S. states or in Washington DC, to have lived in the U.S. ≥ 20 years, to speak only English at home, and to have a higher level of acculturation (Table E2). Subjects with current asthma also had lower FEV₁ and FEV₁/FVC than control subjects.

The results of the multivariable analysis of acculturation and current asthma are shown in Table 1. In this analysis, birth in the 50 U.S. states or in Washington, D.C., living in the U.S. for ≥20 years, and speaking only English at home were significantly associated with 2.26 to 3.15 times increased odds of current asthma (models 1–3 in the first column of Table 1). Moreover, subjects with high acculturation had 4.28 times higher odds of current asthma than those with low acculturation (model 4 in the first column of Table 1). We obtained similar results in a secondary analysis of acculturation and having ever had asthma, in which control subjects were those who never had asthma (available from the authors upon request).

Table 1–

Multivariable analysis of acculturation and current asthma in non-Hispanic Asian American adults

Variables	All participants (n=2486)	Never smokers (n=1908)
	Odds ratio (95% confidence interval)
Model 1: Nativity *
Birth outside the 50 U.S. states or Washington, D.C.	1.0	1.0
Birth in the 50 U.S. states of Washington, D.C.	3.15 (1.95 to 5.08)†	4.53 (2.57 to 8.01)†
Model 2: Length of residency in the U.S.
< 20 years	1.0	1.0
≥ 20 years	2.68 (1.69 to 4.23)†	3.08 (1.73 to 5.50)†
Model 3: Language(s) spoken at home
No English	1.0	1.0
English and at least one other language	1.27 (0.82, 1.97)	1.09 (0.61, 1.94)
Only English	2.26 (1.55 to 3.30)†	2.05 (1.31 to 3.21)†
Model 4: Acculturation level
Low	1.0	1.0
Medium	1.77 (0.95, 3.28)	1.83 (0.85, 3.92)
High	4.28 (2.37 to 7.71)†	4.85 (2.20 to 10.71)†

All models adjusted for age, gender, private insurance coverage, family history of asthma, body mass index, serum cotinine level, and (in all participants) smoking status.

^*P<0.05;

^†P<0.01.

To reduce potential misclassification of COPD as asthma and to account for potential residual effects of smoking, we also repeated the analysis after excluding former and current smokers, obtaining similar results (models 1–4 in the second column of Table 1).

Table 2 shows the results of the multivariable analysis of acculturation and percent predicted lung function measures. In this analysis, subjects with high acculturation had 3.65% to 4.23% lower %pred FEV₁ and %pred FVC than those with low acculturation (P=0.06 in both instances).

Table 2 –

Multivariable analysis of acculturation and percent predicted lung function measures (n=566)

	Acculturation
	Low	Medium	High
Lung function measures	β (95% CI)
%predicted FEV1	Reference	2.77 (−1.12 to 6.67)	−3.65 (−7.52 to 0.22)*
%predicted FVC	Reference	1.60 (−2.84 to 6.05)	−4.23 (−8.66 to 0.21)*
%predicted FEV1/FVC	Reference	1.06 (−0.48 to 2.60)	0.48 (−0.89 to 1.84)

All models adjusted for asthma status, private health insurance coverage, family history of asthma, serum cotinine level, and smoking status.

^*P=0.06

Consistent with findings in other ethnic groups, high acculturation and each acculturation measure (nativity status, time living in the U.S., and language spoken at home) were significantly associated with current asthma in Asian American participants^{6, 7}. This association was present in Asian American adults with and without family history of asthma, further suggesting that acculturation is a key risk factor for asthma in this population. Although high acculturation was associated with lower FEV₁ and FEV₁/FVC, this association was not significant at P <0.05.

Our study was limited by a cross-sectional design, small sample size, and lack of data for specific subgroups of Asian Americans (some of which have been reported to differ with regard to asthma prevalence^{8, 9}) and confounders such as atopy, history of childhood asthma, and exposure to air pollutants. Nonetheless, our results support an association between high acculturation and asthma in Asian American adults, a fast-growing group that is often been under-represented in studies of asthma in the U.S.

Our novel findings should stimulate future longitudinal studies of potential causes of the acculturation-asthma link in Asian American adults, including but not limited to obesity, immigration-related stress, and changes in dietary patterns and lifestyle. Because the Asian American population is heterogenous, such studies should aim to compare adequate samples of well-defined subgroups such as Chinese, Koreans, Japanese, Filipinos, and Indians.

Clinical implications:

High acculturation was associated with asthma in Asian American adults, even after accounting for smoking. Factors associated with acculturation (e.g., diet and obesity) should be addressed when caring for Asian American patients with asthma.