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. Author manuscript; available in PMC: 2026 Jun 6.
Published in final edited form as: Psychoneuroendocrinology. 2026 Jan 13;186:107755. doi: 10.1016/j.psyneuen.2026.107755

Sex-specific associations between loneliness and hair cortisol among older African American adults

Katherine Knauft a, Jacqueline Rodriguez-Stanley b, Kristin M Davis c, Lance M Rappaport d, Francesca Luca e, Nataria T Joseph f, Christopher G Engeland g,h, Samuele Zilioli c,i,*
PMCID: PMC13238461  NIHMSID: NIHMS2170373  PMID: 41539174

Abstract

Loneliness has been linked to increased risk of cardiovascular disease, which disproportionately affects African American adults. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, as measured by long-term accumulation of cortisol in hair, may be one pathway through which loneliness increases cardiovascular disease risk. However, the relationship between loneliness and hair cortisol levels among African American adults has not yet been explored. Further, both loneliness and cortisol activity differ across age and sex. To better understand the association between loneliness and HPA axis activity among middle-aged and older African American adults, the present study examined the degree to which age and sex interacted with loneliness to predict hair cortisol concentrations. Data were obtained from 340 African American adults (Mage = 66.06, SD = 5.46, range = 55–75; 87.1 % female), who provided hair samples and reported their loneliness level as a part of The Heart of Detroit Study. Results showed that sex significantly moderated the association between loneliness and hair cortisol. Loneliness was positively associated with hair cortisol concentrations in male, but not female, participants. These findings suggest that sex-specific associations may exist between loneliness and hair cortisol.

Keywords: Social connectedness, Loneliness, HPA axis, Hair cortisol, Aging, African American

1. Introduction

Establishing meaningful social connection is a human need associated with health and happiness (Baumeister and Leary, 1995). Loneliness is defined as the perception of insufficient social companionship, and, though related, it is distinct from objective lack of social contacts (i. e., social isolation; Coyle and Dugan, 2012). Data from the American Association of Retired Persons and the Health and Retirement Study suggest that between 25 % and 29 % of older adults in the US report experiencing loneliness at least occasionally (Ong et al., 2016). Loneliness has adverse effects on health, including increased risk of hypertension, cardiovascular disease (CVD; Christiansen et al., 2021), and premature mortality (Holt-Lunstad et al., 2015). Loneliness may increase morbidity and mortality through negative effects on health behaviors and by increasing emotional and physiological reactivity to stressful experiences (Hawkley and Cacioppo, 2007; Holt-Lunstad et al., 2015). A key pathway is the dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, which is hypothesized to be implicated in the link between loneliness and CVD (Hawkley and Cacioppo, 2007; Quadt et al., 2020). However, the full extent to which loneliness is associated with HPA axis activity has yet to be fully delineated.

Most of the existing research on the links between loneliness and activity of the HPA axis has focused on salivary cortisol, which reflects circulating cortisol levels (Stalder and Kirschbaum, 2012). With regard to salivary cortisol, loneliness has been linked to lower cortisol awakening responses, flatter diurnal cortisol slopes, and higher cortisol levels at bedtime (Johar et al., 2021; Montoliu et al., 2019; Schutter et al.,2017). However, other studies found no association between loneliness and diurnal cortisol patterns (Zilioli and Jiang, 2021). Less research has investigated the relationship between loneliness and hair cortisol, which reflects the amount of cortisol that accumulates in the hair follicles over multiple weeks to months and is considered a biomarker of chronic stress (Iob and Steptoe, 2019). Loneliness can be a chronic experience among older adults (Laustsen et al., 2024). Because hair cortisol is a marker of the chronic activation of the HPA axis, it is an ideal candidate when studying the link between loneliness and CVD. Accordingly, hair cortisol concentrations have been associated with systolic blood pressure, cardiometabolic health (e.g., triglycerides, cholesterol, glycated haemoglobin), and incidence of CVD events (Iob and Steptoe, 2019). For example, in one study, researchers analyzed hair samples of patients who recently suffered a myocardial infarction and found significantly higher cortisol concentrations in the month preceding the event compared to healthy controls (Faresjö et al., 2020). To fully establish chronic activation of the HPA axis as a pathway linking loneliness to cardiovascular health, more work is needed to determine whether loneliness is associated with hair cortisol levels among older adults. Further examination of the link between loneliness and hair cortisol is needed among African Americans, who experience elevated risk of CVD (Mohebi et al., 2022).

Age may influence the link between loneliness and HPA axis activity. As adults age, diurnal cortisol output tends to increase (Gaffey et al., 2016). For example, older age was associated with greater daily cortisol output across 10 days in a sample of healthy, older adults (Nater et al., 2013). Hair cortisol concentrations were also linearly associated with increasing age in a large sample of middle-aged and older adults (Feller et al., 2014). In their systematic review, Gaffey and colleagues put forth a model of age-related increases in cortisol, highlighting the potential roles of psychosocial factors (Gaffey et al., 2016). The authors argued that effective emotion regulation and supportive social relationships may act as key buffers to age-related changes in cortisol output, while social strain may be a catalyst to them. Compared to younger adults, older adults tend to selectively prioritize emotionally rewarding relationships, favoring quality over quantity (Carstensen et al., 1999). Furthermore, middle and older adulthood have been found to contain lifetime peaks and lows for average loneliness, suggesting that experiences of loneliness can meaningfully fluctuate between the ages of 55 and 75 (Luhmann and Hawkley, 2016). Simultaneously, the associations between negative aspects of social interactions and negative physical health consequences strengthen with age (Hakulinen et al., 2016; Rook and Charles, 2017). While these models focus on social networks, interactions, and support rather than directly addressing loneliness, it is reasonable to hypothesize that loneliness may also become more tightly associated with physiological and health-related outcomes as individuals age. Accordingly, the present study examined if the link between loneliness and hair cortisol is moderated by age.

Sex may also play a role in the association between loneliness and HPA axis function. Some work among older adults suggests that men report greater loneliness and social isolation than women (Compernolle et al., 2021; Cudjoe et al., 2020; R. J. Taylor et al., 2019), although the opposite has also been found (Pinquart and Sorensen, 2001). Beyond these potential differences in loneliness levels, the relationship between loneliness and health outcomes may also vary by sex, with some evidence suggesting that men might be more vulnerable than women to the negative effects of loneliness on health. For example, among men but not women, loneliness has been found to be associated with depression (Zebhauser et al., 2014) and premature mortality (Holwerda et al., 2012), including CVD-related mortality (Olsen et al., 1991). Additionally, sex differences in the effect of loneliness on daily cortisol secretion have been observed among older adults (Díaz-Mardomingo et al., 2023). Among male participants, higher levels of loneliness were associated with higher awakening cortisol levels, higher cortisol output, and a steeper diurnal cortisol slope. In female participants, no associations between loneliness and cortisol emerged. These findings suggest that sex might moderate the relationship between loneliness and hair cortisol levels.

The present study examines the connection between loneliness and HPA axis activity in the form of hair cortisol among older African American adults. In light of the potential moderating roles of age and sex, we examined the degree to which age and sex interacted with loneliness to predict hair cortisol concentrations. Study hypotheses and analyses were preregistered on the Open Science Framework (https://osf.io/67yuc).1 First, we hypothesized that higher levels of loneliness would be associated with higher levels of hair cortisol. Second, we expected that higher loneliness would interact with age and sex to predict higher levels of hair cortisol among older African American adults. Specifically, we anticipated that links between loneliness and hair cortisol would be stronger for male and older participants, compared to female and younger participants.

2. Methods

2.1. Participants

Data for the study were drawn from the first wave of The Heart of Detroit Study (THDS), which examines biobehavioral pathways that connect psychosocial experiences to CVD in a sample of middle-aged and older African American adults (N = 522) living in Metro Detroit (Davis et al., 2023). The main exclusion criteria for THDS included a history of CVD, HIV/AIDS infection, neurodegenerative disease, psychiatric disorders, or cognitive impairment. As the outcome of the present study was hair cortisol, participants who did not provide hair samples (n = 182) were excluded from the present analysis. Reasons for missing hair samples included the participant declining to provide the sample, use of protective styles (e.g., braids and dreadlocks), or a lack of hair (e.g., hair that was not long enough to provide a sample). Comparisons of those with and without hair samples suggested that the subset who provided hair samples was more likely to be female,younger, and have higher SES than those who did not provide hair samples but did not differ on any other variables of interest (See Table 1). The analytic sample for this study was 340 participants (Mage = 66.06, SD = 5.46, range = 55–75; 87.1 % female). Data collection occurred between September 2021 and December 2023. Participants were recruited through the Wayne State University Institute of Gerontology Participant Pool, snowball sampling, social media advertisements, and advertisements placed in the community.

Table 1.

Comparison of participants with and without hair samples.

Hair subsample M(SD) No hair subsample M(SD) p-value
Age 66.06 (5.46) 65.05 (5.52) .045
SES 0.06 (0.88) −0.12 (0.91) .025
Loneliness 5.20 (2.26) 4.90 (1.80) .121
BMI 33.14 (8.23) 32.44 (8.07) .374
Depressive symptoms
 0.60 (0.47)
 0.62 (0.53) .683
n (%) n (%)
Sex < .001 a
Male 44 (12.9) 105 (57.7)
 Female 296 (87.1) 77 (42.3)
Chronic conditions .055a
0 102 (30.0) 74 (40.7)
 1 100 (29.4) 45 (24.7)
 2 +
 138 (40.6) 63 (34.6)
Marital status .233a
Not married/cohabitating 250 (73.5) 125 (68.7)
 Married/cohabitating 90 (26.5) 57 (31.3)
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Note. SES = Socioeconomic status (standardized); BMI = Body mass index;

a

= Welch’s t-test

2.2. Procedures

Details of the THDS study protocol have been previously published (Davis et al., 2023). Briefly, participants completed two home-based visits, separated by a seven-day period of ecological momentary assessment (EMA). During the first home visit, participants provided written informed consent and completed questionnaires assessing demographic information and physical and psychological health, including loneliness. Following the seven-day EMA period, participants completed a second home visit. At this time, research staff collected anthropometric, physical health, and biological data, including hair samples. Participants received monetary compensation for their participation. The Wayne State University Institutional Review Board approved all study procedures, and study procedures were conducted in accordance with the Declaration of Helsinki.

2.3. Materials

2.3.1. Loneliness

Loneliness was assessed via the Short Loneliness Scale (SLS; Hughes et al., 2004). The SLS is a three-item questionnaire measuring how often participants generally feel dissatisfied with their current level of social connections. Participants responded to each question on a four-point Likert scale ranging from 1 (Never) to 4 (Very often). There were no missing values in the SLS. Therefore, the items were summed to create a total loneliness score, such that higher scores reflected more feelings of loneliness. The SLS has shown convergent validity with the revised UCLA Loneliness Scale (Hughes et al., 2004). The scale had adequate reliability in the present study (α =.76; Bland and Altman, 1997).

2.3.2. Hair cortisol

For participants who consented to provide the hair sample, a section of hair 2 cm below the cranial bone that was at least 3 mm in diameter was separated from the rest of the hair. The section of hair was cut at the scalp and sealed in aluminum foil. Cortisol concentrations from the hair (pg/mg) were quantified with a commercially available luminescence immunoassay (IBL International, Hamburg, Germany) at the Dresden LabService (Dresden, Germany). Gao et al. (2013) detail the extraction and assay procedures for the LC–MS/MS-based method used for the present study. In brief, steroid hormones (e.g., cortisol) were extracted from hair via methanol incubation, a column-switching on-line solid phase extraction was applied, and analytes were detected via mass spectrometer. The lower limits of quantification for the assay were equal to or below 0.1 pg/mg for cortisol. Assays for the present study were conducted in two batches. Intra-assay coefficients of variation (CV) were 9.9 % and 10.4 %, and inter-assay CVs were 12.1 % and 15.0 %.

2.3.3. Covariates

Demographic covariates included self-reported sex assigned at birth (0 = male, 1 = female), age in years, marital status (0 = unmarried, 1 = married or cohabitating), and socioeconomic status (SES). SES was measured as a composite of participants’ educational attainment and yearly household income. The composite score was obtained by standardizing and then averaging the two variables. Health-related covariates included current prescription medication use (0 = no prescription medications, 1 = prescription medications), current chronic health conditions, and body mass index (BMI). The number of chronic conditions was assessed using a variable summarizing the number of conditions endorsed in a list of 16 chronic conditions (e.g., cancer, diabetes). Participants endorsing no conditions were coded as 0, participants endorsing one condition were coded as 1, and participants endorsing two or more conditions were coded as 2. BMI was measured as weight in kilograms divided by height in meters squared.2 Finally, depressive symptoms were measured using the 10-item short form of the Center for Epidemiological Studies Depression scale (CES-D-10, Andresen et al., 1994). Participants answered each item using a 4-point scale, ranging from 0 (rarely or none of the time) to 3 (most or all of the time). Following previous studies, one item about loneliness was dropped from the scale to avoid direct overlap with the primary loneliness variable (Steptoe et al., 2013). A composite score for depressive symptoms was calculated by reverse coding items 5 and 8 and then averaging responses across the 9 items, with higher scores reflecting more severe depressive symptoms. Reliability of the CES-D-10 was adequate, but in the questionable range (Bland and Altman, 1997), in the present sample (α =.68).

Three variables related to hair care (chemical treatment, heat styling, and recent dyeing) were also considered as covariates. Consistent with previous investigations (Moody et al., 2022), all three variables were unrelated to hair cortisol concentrations (ps > .116); therefore, they were dropped from analyses.

2.4. Analytic strategy

Unless otherwise specified, analyses were performed in R (R Core Team, 2021). After excluding participants who did not provide hair samples, 0.33 % of data on the remaining variables were missing. Categorical missing data were handled using mode imputation, and continuous missing data were handled using the expectation maximization (EM) algorithm in SPSS Version 29.0 (Enders, 2001).

Though some previous studies found hair cortisol concentrations in African American samples tend to be higher than hair cortisol concentrations in samples of other races (Fiedler et al., 2024; Lehrer et al., 2020; Louis-Jacques et al., 2024), our data included raw hair cortisol concentrations that were extremely high (Mdn = 43.12, SD = 20, 590.90, range = 0.5 – 320,852.0 pg/mg). Hair cortisol values > 1000 pg/mg are thought to reflect use of topical corticosteroids, rather than endogenous cortisol production (Kostolanská et al., 2022). However, this cut-off value came from a sample from the Czech Republic, so it is unclear if the exact cut-off value can be generalized to other populations including African American adults. Previous work examining hair cortisol concentrations in samples that include African Americans have identified outliers as those who exceed 3 standard deviations (Lehrer et al., 2020) or the 90th percentile (Vargas et al., 2025). In the present sample, a few extreme values inflated the standard deviation; therefore, we used the 90th percentile to identify outliers. The 90th percentile value in the present study was 783.42 pg/mg. Thirty-four participants exceeded this threshold, leaving a final N of 306 participants in the primary analyses. All participants who were dropped due to extreme values (>90th percentile) were female. It is possible that high hair cortisol levels were due to hair treatments such as peroxide use, which may explain why all outliers were female (Hoffman et al., 2014). These participants were dropped from primary analyses, but results from the full sample are presented in Supplementary Materials. Following the removal of outliers, the distribution of hair cortisol concentrations remained positively skewed (Mdn = 36.59 pg/mg, SD = 159.04, range = 0.5 – 782.08 pg/mg). To correct for skewness among hair cortisol concentrations, values were log-transformed in all models.In line with statistical guidelines, a constant of 1 was added to each value prior to transformation (Van Bogart et al., 2022).

Ordinary least squares (OLS) regression analyses were performed to test the main effect of loneliness on hair cortisol concentration and the interactions between loneliness and age and loneliness and sex on hair cortisol concentrations. Loneliness and age were grand-mean centered to improve interpretability. First, unadjusted regression models were constructed, with hair cortisol concentrations regressed on age, sex, and loneliness. Then, partially adjusted analyses were run in which we controlled for demographic and health-related covariates. Finally, given overlap between loneliness and depressive symptoms (Cacioppo et al., 2010), fully adjusted analyses were run controlling for demographic covariates, health-related covariates, and depressive symptoms. Multivariate outliers with high influence as indicated by Cook’s distance were dropped from the relevant analyses to ensure that the results were not unduly influenced by these observations.

Associations between social isolation and weekly social interaction and hair cortisol concentration were also explored, but no predictors of interest emerged as significant in those sets of analyses (See Supplements 2 and 3).

3. Results

3.1. Descriptive statistics & bivariate correlations

Descriptive statistics and bivariate correlations for the sample can be found in Table 2. No significant bivariate associations emerged between hair cortisol concentrations and any predictors or covariates. Elevated loneliness was significantly associated with more chronic conditions and lower SES (See Table 2). Unmarried individuals [M (SD) = 5.56 (2.35)] reported significantly higher loneliness than married/cohabitating individuals [M (SD) = 4.18(1.61); t(230.96) = 6.15, p < .001].3 No significant sex differences in loneliness emerged [t(58.66) = −1.86, p = .068]3.

Table 2.

Descriptive Statistics and Correlations.

Variable M SD 1 2 3 4 5 6 7 8 9
1. Age 66.06 5.46 -
2. Chronic conditions 1.11 0.83 .08 [−.03,.19] -
3. Prescription medications 87.4a – .11* .32** -
[.01,.22] [.22,.41]
4. SES −0.01 0.89 .19*** −.06 .01 -
[.08,.29] [−.17,.04] [−.09,.12]
5. Female 87.1b – .01 .11* .04 .19*** -
[−.09,.12] [.01, 22] [−.06,.15] [.09,.29]
6. Married or cohabitating 26.5c – .06 −.02 −.04 .32** −.03 -
[−.04,.17] [−.13,.09] [−.14,.07] [.22,.41] [−.13,.08]
7. BMI 33.03 8.05 −.05 .15** .09 .02 .25** −.07 -
[−.15,.06] [.04,.25] [−.02,.19] [−.09,.12] [.15,.35] [−.18,.03]
8. Loneliness 5.20 2.26 −.01 .11* .06 −.21** .10 −.27*** −.04 -
[−.11,.10] [.00,.21] [−.05,.16] [−.31, −.11] [−.01,.20] [−.37, −.17] [−.14,.07]
9. Depressive symptoms 0.60 0.47 −.13* .10 .02 −.28** −.01 −.16** .01 .35** -
[−.23, −.02] [−.01,.20] [−.08,.13] [−.38, −.18] [−.12,.09] [−.26, −.05] [−.09,.12] [.26,.44]
10. Hair cortisol concentrationd 101.60 159.04 .05 −.03 −.04 −.05 .07 .03 .08 −.01 .08
[−.07,.16] [−.14,.08] [−.15,.07] [−.16,.06] [−.05, 18] [−.08,.14] [−.03,.19] [−.12,.10] [−.04,.19]
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Note. M = mean, SD = standard deviation; Brackets = 95 % confidence interval; SES = Socioeconomic status (standardized); BMI = Body mass index; Sex: Male = 0; Female = 1; Chronic conditions: 0 = no conditions, 1 = one condition, 2 = two or more conditions;

a

= % taking prescription medication;

b

= % female;

c

= % married/cohabitating;

d

= hair cortisol concentration log-transformed for correlations, but raw mean and standard deviation presented;

*

indicates p < .05,

**

indicates p < .01,

***

indicates p < .001.

3.2. Regressions

3.2.1. Main effects analysis

In unadjusted analyses, no main effects of loneliness (b = −0.01, p = .738), age (b = 0.01, p = .422), or sex (b = 0.26, p = .235) on hair cortisol concentration emerged (See Table 3). Similarly, no main effects emerged in partially adjusted analyses (Loneliness: b = −0.01, p = .805; Age: b = 0.02, p = .225; or Sex: b = 0.29, p = .216) or in fully adjusted analyses accounting for covariates that included depressive symptoms (Loneliness: b = −0.02, p = .525; Age: b = 0.02, p = .186; or Sex: b = 0.30, p = .207).

Table 3.

Analyses Predicting Hair Cortisol Concentration.

Main Effects Moderation by Sex Moderation by Age
Predictor b 95 % CI b 95 % CI b 95 % CI
Unadjusted Models
(Intercept) 3.51 ** [3.10, 3.91] 2.57 ** [0.68, 4.46] 3.51 ** [3.11, 3.91]
Loneliness −0.01 [−0.08, 0.05] 0.37 * [0.01, 0.72] −0.01 [−0.08, 0.05]
Sex 0.26 [−0.17, 0.70] −0.16 [−0.79, 0.46] 0.26 [−0.18, 0.69]
Age 0.01 [−0.02, 0.04] 0.02 [−0.01, 0.05] 0.01 [−0.02, 0.04]
Loneliness X Sex - - −0.41* [−0.77, −0.05] - -
Loneliness X Age - - - - −0.00 [−0.01, 0.01]
Partially Adjusted Models
(Intercept) 3.21 ** [2.43, 4.00] 3.71 ** [2.79, 4.63] 3.22 ** [2.43, 4.01]
Loneliness −0.01 [−0.08, 0.06] 0.37 * [0.01, 0.72] −0.01 [−0.08, 0.06]
Sex 0.29 [−0.17, 0.76] −0.11 [−0.75, 0.54] 0.29 [−0.17, 0.76]
Age 0.02 [−0.01, 0.05] 0.03 [−0.00, 0.06] 0.02 [−0.01, 0.05]
SES −0.16 [−0.35, 0.04] −0.18 [−0.36, 0.00] −0.16 [−0.35, 0.04]
Chronic conditions −0.08 [−0.28, 0.11] −0.10 [−0.28, 0.09] −0.08 [−0.28, 0.11]
Prescription medications −0.16 [−0.65, 0.33] −0.10 [−0.58, 0.39] −0.16 [−0.65, 0.33]
Marital status 0.18 [−0.19, 0.55] 0.09 [−0.27, 0.45] 0.18 [−0.19, 0.55]
BMI 0.01 [−0.01, 0.03] 0.01 [−0.01, 0.03] 0.01 [−0.01, 0.03]
Loneliness X Sex - - −0.42* [−0.78, −0.05] - -
Loneliness X Age - - - - −0.00 [−0.01, 0.01]
Fully Adjusted Models
(Intercept) 3.07 ** [2.26, 3.88] 3.55 ** [2.60, 4.51] 3.08 ** [2.26, 3.89]
Loneliness −0.02 [−0.10, 0.05] 0.33 [−0.04, 0.69] −0.02 [−0.10, 0.05]
Sex 0.30 [−0.17, 0.77] −0.06 [−0.71, 0.58] 0.30 [−0.17, 0.77]
Age 0.02 [−0.01, 0.05] 0.03 * [0.00, 0.06] 0.02 [−0.01, 0.05]
SES −0.13 [−0.32, 0.06] −0.16 [−0.35, 0.03] −0.13 [−0.33, 0.06]
Chronic conditions −0.09 [−0.28, 0.11] −0.10 [−0.29, 0.09] −0.09 [−0.29, 0.11]
Prescription medications −0.14 [−0.63, 0.34] −0.08 [−0.57, 0.40] −0.14 [−0.63, 0.35]
Marital status 0.18 [−0.19, 0.55] 0.09 [−0.27, 0.45] 0.18 [−0.19, 0.55]
BMI 0.01 [−0.01, 0.03] 0.01 [−0.01, 0.03] 0.01 [−0.01, 0.03]
Depressive symptoms 0.24 [−0.11, 0.60] 0.20 [−0.14, 0.55] 0.24 [−0.11, 0.60]
Loneliness X Sex - - −0.39 * [−0.75, −0.02] - -
Loneliness X Age - - - - −0.00 [−0.01, 0.01]
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Note. b = unstandardized regression weight; Loneliness and age = grand mean centered; SES = Socioeconomic status (standardized); BMI = Body mass index; Sex: Male = 0; Female = 1;

*

indicates p < .05.

**

indicates p < .01.

3.2.2. Moderation analyses

Age did not emerge as a significant moderator of the association between loneliness and hair cortisol concentration in unadjusted analyses (b = −0.00, p = .817), analyses controlled for demographic and health variables (b = −0.00, p = .889), or in fully adjusted analyses (b = −0.00, p = .859; See Table 3). In analyses testing the loneliness x sex interaction, sex emerged as a significant moderator of the association between loneliness and hair cortisol concentration in unadjusted (b = −0.41, p = .027), partially adjusted (b = −0.42, p = .025), and fully adjusted analyses (b = −0.39, p = .038; See Fig. 1). Examination of simple slopes suggested that higher loneliness was linked to significantly greater hair cortisol concentrations among male participants (unadjusted b =.37, p = .044; partially adjusted b =.37, p = .044), but there was no association between loneliness and hair cortisol concentrations among female participants in any analyses (ps > .114). In analyses controlling for depressive symptoms, the direction of the results remained the same, but the simple slope for male participants dropped below significance (fully adjusted b =.33, p = .079).

Fig. 1.

Fig. 1.

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Fully Adjusted Model of the Effect of Loneliness on Log-Transformed Hair Cortisol Moderated by Sex Assigned at Birth.

4. Discussion

The present study examined the independent and interactive effects of loneliness, sex, and age on hair cortisol in a sample of older African American adults. No main effects of loneliness, sex, or age on hair cortisol emerged in the primary analyses. Furthermore, loneliness and age did not interact to predict hair cortisol. A significant interaction between loneliness and sex emerged in both primary analyses and supplementary analyses that included extreme outliers (See Supplement 1). These effects were robust to the inclusion of demographic and health covariates. While loneliness was unrelated to hair cortisol among female participants, greater loneliness in male participants was associated with elevated hair cortisol levels. These results suggest that loneliness may be uniquely linked to chronic activation of the HPA axis among male older African American adults.

While studies of older adults have found associations between loneliness and salivary cortisol dynamics (Johar et al., 2021; Montoliu et al., 2019; Schutter et al., 2017)—which reflect daily circulating cortisol (Stalder and Kirschbaum, 2012)—relatively few studies have investigated associations between loneliness and hair cortisol, which is linked to more chronic HPA axis activity over the course of weeks to months. Each centimeter of hair reflects cortisol accumulation across approximately one month (Iob and Steptoe, 2019). Drawing on work employing salivary cortisol, there is some evidence among middle aged and older adults that social isolation, rather than loneliness, is more robustly related to cortisol (Zilioli and Jiang, 2021). Additionally, of the three studies that observed associations between loneliness and diurnal cortisol dynamics among older adults (Johar et al., 2021; Montoliu et al., 2019; Schutter et al., 2017), only one study (Schutter et al., 2017) observed an association between loneliness and overall cortisol output. It is possible that the associations between loneliness and alterations in cortisol secretion occur primarily through changes in diurnal rhythm, rather than overall cortisol output.

The lack of a significant main effect of loneliness on hair cortisol in the present study is concordant with some previous work examining loneliness and hair cortisol (Taylor et al., 2022). Using data from the English Longitudinal Study of Aging, Taylor and colleagues did not find a significant main effect of loneliness on hair cortisol in a sample of 2050 adults over the age of 50. However, a significant interaction did occur, such that loneliness and hair cortisol were negatively associated for individuals with low levels of early life adversity but positively associated for those with high levels of early life adversity. Though the present study did not specifically examine early life stress, these findings suggest that the association between elevated loneliness and higher hair cortisol concentrations may not be direct, but instead nuanced, such that the association only emerges among specific populations (e.g., men or individuals who have experienced early life adversity).

The present findings suggest that high loneliness is associated with elevated hair cortisol concentrations among male, but not female, older African American adults. To our knowledge, the present study is the first to examine sex-specific associations between loneliness and hair cortisol in this cohort. These results align with other findings that loneliness may have a greater physiological impact on men. In a study of older married adults aged 65–90, Johar et al. (2021) found that loneliness was associated with a flatter diurnal cortisol slope among men, but not women. Furthermore, a study of adults between the ages of 60 and 90 years found that men experiencing more loneliness had a steeper cortisol slope, elevated cortisol levels at awakening, and higher overall cortisol output throughout the day compared to those experiencing less loneliness (Díaz-Mardomingo et al., 2023). No such associations between loneliness and cortisol were found among women (Díaz-Mardomingo et al., 2023). Beyond the HPA axis, there is evidence that men may be more vulnerable to the consequences of loneliness. For example,incidence of premature mortality is significantly higher among lonely men compared to lonely women (Holwerda et al., 2012; Olsen et al., 1991). As such, the present finding extends our understanding of the sex-specific links between loneliness and HPA axis function. Older African American men may be more vulnerable to the physiological sequalae of loneliness, including chronic HPA axis activity, compared to women. Future work is needed to provide insight regarding the mechanisms underlying sex differences in the physical health consequences of loneliness.

While the interactive effect of loneliness and sex remained significant across primary models, it is important to note that the simple slope of the effect of loneliness on hair cortisol for male participants dropped below significance when depressive symptoms were included in the analyses. This finding raises questions about the overlap between loneliness and depressive symptoms, particularly among males. Depressive symptoms are frequently controlled for in examinations of the health-related sequalae of loneliness (see Steptoe et al., 2013), as there is substantial conceptual and experiential overlap between loneliness and depressive symptoms. Some examinations suggest that feelings of loneliness longitudinally predict, but are not longitudinally predicted by, changes in depressive symptoms (Cacioppo et al., 2010). For this reason, depressive symptoms have sometimes been conceptualized as a mediator between loneliness and health-related physiological processes (see Vingeliene et al., 2019). However, some research has found the opposite, with depressive symptoms predicting future loneliness, and no effect of loneliness on future depression in a sample of older adults (McHugh Power et al., 2020). Still other work suggests a bidirectional association between loneliness and depressive symptoms (Lee et al., 2021). Together, this previous work and the present study suggest that depressive symptoms may be part of the pathway linking loneliness to elevated hair cortisol, but more work is needed to test the temporal dynamics between these variables.

This study has notable strengths, including the large sample size and its focus on older African American adults. Despite these strengths, the study has some limitations. First, our sample had more female than male older adults. It is not uncommon for female participants to outnumber male participants among studies of the general population (Glass et al., 2015); older women outnumber older men in the general population and among African Americans (Administration on Aging, 2021; Tucker et al., 1993). Furthermore, older male participants are more frequently unable to provide an adequate hair sample, often due to balding or hair that is too short (Wright et al., 2015). Examination of differences between participants who provided hair samples and those who did not demonstrated that those who provided hair samples were more likely to be female, younger, and higher SES than those who did not provide hair samples. Next, the age range for the present sample was narrow (55–75), which may have reduced the likelihood of observing an age by loneliness interaction. These demographic differences underscore the need to replicate the present findings in a sample with more men, a wider age range of older adults, and of lower SES. Lastly, the alpha for the CES-D-10 was relatively low in the present sample. Previous work has noted that the factor structure of the CES-D among older African American adults differs somewhat from the expected factor structure (Long Foley et al., 2002) and found questionable construct validity of the CES-D among African American and Black Caribbean men (Torres, 2012). Thus, the low internal consistency in the present study may reflect a need for further validation of the CES-D-10 among older African American adults.

In addition, the cross-sectional nature of the present design precludes any conclusions about causality. Future examinations of longitudinal effects of loneliness on hair cortisol concentrations are needed to better understand the effects of loneliness on HPA axis function across time. Finally, loneliness was examined using a single trait-level questionnaire. Thus, we are unable to speak to intrapersonal changes in loneliness across time or to the potential roles of loneliness from specific sources (e. g., social, familial, romantic). A more fine-grained, longitudinal examination of state loneliness may provide additional insight into the experiences of loneliness most connected to hair cortisol concentration among older African American adults.

5. Conclusions

The present study is the first to examine the links between loneliness and chronic HPA axis activity, as measured by hair cortisol, among older African American adults. We found that older African American male adults with higher loneliness exhibited higher hair cortisol levels relative to those with lower loneliness. Conversely, older African American female adults exhibited no association between hair cortisol levels and loneliness. These findings indicate that loneliness may relate to higher chronic HPA activation in African American men. It is possible that interventions related to reducing loneliness may be one potential avenue for addressing physical and mental health risks linked to chronic activity of the HPA axis, such as cardiovascular disease, which African American are at particularly high risk for developing (Churchwell et al., 2020). Future research is needed to better understand these associations across longer time periods and to examine the potential health consequences of high hair cortisol among lonely older African American male adults.

Supplementary Material

supp_1

Funding

This study was supported by grants from the National Institutes of Health (1R01HL153377, P30AG015281) and the Michigan Center for Urban African American Aging Research (MCUAAAR).

Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.psyneuen.2026.107755.

Footnotes

CRediT authorship contribution statement

Knauft Katherine M: Writing – review & editing, Writing – original draft, Visualization, Formal analysis, Conceptualization. Jacqueline Rodriguez-Stanley: Writing – review & editing, Writing – original draft. Samuele Zilioli: Writing – review & editing, Supervision, Resources, Project administration, Methodology, Funding acquisition, Data curation, Conceptualization. Nataria T. Joseph: Writing – review & editing. Christopher G. Engeland: Writing – review & editing. Francesca Luca: Writing – review & editing. Kristin M. Davis: Writing – review & editing, Writing – original draft. Lance M. Rappaport: Writing – review & editing.

Declaration of Competing Interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article

1

No significant effects of hypothesized predictors on cortisone or DHEA levels emerged in any analyses and therefore are not reported here.

2

BMI was not included as a covariate in the original preregistration and was added in response to one reviewer’s feedback to further strengthen the analyses. Importantly, exclusion of BMI from the models yields an identical pattern of results.

3

Welch’s t-test

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