Race and Financial Strain are Independent Correlates of Sleep in Midlife Women: The SWAN Sleep Study

MOUNTING EVIDENCE SUGGESTS THAT SLEEP DIFFERS SIGNIFICANTLY ACROSS RACIAL AND ETHNIC GROUPS IN WAYS THAT MAY BE IMPORTANT TO health and functioning.1–5 Most consistent among these effects is a marked decrease in laboratory-assessed slow wave sleep and a concomitant increase in stages 1 and 2 of NREM sleep in African Americans compared to Caucasians.3–7 Other dimensions of sleep shown to differ between African Americans and Caucasians include sleep duration, continuity and subjective sleep quality, although these relationships are not as strong and consistent as those observed for sleep architecture.8 Far fewer studies have compared sleep across other racial and ethnic groups. Hale and Do9 evaluated data from 32,749 respondents to the 1990 health promotion supplement of the National Health Interview Survey (NHIS) and found that, compared to Caucasians, the prevalence of short sleepers (< 6 hours/night) was higher among all racial and ethnic minorities surveyed including African Americans, Hispanics and non-Hispanic “others.” As measured by one night of in-home polysomnography (PSG) collected in the population-based Sleep Heart Health Study (SHHS), Redline and colleagues reported that American Indians and African Americans had lighter sleep than Caucasians, Hispanics, or Asian Americans.10 Despite growing evidence that sleep differs by race and/or ethnic minority status, few studies have evaluated possible causes or correlates of these differences. It has been suggested that socioeconomic status (SES), which is closely tied to race and ethnic minority status in many countries, including the United States, may play an important role in the relationship between minority racial/ethnic status and disturbed sleep.5,6,11 Indeed, a number of studies have reported significant associations among subjective sleep complaints and various indices of SES including lower education, occupational status and income, although these studies did not evaluate the influence of race on the SES-sleep relationship.12–17 Three recent studies reported that both race/ethnicity and traditional measures of SES, income, and education, were significant correlates of behavioral or PSG-assessed indices of sleep.2,6,18 For instance, Mezick and colleagues evaluated the independent effects of race and SES on sleep in a cohort of midlife men and women who were self-identified as either non-Hispanic Caucasian or African American. Lower SES, as measured by a composite score of income and education, was associated with greater PSG-assessed wakefulness after sleep onset, after adjusting for other confounding variables, including race. Sleep quality, duration, and architecture were unrelated to SES in the Mezick et al., study. These studies provide some support for the hypothesis that certain dimensions of sleep may be related to traditional markers of SES, independent of race. The extent to which other dimensions of SES affect, or are affected by, sleep have received less empirical attention. We have hypothesized that financial strain, which is a key chronic stressor associated with lower SES, may be a sensitive marker of the SES-sleep relationship.11 We reported that financial strain, operationalized as difficulties with paying for basics like food and housing, was a significant correlate of increased subjective sleep quality complaints in a sample of 462 midlife women, one-third of whom were African American.11 In multivariate models, financial strain attenuated the relationship between income and sleep quality, which is consistent with the hypothesis that stress pathways are important to the SES-sleep relationship. Stress pathways by which financial strain might interfere with sleep include increased worries and negative affect, as well as endocrine and autonomic dysregulation.19–24 More recently, we demonstrated that chronic and ongoing financial strain was associated with significant decreases in PSG-assessed sleep efficiency in a large sample of community-dwelling elders, after adjusting for a host of variables known to impact sleep in late life.25 Although these studies suggest that financial strain may be an important correlate of sleep, the extent to which financial strain plays a role in the SES-sleep or race-sleep relationship has not been evaluated. The present study evaluated relationships among race and markers of SES in relation to sleep in a multiracial sample of midlife women enrolled in the SWAN Sleep Study, which was designed to characterize sleep during the menopausal transition. Sleep during the menopausal transition provides an opportune model for evaluating the influence of race and SES on sleep because subjective sleep complaints and some sleep disorders are much more frequent in perimenopausal and menopausal women.26–30 Moreover, sleep disturbances that arise during the menopausal transition may be a marker for the development of later chronic health conditions and declines in general health and functioning occurring in the postmenopausal years. SWAN Sleep Study participants included African American, Caucasian, and Chinese women. Measures of sleep were subjective sleep quality, as measured by the validated Pittsburgh Sleep Quality Index (PSQI),31 and indices of sleep duration, continuity, and architecture including NREM electroencephalographic (EEG) power, as measured by multinight in-home PSG. We hypothesized that African American race would be associated with worse sleep, compared to Caucasian and Chinese participants. We further hypothesized that markers of SES, as measured by educational attainment and financial strain, would affect the race-sleep relationship. Specifically, we hypothesized that lower educational attainment and financial strain would attenuate observed relationships among race and sleep after adjusting for other factors that might confound relationships among race, SES, and sleep in midlife women.