Ethnic differences in electroencephalographic sleep patterns in adolescents

Abstract

The purpose of the study was to evaluate ethnic differences in polysomnography measures in adolescents. Ninety-six volunteers from four ethnic groups (13 African-American, 18 Asian-American, 19 Mexican-American, and 46 Non-Hispanic White) were recruited. The subjects were in good physical and psychological health, and were asymptomatic with respect to sleep/wake complaints or sleep disorders. Polysomnography measures were collected on three consecutive nights. African-Americans manifested lower sleep efficiency, spent proportionately more time in stage 2 sleep, and had less stage 4 sleep compared to the other ethnic groups. In contrast to this, Mexican-Americans had more rapid eye movement (REM) sleep than their counterparts. The observed sleep patterns in the different ethnic groups persisted after controlling for specific demographic, clinical and psychosocial variables that are known to influence sleep measures. Gender had a differential effect on sleep patterns in the various ethnic groups. For instance, differences in non-REM sleep were more evident in African-American males, whereas increased REM sleep was most notable in Mexican-American females. At present, the clinical implications of the observed cross-ethnic differences in sleep physiology among adolescents are not clear. In previous studies, reduced sleep efficiency and stage 4 sleep, as well as increased REM sleep, were associated with psychopathology. It is not known whether the traditionally described sleep profiles, based largely on Non-Hispanic White populations, will generalize to other racial or ethnic groups. In addition to a systematic investigation of this issue, future research should attempt to identify the underlying causes for cross-ethnic variations in sleep physiology.

Introduction

There is evidence of ethnic/racial disparities in the prevalence and burden of disease for a broad spectrum of physical and mental disorders. For example, the prevalence of diabetes in African-Americans and Mexican-Americans is almost double that of the rates observed in Non-Hispanic Whites, whereas Asian-Americans are more than 5 times likely to suffer from tuberculosis than the rest of the US population (Centers for Disease Control and Prevention, 2006, Centers for Disease Control and Prevention, 2007). On the other hand, the prevalence of osteoporosis is highest among Non-Hispanic Whites (Department of Health and Human Services, 2007). Ethnic/racial differences also have been reported with regard to prevalence rates, symptom profiles and treatment response for different psychiatric disorders (Alegría et al., 2007, Breslau et al., 2006, Goodman et al., 2008, Lin, 2001). The underlying causes for such ethnic/racial disparities are not well-understood, but there is a consensus that they are likely to be multi-dimensional including socioeconomic and cultural factors, access to health care services as well as genetic/biological differences (Abe-Kim et al., 2007, Collins, 2004, Lin, 2001, Takeuchi et al., 2007). Among the latter, variations in sleep patterns might play a contributory role.

Sleep is a fundamental neurobehavioral state linked to critical domains of health and functioning, including attention, learning and memory, mood regulation, as well as metabolic, endocrine, immune and cardiovascular functions (Banks and Dinges, 2007, Barnard and Nolan, 2008, Smolensky et al., 2007). Prospective epidemiological studies demonstrated that sleep disruption is associated with medical conditions that are highly prevalent in our society, including cardiovascular disease, diabetes, and obesity (Knutson and Van Cauter, 2008, Miller and Cappuccio, 2007). Sleep dysregulation also is associated with a wide array of psychiatric disorders, including anxiety, mood and addictive disorders (Breslau et al., 1996, Buysse et al., 2008, Germain and Kupfer, 2008). Although there is evidence of a strong genetic influence on circadian sleep rhythm and sleep architecture, they are also highly sensitive to socio-cultural factors (Barnard and Nolan, 2008, Kimura and Winkelmann, 2007). Therefore, it is likely that ethnic/racial factors significantly impact the sleep system.

Given the growing interest on the relationship between ethnicity and health, and based on the evidence of sleep effects on health, it is surprising that relatively few studies exist on ethnic differences in sleep. Albeit limited, data from diverse lines of investigation, including self-report, behavioral and physiological assessments, point towards ethnic differences in certain sleep measures. For instance, studies in adults reported that ethnic-minority groups, including African-Americans and Hispanics, take longer time to fall asleep and have less efficient sleep than Non-Hispanic Whites (Durrence and Lichstein, 2006, Jean-Lous et al., 2000, Lauderdale et al., 2006, Mezick et al., 2008). Also, there is evidence that African-Americans spend proportionately less time in slow-wave or deep sleep compared with Hispanics or Non-Hispanic Whites (Mezick et al., 2008, Profant et al., 2002, Rao et al., 1999, Redline et al., 2004, Stepnowsky et al., 2003). In contrast to the ethnic differences in sleep continuity disturbances and non-rapid eye movement (NREM) sleep, few studies reported variations in rapid eye movement (REM) sleep. In one investigation, Hispanics had increased phasic REM sleep compared to African-Americans and Non-Hispanic Whites (Rao et al., 1999).

The ethnic differences in sleep regulation might be associated with inherent differences in sleep homeostasis due to the interplay of biological and socio-cultural factors (Achermann et al., 1993, Carskadon et al., 2004). Alternatively, the sleep variations might suggest differential vulnerability for specific psychiatric disorders or distinct pathophysiological mechanisms. For example, African-Americans have a lower prevalence of major depressive disorder compared with Non-Hispanic Whites (Breslau et al., 2006, Williams et al., 2008). Other studies reported that African-American patients with depression had less efficient sleep and NREM sleep changes, whereas Hispanic and Non-Hispanic White patients manifested predominantly REM sleep changes although the ethnic groups were comparable on clinical symptoms and severity of depression (Giles et al., 1998b, Poland et al., 1999).

There have been even fewer investigations focusing on ethnic differences in sleep among adolescents. Significant biological and psychosocial changes in sleep and circadian regulation occur during adolescent development (Carskadon et al., 2004, Dahl, 2008). Although sleep is particularly important during brain maturation, many adolescents have insufficient sleep, and inadequate sleep is associated with a higher frequency of emotional and behavioral problems as well as impairment in social functioning (Dahl, 2008, Roberts et al., 2008, Smaldone et al., 2007). Also, evidence suggests that most adult psychiatric disorders, including anxiety, mood, addictive and psychotic disorders, have their first onset during adolescence (Kessler et al., 2005, Rapoport et al., 2005). A systematic examination of the relationships among socio-cultural factors and behavioral and physiological indices of sleep in youngsters will be helpful in understanding the cross-ethnic differences in psychopathology, without many of the potentially confounding factors that occur in adults, such as comorbid medical and psychiatric conditions.

In terms of subjective reports of sleep patterns in different ethnic groups, the findings are mixed. For example, one study reported that African-American and Hispanic youth were more likely to sleep 6 h or less per night compared with Non-Hispanic Whites (Cornelius, 1991). In contrast to this, Roberts et al. (2000) found higher frequency of hypersomnia symptoms in African-American and Mexican-American groups. In that study, Asian-American youth had the lowest prevalence of insomnia symptoms (Roberts et al., 2000). Although there are important methodological differences among studies, the emerging theme from the survey data in youth is that, after accounting for other influential factors, sleep patterns are comparable across ethnic groups (Ebin et al., 2001, Johnson and Breslau, 2001, Roberts et al., 2006). To the best of our knowledge, there are no published reports regarding ethnic differences in sleep physiology in adolescents. Given that cross-ethnic differences exist in sleep physiology among adults and that these differences may be associated with psychopathology, it is not clear when during development these differences emerge.

In this report, polysomnography measures were compared in four ethnic groups of adolescents (namely African-American, Asian-American, Mexican-American and Non-Hispanic Whites). In addition to examining ethnic differences in sleep physiology, the effects of other demographic, clinical and psychosocial factors that potentially affect sleep were evaluated. Here, ethnic determination was based on self-identified social or cultural heritage with shared physical features. The original study was not designed to examine the relationship between ethnicity and sleep patterns. The primary focus of the study was to identify pre-morbid sleep and neuroendocrine profiles associated with the development of depressive illness during prospective follow-up. Here, only baseline sleep polysomnography data are presented.