pii: sp-00356-15
http://dx.doi.org/10.5665/sleep.4876
EDITORIAL
Parsing Race by Genetic Ancestry Commentary on Halder et al. African genetic ancestry is associated with sleep depth in older African Americans. SLEEP 2015;38:1185–1193. Namni Goel, PhD Division of Sleep and Chronobiology, Unit for Experimental Psychiatry, Department of Psychiatry, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA
The investigation of race differences, particularly between Caucasians and African Americans, is a critical and continually growing area in the sleep field. Indeed, scientific interest in this topic began accelerating in the early 2000s1 and has continued its upward trend over the past decade. Studies measuring objective sleep have found decreases in slow wave sleep (SWS) and increases in stage 1 and 2 NREM sleep in African Americans compared to Caucasians.2–6 Sleep duration has also been reported to be shorter, and sleep efficiency and subjective sleep quality lower in African Americans than Caucasians.6–9 Population-based studies also have reported race differences using subjective self-reported sleep10–13 or wrist actigraphy,14 whereby African Americans are more likely to sleep less than Caucasians. Moreover, epidemiologic studies have shown the relationship between self-reported short sleep duration and obesity is stronger in African Americans.15,16 Laboratory studies support this relationship: when exposed to experimental chronic sleep restriction, African Americans respond differently from Caucasians in various energy balance measures, including gaining more weight, increasing carbohydrate intake and displaying lower resting metabolic rates.17–19 Notably, all of these studies defined race purely by self-identification. The article by Halder and colleagues20 in this issue of SLEEP parses the concept of race by determining it via genetic ancestry—a significant step forward for future studies investigating race differences in our field. Halder et al.20 utilized genetic ancestry to determine the mechanisms underlying the aforementioned race differences in sleep characteristics—specifically whether genetic factors, including genes inherited differentially from ancestors, rather than social and/or psychological processes,7 were mediators of these differences. The study employed a communitybased sample of 70 African American (mean age of 59.5 y) and 101 Caucasian/European-American (mean age of 60.5 y) older men and women. The individual percentage of African ancestry in African Americans was measured in blood using a panel of 1,698 ancestry informative genetic markers and ranged from 10% to 88% (mean of 67%)—a wide range typically expected for a genetically admixed population.20 In-home
Submitted for publication June 2015 Accepted for publication June 2015 Address correspondence to: Namni Goel, PhD, Division of Sleep and Chronobiology, Unit for Experimental Psychiatry, Department of Psychiatry, University of Pennsylvania Perelman School of Medicine, 1017 Blockley Hall, 423 Guardian Drive, Philadelphia, PA 19104-6021; Tel: (215) 898-1742; Fax: (215) 573-6410; Email:
[email protected] SLEEP, Vol. 38, No. 8, 2015
polysomnographic measures of sleep duration, sleep efficiency, and indices of sleep depth including percent visually scored SWS and NREM EEG delta power were used as the primary sleep phenotypes.20 The authors hypothesized racial differences in sleep phenotypes would associate with individual genetic ancestry in African Americans. As was true for prior studies,2–9 sleep duration, efficiency, and SWS percent differed significantly by self-identified race. The authors then examined these phenotypes using genetic ancestry. They found a higher percentage of African ancestry was associated with lower percent SWS in African Americans and explained 11% of the variation in SWS after adjusting for various covariates. Similarly, a higher percentage of African ancestry was associated with lower NREM EEG delta power and explained 10% of the variation in delta power. No such associations were observed for sleep duration or sleep efficiency. The results of this study indicate African Americans have inherited multiple alleles (either few alleles of large effect sizes or several alleles of moderate to low effect sizes) from their African ancestry that predispose them to less SWS and delta power.20 The authors conclude that racial differences in SWS and delta power, but not in sleep duration or sleep efficiency, in older adults are partly moderated by genetic variation related to African genetic ancestry in African Americans. Future studies are needed to determine (1) specific loci that may underlie the genetic ancestry-SWS and genetic ancestry-delta power relationships, and (2) whether reported findings are generalizable to other populations who have SWS and delta power that differ from older adults, including young or middle-aged adults or those who have sleep disorders such as insomnia or sleep apnea. Importantly—and as acknowledged by the authors—the absence of genetic ancestry markers in prior studies investigating race differences does not undermine their findings, since they did not aim to investigate genetic components or mechanisms. In such cases, self-identification of race is sufficient. Indeed, in the Halder et al. study,20 the high percentage of African ancestry in African Americans suggests that self-identification is a reasonably accurate method to categorize race. Of interest, Halder et al.’s genetic ancestry method used more markers (1,698 vs. 176) than a 2015 circadian rhythm study by Eastman and colleagues,21 although that study also used participant-reported race of parents and grandparents to determine ancestry. Eastman and colleagues found robust differences between African Americans and Caucasians in basic properties of the circadian clock, including endogenous period (tau) and the magnitude of phase advances and delays, using
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genetic ancestry,21 as well as with self-identification techniques.22,23 While it remains to be determined if one version of this technique is superior to the other, both clearly show success in using genetic ancestry to determine the percentage admixture in African Americans, which ranges from 12% to 23% across various regions in the United States (reviewed in21). Since the genetic aspects of race can be parsed from the cultural, behavioral, and social aspects that may underlie observed phenotypic differences, genetic ancestry is the ideal method for future studies in the sleep and circadian rhythm fields involving races with significant, recent large scale continental admixture such as African Americans. CITATION Goel N. Parsing race 2015;38(8):1151–1152.
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ancestry.
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DISCLOSURE STATEMENT The preparation of this commentary was supported by ONR N00014-11-1-0361 and NASA NNX14AN49G. Dr. Goel has indicated no financial conflicts of interest. REFERENCES
1. Durrence HH, Lichstein KL. The sleep of African Americans: a comparative review. Behav Sleep Med 2006;4:29–44. 2. Rao U, Poland RE, Lutchmansingh P, Ott GE, McCracken JT, Lin KM. Relationship between ethnicity and sleep patterns in normal controls: implications for psychopathology and treatment. J Psychiatr Res 1999;33:419–26. 3. Profant J, Ancoli-Israel S, Dimsdale JE. Are there ethnic differences in sleep architecture? Am J Hum Biol 2002;14:321–26. 4. Stepnowsky CJ Jr, Moore PJ, Dimsdale JE. Effect of ethnicity on sleep: complexities for epidemiologic research. Sleep 2003;26:329–32. 5. Thomas KS, Bardwell WA, Ancoli-Israel S, Dimsdale JE. The toll of ethnic discrimination on sleep architecture and fatigue. Health Psychol 2006;25:635–42. 6. Mezick EJ, Matthews KA, Hall M, et al. Influence of race and socioeconomic status on sleep: Pittsburgh SleepSCORE project. Psychosom Med 2008;70:410–16. 7. Ruiter ME, Decoster J, Jacobs L, Lichstein KL. Normal sleep in African-Americans and Caucasian-Americans: a meta-analysis. Sleep Med 2011;12:209–14.
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8. Adenekan B, Pandey A, McKenzie S, Zizi F, Casimir GJ, Jean-Louis G. Sleep in America: role of racial/ethnic differences. Sleep Med Rev 2013;17:255–62. 9. Hall MH, Matthews KA, Kravitz HM, et al. Race and financial strain are independent correlates of sleep in midlife women: the SWAN sleep study. Sleep 2009;32:73–82. 10. Singh M, Drake CL, Roehrs T, Hudgel DW, Roth T. The association between obesity and short sleep duration: a population-based study. J Clin Sleep Med 2005;1:357–63. 11. Hale L, Do DP. Racial differences in self-reports of sleep duration in a population-based study. Sleep 2007;30:1096–103. 12. Nunes J, Jean-Louis G, Zizi F, et al. Sleep duration among black and white Americans: results of the National Health Interview Survey. J Natl Med Assoc 2008;100:317–22. 13. Whinnery J, Jackson N, Rattanaumpawan P, Grandner MA. Short and long sleep duration associated with race/ethnicity, sociodemographics, and socioeconomic position. Sleep 2014;37:601–11. 14. Lauderdale DS, Knutson KL, Yan LL, et al. Objectively measured sleep characteristics among early-middle-aged adults: the CARDIA study. Am J Epidemiol 2006;164:5–16. 15. Donat M, Brown C, Williams N, et al. Linking sleep duration and obesity among black and white US adults. Clin Pract 2013;10:10.2217/ cpr.13.47. 16. Grandner MA, Chakravorty S, Perlis ML, Oliver L, Gurubhagavatula I. Habitual sleep duration associated with self-reported and objectively determined cardiometabolic risk factors. Sleep Med 2014;15:42–50. 17. Spaeth AM, Dinges DF, Goel N. Effects of experimental sleep restriction on weight gain, caloric intake, and meal timing in healthy adults. Sleep 2013;36:981–90. 18. Spaeth AM, Dinges DF, Goel N. Sex and race differences in caloric intake during sleep restriction in healthy adults. Am J Clin Nutr 2014;100:559–66. 19. Spaeth AM, Dinges DF, Goel N. Resting metabolic rate varies by race and by sleep duration. Obesity. In Press. 20. Halder I, Matthews K, Buysse D, et al. African genetic ancestry is associated with sleep depth in older African Americans. Sleep 2015;38:1185–93. 21. Eastman CI, Suh C, Tomaka VA, Crowley SJ. Circadian rhythm phase shifts and endogenous free-running circadian period differ between African-Americans and European-Americans. Sci Rep 2015;5:8381. 22. Smith MR, Burgess HJ, Fogg LF, Eastman CI. Racial differences in the human endogenous circadian period. PLoS One 2009;4:e6014. 23. Eastman CI, Molina TA, Dziepak ME, Smith MR. Blacks (African Americans) have shorter free-running circadian periods than whites (Caucasian Americans). Chronobiol Int 2012;29:1072–7.
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