Abstract
There are differences in sleep duration between Blacks/African-Americans and Whites/European-Americans. Recently, we found differences between these ancestry groups in the circadian system, such as circadian period and the magnitude of phase shifts. Here we document the role of ancestry on sleep and cognitive performance before and after a 9-h advance in the sleep/wake schedule similar to flying east or having a large advance in sleep times due to shiftwork, both of which produce extreme circadian misalignment. Non-Hispanic African and European-Americans (N = 20 and 17 respectively, aged 21–43 years) were scheduled to four baseline days each with 8 h time in bed based on their habitual sleep schedule. This sleep/wake schedule was then advanced 9 h earlier for three days. Sleep was monitored using actigraphy. During the last two baseline/aligned days and the first two advanced/misaligned days, beginning 2 h after waking, cognitive performance was measured every 3 h using the Automated Neuropsychological Assessment Metrics (ANAM) test battery. Mixed model ANOVAs assessed the effects of ancestry (African-American or European-American) and condition (baseline/aligned or advanced/misaligned) on sleep and cognitive performance. There was decreased sleep and impaired performance in both ancestry groups during the advanced/misaligned days compared to the baseline/aligned days. In addition, African-Americans obtained less sleep than European-Americans, especially on the first two days of circadian misalignment. Cognitive performance did not differ between African-Americans and European-Americans during baseline days. During the two advanced/misaligned days, however, African-Americans tended to perform slightly worse compared to European-Americans, particularly at times corresponding to the end of the baseline sleep episodes. Advancing the sleep/wake schedule, creating extreme circadian misalignment, had a greater impact on the sleep of African-Americans than European-Americans. Ancestry differences in sleep appear to be exacerbated when the sleep/wake schedule is advanced, which may have implications for individuals undertaking shiftwork and transmeridian travel.
Highlights
There is increasing evidence that there are differences in sleep duration between groups with different evolutionary ancestry [1, 2]
dim light melatonin onset (DLMO) and temperature minimum (Tmin) were in a normal phase relationship to sleep after the four baseline days; DLMOs occurred before scheduled bedtime for all but one participant and estimated Tmins all occurred within the sleep episode (Fig 2, top panel)
Sleep was shorter during advanced/misaligned days compared to baseline/aligned days, and shorter for African-Americans compared to European-Americans (Table 3)
Summary
There is increasing evidence that there are differences in sleep duration between groups with different evolutionary ancestry [1, 2]. More recent evidence from our laboratory demonstrates that there are differences between African-Americans and European-Americans in the way the circadian timing system phase shifts in response to a large abrupt advance shift in the sleep/wake (and light-dark) schedule [23, 26]. The shorter sleep experienced by African-Americans under normal circumstances [3, 5, 6] may subsequently result in cognitive performance impairments such as decreased reaction time, increased sleepiness, and mood, especially if sleep is restricted over several days [28,29,30]. There has been extensive research into the effects of shifted sleep on cognitive performance [38,39,40,41,42,43,44,45], it is unknown if shifting the sleep/wake schedule has different effects on performance in African-Americans compared to European-Americans. Americans during advanced/misaligned days, as a shorter circadian period facilitates phase advances [23, 26]
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