This letter follows up on an article recently published in the Journal of Biological Rhythms. The authors of the original article used actigraphy data from a sample of 720 participants to show that the mean chronotype of male participants is not only significantly different from the mean chronotype of female participants but also that the mean chronotype of Black participants is about 20 min later than the mean chronotype of White participants. I reached the same conclusions using a larger data set of 7562 participants from National Health and Nutrition Examination Survey (NHANES) 2013-2014. This corroboration is important because the associations of race and gender with chronotype have been inconsistent in studies in which chronotype was measured with questionnaires rather than with objective rest-activity measures.
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