Chronotype indicates a person's "circadian preference," that is, the time of day when they prefer to perform certain activities (e.g. a "morning" vs "evening" person). Sleep timing is related to chronotype but is also constrained by social requirements. When sleep timing does not align with chronotype, circadian disruption can occur, and circadian disruption impairs cardiometabolic health. There are well-known racial disparities in cardiometabolic health whereby Black adults are at higher risk. It is not well-known, however, whether sleep timing within each chronotype varies between Black and White adults, which was the focus of these analyses. These data are from a cross-sectional sleep study conducted in 2020 to 2023 as an ancillary to the Coronary Artery Risk Development in Young Adults (CARDIA) cohort study, in the United States. The Morningness-Eveningness Questionnaire (MEQ) captured chronotype in 2,373 participants aged 52-70 years. Chronotype was based on both overall MEQ score and question 19 categories. A subset of participants wore a wrist actigraphy monitor for ~7 days to assess sleep timing ( = 720). Our sample included 27% Black women, 17% Black men, 33% White women, and 24% White men. Mean MEQ score and chronotype distribution did not differ among race-gender groups. Among morning types, Black women and men had a later sleep start and midpoint than White women (23-34 minutes later for Black women, 32-53 minutes for Black men). Among intermediate types, Black women had significantly later sleep start (55 minutes later) and midpoint (44 minutes later), and Black men had a later sleep start (50 minutes later) than White women adjusting for age and study site. In summary, regardless of chronotype, Black adults had later sleep timing than White adults. n
