Associations between long self-reported sleep, obesity and insulin resistance in a cohort of premenopausal Black and White South African women

Abstract

ObjectivesSouth African women have disproportionately high levels of overweight and obesity, and ethnic differences in obesity and insulin resistance have been observed. We investigated associations between self-reported sleep duration, obesity and insulin resistance in Black and White South African women. DesignCross-sectional. ParticipantsBlack normal-weight (n = 122), Black obese (n = 133), White normal-weight (n = 87) and White obese (n = 63) urban South African women, aged 18 to 45y. MeasurementsParticipants completed questionnaires capturing self-reported sleep duration, demographic, socioeconomic, medical history and lifestyle information. Body composition and fasting blood glucose and insulin concentrations were measured. ResultsThe Black women reported longer sleep than the White women (median: 8 h, interquartile range: 8-10 h v 7(7-8) respectively, P < .001). Adjusted models indicated that women sleeping <7 h sleep were less likely to be obese (P = .035) or insulin resistant (P = .032), while those sleeping >9 h were more likely to be insulin resistant (P = .014) than those sleeping 7 to 9 h. Shorter self-reported sleep was associated with less insulin resistance (<7 h v 7-9 h: P = .018) and longer sleep with more insulin resistance (>9 h v 7-9 h: P = .047) in the Black but not White women. ConclusionsFuture research that objectively measures sleep duration is needed to confirm these observations and investigate potential factors contributing to the relationship between sleep and risk for non-communicable diseases in different ethnic groups.