Associations between long self-reported sleep, obesity and insulin resistance in a cohort of premenopausal Black and White South African women Dale E. Rae, PhD a, ⁎, Paula R. Pienaar, MSc a , Rob H.P. Henst, MSc a , Laura C. Roden, PhD b , Julia H. Goedecke, PhD a, c a Division of Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa b Department of Molecular and Cell Biology, Faculty of Science, University of Cape Town, Cape Town, South Africa c Non-communicable Diseases Research Unit, South African Medical Research Council, Cape Town, South Africa abstract article info Article history: Received 15 December 2017 Received in revised form 27 June 2018 Accepted 6 August 2018 Available online xxxx Keywords: Self-reported sleep duration Body mass index Ethnicity Non-communicable disease Type 2 diabetes mellitus Socioeconomic Objectives: South 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. Design: Cross-sectional. Participants: Black 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. Measurements: Participants completed questionnaires capturing self-reported sleep duration, demo- graphic, socioeconomic, medical history and lifestyle information. Body composition and fasting blood glucose and insulin concentrations were measured. Results: The Black women reported longer sleep than the White women (median: 8 h, interquartile range: 8-10 h v 7(7-8) respectively, P b .001). Adjusted models indicated that women sleeping b7 h sleep were less likely to be obese (P = .035) or insulin resistant (P = .032), while those sleeping N9 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 (b7 h v 7-9 h: P = .018) and longer sleep with more insulin resistance (N9 h v 7-9 h: P = .047) in the Black but not White women. Conclusions: Future research that objectively measures sleep duration is needed to confirm these ob- servations and investigate potential factors contributing to the relationship between sleep and risk for non-communicable diseases in different ethnic groups. © 2018 National Sleep Foundation. Published by Elsevier Inc. All rights reserved. Introduction Historically, infectious diseases such as human immunodeficiency virus (HIV) and tuberculosis have represented the primary disease burden in South Africa. A recent shift, has meant that non- communicable diseases (NCDs) now account for 56% of all deaths annually. 1 Within South Africa, type 2 diabetes mellitus (T2DM) is the second most common cause of death (5.4%) after tuberculosis (7.2%), and was the leading cause of death in South African women (7.1%) in 2015. 1 The prevalence of T2DM in South African urban Black women has increased by 53% over the past 20 years, and repre- sents the highest reported increase of T2DM prevalence in sub- Saharan Africa. 2 The increasing T2DM prevalence may be attributed to the high levels of insulin resistance 3–5 and obesity, 6 particularly in women. Indeed, results from the latest national survey show that more than 65% of South African women are overweight or obese. 7 Furthermore, there appear to be ethnic differences in obesity and in- sulin resistance in South African women, with the Black women hav- ing higher levels of obesity 8 and insulin resistance than the White women. 5,9 Sleep Health xxx (xxxx) xxx–xxx Abbreviations: BMI, body mass index; HOMA-IR, homeostatic model assessment of insulin resistance; MVPA, moderate and vigorous physical activity; NCD, non- communicable disease; SES, socioeconomic status; T2DM, type 2 diabetes mellitus; WC, waist circumference. ⁎ Corresponding author at: Division of Exercise Science and Sports Medicine, De- partment of Human Biology, Faculty of Health Sciences, University of Cape Town, PO Box 115, Newlands, Cape Town, South Africa, 7725. Tel.: +27 21 650 4577. E-mail address: Dale.Rae@uct.ac.za (D.E. Rae). SLEH-00308; No of Pages 7 https://doi.org/10.1016/j.sleh.2018.08.005 2352-7218/© 2018 National Sleep Foundation. Published by Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Sleep Health Journal of the National Sleep Foundation journal homepage: sleephealthjournal.org Please cite this article as: Rae DE, et al, Associations between long self-reported sleep, obesity and insulin resistance in a cohort of premen- opausal black and white south African women, Sleep Health (2018), https://doi.org/10.1016/j.sleh.2018.08.005