Sleep Duration as a Risk Factor for Incident Type 2 Diabetes in a Multiethnic Cohort
Introduction
Sleep deprivation is clearly a problem in today's society. Seven to 8 hours per night have been recommended as the optimal amount of sleep for adults, although there are variations between individuals 1, 2, 3. However, according to recent data, 71% of adults are sleeping less than 8 hours per night during the week, and the situation has gotten worse over time (1). Race/ethnic differences have also been reported with shorter sleep durations in minorities than whites 4, 5. Concurrently, an increasing prevalence and incidence of type 2 diabetes in all major ethnic groups has been observed in the United States, with a higher burden of disease among Hispanics and African Americans (AAs) than among non-Hispanic whites (NHWs) 6, 7, 8, 9.
Several epidemiologic studies of predominately NHW populations have studied the association of sleep duration with diabetes 10, 11, 12, 13, 14. However, findings have been inconsistent and ranged from finding no association 12, 13, to identifying only short sleep (12) or only long sleep as a potential risk factor (10), to finding both short and long sleep associated with incident diabetes 11, 14. Studies have also varied tremendously with respect to the level of control for diabetes risk factors and the consideration of mediating factors (14). While several studies have evaluated the role of adiposity 10, 14, insulin resistance and insulin secretion, two important predictors of diabetes 15, 16 have, to our knowledge, not been considered in this context.
We therefore aimed to evaluate the association of sleep duration and incident type 2 diabetes in the Insulin Resistance Atherosclerosis Study (IRAS), a cohort including participants of AA, Hispanic, and NHW race/ethnicity. Because IRAS included state-of-the-art measurement of both insulin sensitivity and insulin secretion from a frequently sampled intravenous glucose tolerance test conducted at baseline, we explicitly explored the role of insulin sensitivity (SI) and acute insulin response (AIR) in the context of the sleep-diabetes relationship.
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Study Design
IRAS is a multicenter cohort study of the relationships between SI, cardiovascular disease, and their risk factors, conducted in three ethnic groups. The design of IRAS has previously been described (17). The IRAS protocol was approved by local institutional review committees and all participants provided written informed consent. The baseline examination occurred between October 1992 and April 1994. A total of 1,624 persons aged 40–69 years were recruited from four clinical centers. The
Results
As shown in Table 1, sleep duration differed by race/ethnic group. The mean sleep duration was 7.1 hours per night for NHW, 6.8 hours per night for Hispanics, and 6.3 hours per night for African Americans.
Table 2 shows levels of SI and AIR and the crude incidence of type 2 diabetes across categories of sleep duration, in the total study population and by race/ethnicity. A higher SI value expresses increased insulin sensitivity. A higher AIR indicates greater insulin secretion in response to
Discussion
In this cohort of middle-aged men and women, we initially observed a U-shaped relationship between sleep duration and incident type 2 diabetes mellitus. In multivariate models, short sleep duration remained a strong and significant independent predictor of odds of diabetes among NHW and Hispanics, even after taking into account SI and AIR.
In addition to our study, three other prospective studies have shown shorter sleep duration to be predictive of diabetes. In the reports of Mallon et al. (12)
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