Zuraikat et al. (1) conducted a randomized clinical trial to examine the association between chronic insufficient sleep and type 2 diabetes in women. Shorter sleep duration with sleep restriction (SR) of 1.5 h/night increased the risk of type 2 diabetes, which was observed by reduced insulin sensitivity. Habitual total sleep time of 7–9 h/night was set as a control by actigraphy. Fasting serum insulin and homeostasis model assessment of insulin resistance were significantly increased with SR versus adequate sleep, which were predominant in postmenopausal women. Changes in adiposity did not mediate the effects of SR on reduced insulin sensitivity. I have some concerns about the study.
First, based on a 6-week trial, the authors considered that insufficient sleep, which was defined by shorter sleep duration, could be a modifiable risk factor for type 2 diabetes, especially in postmenopausal women. Moreover, sleep debt was not maintained for long enough to detect incident type 2 diabetes. Insufficient sleep with SR may not directly relate to chronic insomnia and sleep disorder. Sleep is a fundamental lifestyle factor and closely connects with several type 2 diabetes–related factors. Although the investigators adjusted for adiposity, a complicated causal relationship cannot be easily adjusted statistically.
Second, postmenopausal women had diminished insulin sensitivity and hormonal and aging factors may contribute to clinical outcomes. Duan et al. (2) reviewed the effect of sleep deprivation on subsequent risk of type 2 diabetes. Insufficient sleep was classified into total and partial sleep deprivations and induced a trend of weight gain due to increased energy intake with the additional energy expenditure of nocturnal wakefulness, leading to adverse glucose metabolism. A trial by Zuraikat et al. was categorized as partial sleep deprivation, and most clinical trials failed to show the statistical difference. In this review, insomnia was significantly associated with adverse glucose outcomes, although it is difficult to isolate the effects of insomnia on metabolic outcomes independent of comorbidities and insufficient sleep. In particular, the causal association among insufficient sleep, insomnia, adiposity, and risk of type 2 diabetes may be difficult to confirm.
Finally, a relatively longer SR period may be related to the increased risk of glucose metabolism (3), and circadian disruption relates to the risk of diabetes (4). There are meta-analyses that present the significant relationship between insufficient sleep and reduced insulin sensitivity (5). As the number of studies for meta-analyses is limited, the risk in postmenopausal women cannot be estimated stably. Additional clinical trials may be important to specify the relationship, including participants with different ethnicities and socioeconomic status.
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Duality of Interest. No potential conflicts of interest relevant to this article were reported.
