Does lack of sleep cause diabetes?

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Epidemiologic studies of short sleep duration and glucose metabolism

Multiple cross-sectional epidemiologic studies have suggested an association between short sleep duration and diabetes, and several prospective epidemiologic studies have suggested that short sleep actually plays a causative role in diabetes.

The landmark observations of Spiegel et al11 led to a number of epidemiologic studies examining the relationships between sleep duration and sleep disturbances and diabetes risk.13

The Sleep Heart Study14 was a large, cross-sectional, community-based study of the cardiovascular consequences of sleep-disordered breathing. The authors assessed the relationship between reported sleep duration and impaired glucose tolerance or type 2 diabetes in more than 1,400 men and women who had no history of insomnia. After adjustment for age, sex, race, body habitus, and apnea-hypopnea index, the prevalence of impaired glucose tolerance and type 2 diabetes was higher in those who reported sleeping 6 hours or less per night—or 9 hours or more per night (more below about the possible effect of too much sleep on the risk of diabetes).

The major limitations of the study were that it was cross-sectional in design, sleep duration was self-reported, the reasons for sleep curtailment were unknown, and possible confounding variables as physical activity, diet, and socioeconomic status were not measured.

Knutson et al,4 in our medical center, examined the association between self-reported sleep duration and sleep quality on the one hand and hemoglobin A1c levels on the other in 161 black patients with type 2 diabetes. In patients without diabetic complications, glycemic control correlated with perceived sleep debt (calculated as the difference between self-reported actual and preferred weekday sleep duration); the authors calculated that a perceived sleep debt of 3 hours per night predicted a hemoglobin A1c value 1.1 absolute percentage points higher than the median value. The analyses controlled for age, sex, body mass index, insulin use, and the presence of major complications; it excluded patients whose sleep was frequently disrupted by pain. The effect size was comparable to (but opposite) that of oral antidiabetic drugs. However, the direction of causality cannot be confirmed from this association, as it is possible that poor glycemic control in diabetic patients could impair their ability to achieve sufficient sleep.

To date, several major prospective studies have looked at the association between short sleep duration and sleep problems and the risk of developing type 2 diabetes in adults.

The Nurses Health Study15 followed 70,000 nondiabetic women for 10 years. Compared with nurses who slept 7 to 8 hours per 24 hours, those who slept 5 hours or less had a relative risk of diabetes of 1.34 even after controlling for many covariables, such as body mass index, shift work, hypertension, exercise, and depression.

The first National Health and Nutrition Examination Survey (NHANES I)16 examined the effect of sleep duration on the risk of incident diabetes in roughly 9,000 men and women over a period of 8 to 10 years. The statistical model included body mass index and hypertension and adjusted for physical activity, depression, alcohol consumption, ethnicity, education, marital status, and age. Findings: those who slept 5 hours or less per night were significantly more likely to develop type 2 diabetes than were those who slept 7 hours per night (odds ratio 1.57, 95% confidence interval [CI] 1.11–2.22), and so were those who slept 9 or more hours per night (odds ratio 1.57, 95% CI 1.10–2.24).

Kawakami et al17 followed 2,649 Japanese men for 8 years. Those who had difficulty going to sleep and staying asleep, which are both likely to result in shorter sleep duration, had higher age-adjusted risks of developing type 2 diabetes, with hazard ratios of 2.98 and 2.23, respectively.

Björkelund et al18 followed 6,599 nondiabetic Swedish men for an average of 15 years. Self-reported difficulty sleeping predicted the development of diabetes with an odds ratio of 1.52 even after controlling for age, body mass index at screening, changes in body mass index at follow-up, baseline glucose level, follow-up time, physical activity, family history of type 2 diabetes, smoking, social class, and alcohol intake.19

Interestingly, the authors found that the resting heart rate was higher at baseline in the men who later developed diabetes. This finding could be interpreted as reflecting greater sympathetic nervous system activity, a putative mediator of the metabolic dysfunction associated with both short sleep duration and obstructive sleep apnea.20,21

Meisinger et al,22 in a study of more than 8,000 nondiabetic German men and women 25 to 74 years old, found a hazard ratio of developing diabetes of 1.60 (95% CI 1.05–2.45) in men and 1.98 (95% CI 1.20–3.29) in women who reported difficulty staying asleep, who thus would have shortened sleep duration. This effect was independent of other risk factors for diabetes.

Yaggi et al,23 in a prospective study of 1,139 US men, also found a U-shaped relationship between sleep duration and the incidence of diabetes, with higher rates in people who slept less than 5 or more than 8 hours per night.

Cappuccio et al24 performed a meta-analysis of all the prospective studies published to date. Their review included 10 prospective studies, with 107,756 participants followed for a median of 9.5 years. Sleep duration and sleep disturbances were self-reported in all the studies. They calculated that the risk of developing diabetes was 28% higher with short sleep duration (≤ 5 or < 6 hours in the different studies), 48% higher with long sleep duration (> 8 hours), 57% higher with difficulty going to sleep, and 84% higher with difficulty staying asleep.

Limitations of these studies. A consideration when trying to interpret the relationship between length of sleep and the incidence of diabetes is that sleep duration in these studies was self-reported, not measured. If a patient reports sleeping more than 8 hours per night, it could mean that he or she is not truly getting so much sleep, but rather is spending more time in bed trying to sleep.

Another possibility is that the higher incidence of type 2 diabetes in people who slept longer is due to undiagnosed obstructive sleep apnea, which is associated with daytime sleepiness and possibly longer sleep time to compensate for inefficient sleep.

Finally, depressive symptoms, unemployment, a low level of physical activity, and undiagnosed health conditions have all been associated with long sleep duration and could affect the relationship with diabetes risk.

In summary, epidemiologic studies from different geographic locations have consistently indicated that short sleep or poor sleep may increase the risk of developing type 2 diabetes mellitus and suggest that such an association spans different countries, cultures, and ethnic groups.

Therefore, there is a need for additional prospective epidemiologic studies that use objective measures of sleep. Furthermore, studies need to determine whether the cause of sleep restriction (eg, insomnia vs lifestyle choice) affects this relationship. Randomized, controlled, interventional studies would also be useful to determine whether lengthening sleep duration affects the development of impaired glucose tolerance or type 2 diabetes mellitus.

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