Napping and Diabetes Risk

obese or fat or overweight man napping hispanic

Nighttime sleep and daytime nap duration are associated with type 2 diabetes risk. In addition to unaccounted socioeconomic and lifestyle factors this association may arise from sleep deprivation's influence on glucose metabolism.

A several studies have found links between type 2 diabetes risk and sleep patterns. In 2005, a study found that men, but not women, who reported a short sleep duration (≤5 hours of sleep a night) or difficulty maintaining or initiating sleep were more likely to suffer from new diabetes in a 12 year follow-up (High incidence of diabetes in men with sleep complaints or short sleep duration: a 12-year follow-up study of a middle-aged population, 2005; Malton L, Broman JE, Hetta J). This study found that women were more prone to develop new diabetes if they reported sleeping for 9 or more hours a night. The study subjects were between the ages of 45 and 65.

The relationship between sleep and diabetes risk was further complicated by a 2009 study that looked at nighttime sleep, daytime napping and diabetes risk independently of each other (Day Napping and Short Night Sleeping Are Associated With Higher Risk of Diabetes in Older Adults, 2009, Qun Xu, et al.).  The study found that those who reported an hour or more of napping a day were more likely to be diagnosed with new diabetes in a 7-year follow-up medical diagnosis. To be included in the study participants had to be healthy and non-obese. Those who reported an hour or more of napping had a higher BMI and reported less physical activity. However, the association between daytime napping and diabetes risk persisted after statistical adjustment for the BMI and physical activity variables.

Like the study published in 2005, nighttime sleep duration influenced diabetes risk as well. However, daytime napping added a twist to the results.  Participants who reported less than seven hours of nighttime sleep were found to have an increase in diabetes risk. The relationship between sleep and diabetes risk was nonlinear for those reporting less than seven hours of sleep. Here is the twist: participants who reported more than nine hours of nighttime sleep had an increased risk of diabetes onset only if they reported daytime napping in excess of an hour.

It is likely that unaccounted for socioeconomic or lifestyle factors explain most of the associations between sleep and diabetes risk. However, some evidence points to potential biological mechanisms that may play a role in the link between sleep deprivation and type 2 diabetes (Reduced Sleep Duration or Quality: Relationships With Insulin Resistance and Type 2 Diabetes, 2009; Esra Tasali, Rachel Leproult, Karine Spiegel). In a study with 11 healthy young male subjects, sleep deprivation was shown to increase glucose intolerance and insulin resistance.  Following breakfast after sleep deprivation, glucose levels were higher despite similar levels of insulin secretion. The graphs below show the results of the study.

The line graphs above show the difference in glucose and insulin levels following 4-hours in bed (sleep deprivation) and 12 hours in bed (baseline).  Note the shaded area showing elevated glucose levels following breakfast after sleep deprivation.

The brain utilizes up to 50% of the body's total glucose. Therefore, a "tired" brain resulting from sleep deprivation significantly impacts the body's glucose metabolism.

Other factors affected by sleep play a role in glucose metabolism. During sleep debt, the levels of glucose regulating hormones such as growth hormone and cortisol are altered. Inflammatory markers known to be predisposed to insulin resistance have been shown to appear from a lack of sleep. Obstructive sleep apnea has been shown to influence several glucose regulators. As the image below shows, obstructive sleep apnea and other factors provide a positive-feedback loop that results in diabetes.

obstructive sleep apnea diabetes insulin resistance

Positive-feedback loop linking diabetes, OSA, sleep and glucose regulators.

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