Waking up from napping activates hormones and mechanisms in a person's body that stops insulin from working effectively. When this occurs, it could also predispose people to Type II diabetes which may develop when the insulin a person's body makes does not work appropriately. In other words, both nighttime sleep and daytime nap duration are associated with Type II diabetes risk. In addition to unaccounted socioeconomic and lifestyle factors, the association might arise from sleep deprivation's influence on glucose metabolism.
A number of studies have discovered links between Type II diabetes risk and sleep patterns. In the year 2005, a study found that men, but not women, who reported a short sleep duration of less than or equal to 5 hours of sleep per night, or difficulty maintaining or initiating sleep were more likely to suffer from new diabetes in a 12 year follow-up. The study found that women were more prone to develop new diabetes if they reported sleeping for 9 or more hours a night. The people involved in the study were 45-65 years of age.
The relationship between sleep and diabetes risk was complicated by a study in the year 2009 that looked at nighttime sleep, daytime napping and diabetes risk independently of each other. The study found that people 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 eligible to participate in this study, people were required to be healthy and not obese. Participants who reported an hour or more of napping experienced a higher body mass index (BMI) and reported less physical activity. Interestingly, the association between daytime napping and diabetes risk persisted after statistical adjustment for the BMI and physical activity variables.
Nighttime sleep duration influenced the risk of diabetes as well. Daytime napping; however, added a twist to the results. People who participated in the study reported less than 7 hours of nighttime sleep were discovered to have an increase in diabetes risk. The relationship between sleep and diabetes risk was nonlinear for those who reported less than 7 hours of sleep. The twist is this: participants who reported more than 9 hours of nighttime sleep experienced an increased risk of diabetes onset only if they reported daytime napping of more than 1 hour.
Sleep Deprivation and Diabetes Risk
While it may be likely that unaccounted for lifestyle or socioeconomic factors explain most of the associations between sleep and diabetes risk, some evidence points to potential biological mechanisms that may play a role in the link between sleep deprivation and Type II diabetes. A study involving 11 healthy young male subjects found sleep deprivation increased glucose intolerance and insulin resistance. Following breakfast after sleep deprivation, their glucose levels were higher despite similar levels of insulin secretion. A person's brain uses up to 50% of their body's total glucose. A, 'tired,' brain resulting from sleep deprivation significantly impacts the body's glucose metabolism.
Additional factors affected by sleep have roles in glucose metabolism. During sleep debt, the levels of glucose regulating hormones such as cortisol and growth hormone are altered. Inflammatory markers known to be predisposed to insulin resistance have been demonstrated to appear due to a lack of sleep. Obstructive sleep apnea has been shown to influence a number of glucose regulators. Obstructive sleep apnea and other factors provide a positive feedback loop resulting in diabetes.
Frequent Napping Linked to Increased Risk of Type 2 Diabetes in Older Adults
Participants underwent a half-day assessment, which included a structured interview on lifestyle and medical history, and a physical examination. Self-reported frequency of napping was obtained by questionnaire, and type 2 diabetes was assessed by a fasting blood glucose sample and/or self-reports of physician diagnosis or treatment. Participants were asked to describe their napping habits and daytime sleepiness.
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Napping and Diabetes Risk
The association between napping and diabetes was unaltered even after analysis removed people with daytime tiredness or potential poor health from the results, suggesting the possibility that napping itself may increase the risk of diabetes. The investigators do note, however, that further research is needed to determine whether napping in fact plays a role in the development of Type 2 diabetes or if other factors are involved.