The risk is 2 times higher for people who sleep less than 7 hours or more than 8 hours a night. The findings were published recently on the website of the journal Sleep Medicine.

The researchers arrived at this conclusion after analyzing the life habits of 276 subjects over a 6-year period. They determined that over this timespan, approximately 20% of those with long and short sleep duration developed type 2 diabetes or impaired glucose tolerance versus only 7% among subjects who were average duration sleepers. Even after taking into account the effect attributable to differences in body mass among the subjects, the risk of diabetes and insulin resistance was still twice as high among those with longer and shorter sleep duration than average sleepers.

The researchers also point out that diabetes is not the only risk associated with sleep duration. A growing number of studies have shed light on a similar relationship between sleep and obesity, cardiovascular disease, and overall mortality. The authors observe that among adults, between 7 and 8 hours of nighttime sleep appears to be the optimum duration to protect against common diseases and premature death.

However, it seems that fewer and fewer people sleep the optimum number of hours. A survey conducted in 1960 showed that American adults slept an average of 8 to 8.9 hours a night. By 1995, that average had dropped to 7 hours. A study conducted in 2004 by the National Center for Health Statistics found that one-third of adults aged 30 to 64 slept less than 6 hours a night.

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Dr. Suglia and her team examined the impact of exposure to community violence on physiological markers of stress response in children. More specifically, they looked at the influence of post-traumatic stress symptoms (e.g. difficulty with attention or sleep, intrusive thoughts, flashbacks, worries) on the daily cortisol response among 28 girls and 15 boys aged 7-13 years old. Mothers rated their child's exposure to community violence (e.g. hearing gunshots, witnessing or experiencing shoving, hitting, punching, knife attacks, shootings) and the resulting post-traumatic stress symptoms. The researchers also collected saliva samples from the children four times a day over three days to measure cortisol production over the course of the day.

They found a link between exposure to community violence and a disruption to the stress pathways in the body. In particular, the higher children scored on the stress symptoms, the greater the disruption to their cortisol production pattern and the higher their cortisol levels over the course of the day, especially in the afternoon and evening.

Dr. Shakira Franco Suglia concludes: "Our study indicates that important biological effects occur in children living in high-crime neighborhoods, although with less severe distress symptoms than those experienced by children diagnosed with post-traumatic stress disorder. As a result, they may not come to the attention of healthcare providers and a large number of children may be impacted with broad adverse health effects."

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