People who sleep less than five hours each night or more than nine hours each night have an increased chance of becoming diabetic, according to research published in Diabetes Care (February, 2003;26:380-4). Researchers kept track of over 70,000 women without diabetes for a 10-year period. Women who slept for five hours or less each night were 34% more likely to become diabetic than women who slept between seven and eight hours each night. Women who slept over nine hours each night were 35% likely to develop diabetes than the women in the seven to eight hour group.
While not sure why the connection between sleep and diabetes exist, some researchers believe that there is a connection between leptin, sleep and weight gain. In this study, women who were not overweight did not seem to have the increased diabetes risk when sleeping less. It is possible that not getting enough sleep reduces leptin levels and may therefore creates a tendency for gaining weight.
People who sleep too much tend to have poor health in general. It is possible that a number of people in the study who slept more than nine hours suffered from sleep apnea. Sleep apnea prevents restful sleep and people with sleep apnea tend to feel tired all of the time. Sleep apnea also increases diabetes risk.