Sleep duration and mortality
A survey of 1.1 million residents in America found that those who slept 7.5 hours or more had an increased rate of mortality whereas those who slept 6 hours or less had a reduced mortality ratio. Getting 8.5 or more hours of sleep per night increases the mortality rate by 15%. Severe insomnia - less than 3.5 hours in women and 4.5 hours in men - leads to a 15% increase in mortality. However, most of the increase in mortality from severe insomnia was discounted after controlling for comorbid disorders. After controlling for sleep duration and insomnia, use of sleeping pills was also found to be associated with an increased mortality rate. The lowest mortality was seen in individuals who slept between six and a half and seven and a half hours per night. Even sleeping only 4.5 hours per night is associated with very little increase in mortality. Thus mild to moderate insomnia for most people may actually increase longevity and severe insomnia has only a very small effect on mortality. As long as a patient refrains from using sleeping pills there is little to no increase in mortality associated with insomnia but there does appear to be an increase in longevity. This is reassuring for patients with insomnia in that despite the sometimes unpleasantness of insomnia, insomnia itself appears to be associated with increased longevity. It is unclear why sleeping longer than 7.5 hours is associated with excess mortality.
However, insufficient sleep is also linked directly to heart disease, so take this with a grain of salt.