The Donut Hole of Sleep Duration Mortality
The study provides unequivocal evidence of the direct link between both short (less than 6 hours sleep a night) and long (9 hours or more) duration of sleep and an increased chance of dying prematurely, compared to those who sleep 6-8 hours a night on average.
Increased mortality from getting too much sleep appeared to be due to an increased risk of other co-morbidities (sleep apnea from morbid obesity?) that both increase sleep behavior and increase mortality but apparently the increase in death from getting too little sleep remained after other potential health conditions associated with sleep reduction were factored out. This is plausible since lack of sleep increases stress hormone release which could increase the risk of atherosclerotic disease and future cardiovascular events such as a heart attack or stroke.
Be aware, however, that this is only a 12% increase in premature death over a 25 year span and only pertains to people sleeping fewer than 6 hours per night.