There's evidence that not getting enough sleep can have serious consequences. Researchers have found that a lack of sleep can promote calcium buildup in the heart arteries, leading to the plaques that can then break apart and cause heart attacks and strokes.

Researchers have documented for the first time exactly how much of a risk shortened shut-eye can be. One hour less of sleep each night, on average, can increase coronary calcium by 16 percent. Among a group of almost 500 men and women, 27 percent of those getting less than five hours of sleep each night showed plaque in their heart vessels. Only 11 percent of those sleeping five to seven hours did, and mere 6 percent of subjects sleeping more than seven hours each night showed such atherosclerosis.

While the connection between sleep and heart disease is of growing interest to researchers, earlier studies had been inconclusive, in part because most of the trials relied on people's self-reported accounts of their sleeping habits. The new study aimed to record as accurately as possible the amount of sleep that the subjects got each night. Each volunteer wore a wrist monitor that measured and recorded activity at 30 second intervals.