Sleep is essential for good health, and too little of it may shorten your life, according to one study. REM (rapid eye movement) sleep is when dreams occur and the body repairs itself. For every 5 percent reduction in REM sleep, mortality rates increase 13 percent to 17 percent among older and middle-age adults.

The study followed more than 2,600 men, average age 76, for a median of 12 years. Researchers also collected data on nearly 1,400 men and women, average age 52, who were part of another study and were followed for a median of 21 years.

In both groups, poor REM sleep was tied to early death from any cause as well as death from cardiovascular and other diseases. This shows that it’s not just total sleep time that’s important, but the right balance of the different stages of sleep.