Everyone knows that a good night’s sleep can make you feel better, but two new studies find that sleeping too little or too much can be deadly. Recent research by two doctors in Boston found that people who sleep seven to eight hours a night may live longer.

　　After studying 4,541 people, Dr. Daniel Gottlieb from the Boston Univers

ity School of Medicine, found that people who slept six hours or less a night had a 50 percent higher chance of dying over a 14-year period. Suprisingly, people who slept for nine hours or more were 70 percent more likely to die during the same time period.

　　“We recommend a lot of lifestyle changes and medications for risks smaller than this,”he said.“Cigarette smoking is associated with a 50 percent excess mortality risk; sleeping less than six hours is also associated with a 50 percent mortality risk.”

　　Dr. Najib Ayas, who teaches at Harvard Medical School, found similar results after studying 71,167 women. He discovered that women who slept five hours or less per night were 39 percent more likely to have a heart attack over a 10 year period. Women who slept more than nine hours a night had a 37 percent higher chance.

　　While it’s no surprise to sleep experts that too little sleep causes health problems, the doctors are unsure why too much sleep would also pose risks.

　　“I have a gut feeling some disorder is fragmenting their sleep their sleep,”said Ayas.“When people say they sleep nine or 10 hours a day, often something is wrong with their sleep.”