According to sleep researchers people who sleep for more or less than seven hours a night have increased mortality rates. A study of over one million adults conducted over a six year time period shows that the old advice that you need eight hours sleep a night might need modifying. Looking at the length of time people sleep and its relationship to life expectancy, researchers at the University of Texas, and colleagues, find that seven hours is the optimum.
People who sleep for eight hours or longer, or less than four hours a night, have a significantly increased death rate. Insomnia does not appear to be a risk, but those who took sleeping pills were more likely to die sooner. It is not clear why sleep has this effect upon mortality, although the highest risk seemed to be linked to sleeping longer, rather than shorter, hours. More needs to be done to work out why long sleep is risky - in the meantime, you can get away with six or seven hours knowing you're doing no damage to your long-term health.