Seven Hours

It turns out the optimal number of hours of sleep for adults is just seven. Not eight. Not nine. At least, that is, if you're interested in decreasing your likelihood of a heart attack.

A study by University of West Virginia researchers, published in the peer-reviewed journal Sleep, found that people who get five hours of sleep were up to three times as likely to develop cardiovascular disease than people who got seven hours.

But less expected, people who got nine hours or more were one-and-a-half times as likely to.

The WVU study analyzed data from 30,000 adults in the year 2005, and adjusted for factors such as age, sex, race, weight and activity level.

A separate study, published in the same issue of Sleep, found that while the type of sleep deprivation often experienced by adults during the work week definitely causes slower reaction times and trouble focusing, an extra-long night of sleep (up to 10 hours) on the weekend really does improve alertness.

But no word on what yoyoing between five hours a night during the week and ten hours on the weekend does to your heart.