When it comes to sleep, the lucky number is seven.

A new study finds that people who sleep seven hours a night have a lower risk for common health problems. And if you're not getting enough Zs, you're putting yourself at risk for illness, disease and possibly even an early death.

If you manage to sleep much longer than that, you probably consider yourself lucky (and you probably don't have children in your home). But don't get too comfortable as you count your sheep--because too much sleep also comes with a disease risk.

Sometimes, you just can't win... even in your own bed.

Researchers looked at data on more than 30,000 adults, and found that those who slept less than five hours a day had double the risk of angina, heart disease, heart attack or stroke overall.

The researcher say adults younger than 60 who slept for five hours a night or less had triple the risk of cardiovascular disease when compared to those who got that lucky seven. Women who slept five hours or less had 2.5 times the risk.

The study published in the journal Sleep also found that people who slept for nine or more hours had 1.5 times the risk of cardiovascular disease as those who slept for seven hours a night. People who slept the most also faced an increased risk of heart attack and stroke.

What's more, the West Virginia University researchers say these associations held even after they adjusted for factors like age, weight, physical activity and smoking.

In fact, even after they removed all the patients with diabetes, high blood pressure or depression, they found that too much or too little sleep was still associated with a significant boost in risk.

Like everything else in life, sleep is a balance.

Meanwhile, another new study finds that people who don't get enough sleep throughout the week can make up for it with one single marathon snooze session.

University of Pennsylvania researchers looked at 142 adults who got four hours of sleep a night for five nights, and found what you've probably experienced yourself if you've been through a period like that: The lost sleep made them slow and unfocused.

The researchers didn't say, but I'm willing to bet these sleepless subjects were more than a little bit cranky, too. But after one night where they were allowed to sleep for 10 hours, the subjects were back in the land of the fully alert.

So while that's good news for anyone who needs to catch up after a bad week, just remember the first study--because regularly missing out on sleep won't just make you tired and groggy.

It can actually kill you.