How are sleep and heart disease related?

There's an old joke among doctors that the function of sleep is to cure sleepiness. Despite an abundance of research, we still aren't sure exactly why we sleep. But we know we need to. Recent studies indicate that too much or too little sleep can be a factor in developing heart disease, just like smoking and packing on the pounds.

A 10-year study performed by Harvard University tracked the sleep habits and health of more than 70,000 women between the ages of 45 and 65 that had no previous history of heart disease. In the end, 934 of these women suffered from coronary heart disease and 271 died from it. The researchers accounted for factors like age, weight and whether they smoked, then looked at the subjects' sleep patterns. Five percent of the women slept less than five hours per night. Those women were nearly 40 percent more likely to suffer from heart disease than women who slept an average of eight hours. Women who slept more than nine hours per night were 37 percent more likely to have heart trouble.

Previous studies have shown similar results for men. Short-term sleep deprivation is known to raise blood pressure and stress hormones, lower glucose tolerance and even lead to irregular heartbeats. All of these factors are precursors to coronary disease. Chronic sleep deprivation promotes weight gain and diabetes, both of which can send you to the emergency room grabbing your chest. Going without enough sleep also affects the functioning of the lining inside the blood vessels and can cause some low-grade inflammation that could lead to heart disease.

Sleep apnea is another problem. This is a condition that makes your airway temporarily collapse when you sleep, forcing you to wake up and resume breathing. This makes for fitful sleep at best. Research has shown that people with sleep apnea also show marked increases in their blood pressure over the years. They also have a higher level of sympathetic nervous system (SNS) action. The SNS controls the heart rate and the constriction of the blood vessels. If you don't have sleep apnea, shortly after you fall asleep, your blood pressure and SNS activity will slowly fall. This can't happen when you're waking up at regular intervals to resume breathing.

If you think you're in the clear because you're a young whipper-snapper, think again. Teens that sleep less than 6.5 hours per night are more than twice as likely to get high blood pressure [source: AHA]. When you consider that teens average roughly seven hours of sleep when they require nine, it's clear that kids need to put down that Guitar Hero axe, shut off the iPhone and catch some Zs.

Now for the good news. If you want to eliminate this factor from whether you develop heart disease, all you need to do is go beddy-bye for eight hours. There are other factors, like what you eat and how much you exercise, but this one is taken care of by doing something most people love to do -- sleep. Doctors even believe that 30-minute naps a few times a week can improve your health, and many forward-thinking companies are outfitting their buildings with nap rooms.

If you have trouble sleeping, make your bedroom a haven for slumber. Paint your walls in cool blues. Ditch the TV and the laptop. Try to sleep eight hours each night -- you're doing your heart a big favor.