For many years, the recommended amount of sleep an adult needs to stay healthy is eight hours per night. But new research is finding that slightly less is actually optimal, particularly when it comes to reducing the risk of developing cardiovascular disease.

The original "eight-hours-a-night" recommendation came from a study conducted by Dr. Thomas Wehr at the National Institutes of Health. The findings were not necessarily based on health effects, but on the observation that people appeared to be "biologically programmed" to sleep about 8.25 hours a night.

The latest study was conducted by doctors at the West Virginia University School of Medicine. The researchers analyzed data from more than 30,000 adults who participated in the 2005 National Health Interview Survey. They found that those who slept five total hours per day had more than twice the risk of suffering from coronary heart disease, heart attack, angina, or stroke than those who slept a total of seven hours each day.

But more isn't always better. The doctors also found that those who slept nine hours or more each day also had an elevated risk of cardiovascular disease.

Sleep duration affects both endocrine and metabolic functions. A study by Dr. Eve Van Cauter at the University of Chicago found that healthy adults who got only four hours of sleep a night had an impaired ability to process sugar, leading them to an increased risk for diabetes or obesity — both risk factors for cardiovascular disease. Sleep deprivation can also lead to reduced insulin sensitivity and elevated blood pressure, which can increase the risk of hardening of the arteries.

Chronic insomnia is the most common sleep complaint among Americans. According to the National Center for Sleep Disorders Research, about 30 to 40 percent of adults say they have had some symptoms of insomnia within the past year. Women and older adults appear to be at greatest risk.

WebMD offers the following tips to help you get a good night's sleep tonight:

1. Cut out the caffeine, particularly in the afternoon and evening. The effects of caffeine can take up to eight hours to wear off, so stop drinking coffee, teas or colas (or eating chocolate) at least four to six hours before bedtime.

2. Avoid alcohol and tobacco. Alcohol may initially help you to fall asleep, but often causes disturbances during the sleep cycle. Nicotine in tobacco products act as a stimulant similar to caffeine and can keep you from falling or staying asleep.

3. Try a stress reducing exercise or ritual before going to bed. About half of people who experience insomnia blame the problem on stress or worry. Try meditation, prayer, light stretching or gentle yoga, or a hot bath to help you relax. A journal by the bed may also help. By writing down your worries, you get them out of your head, making you less likely to obsess.

4. Keep the bedroom quiet, dark and comfortable. The ideal room temperature for sleeping is between 59 and 71 degrees F. Turn off all light-producing objects in the bedroom (laptops, TV's, or nightstand lamps). Some people often find that scents such as lavender or sandlewood help promote sleep.

5. Eat right. Eating a high-fat meal, and then laying down, is a recipe for heartburn. Don't go to bed hungry, but avoid heavy meals right before bedtime. You may also try foods that contain tryptophan (in small portions) before bedtime, such as milk, tuna, turkey, artichokes, avocados, almonds, walnuts, or bananas. If you have a problem with waking to use the bathroom at night, avoid fluids after 8pm.