Do you believe you get enough sleep? If you're like many of the people , you may not. Even more troubling, individuals are getting less shut-eye than they really think.

"People don't get enough sleep, and they get less sleep than they think," says Dr. Diane S. Lauderdale, a health studies expert at the University of Chicago. "As we learn more and more about the importance of sleep for health, we find evidence that people seem to be sleeping less and less."

Lauderdale and her team followed over the long haul  nearly 670 38- to 50-year-olds, who wore movement detectors on their wrists and kept sleep journals. Lauderdale measured how long they slept, how long they needed to fall asleep and how much time they spent in bed.

Her team found that:

•  White women slept the most, an average of six hours and 42 minutes a night, compared to the seven hours they thought they had slept.

•  White women took the shortest time to fall asleep, 13 minutes; stayed in bed the longest, eight hours; and slept the most efficiently.

•  Black men slept only five hours and six minutes a night, compared to only six hours they said they slept on weeknights.

•  Black men had the hardest time falling asleep, 36 minutes; spent the least time in bed, seven hours; and they had less sleep efficiency.

•  White men and black women slept about the same as their gender counterparts.

•  Someone making $16,000 a year or less takes 28 minutes longer to fall asleep than someone who earns over $100,000, and gets 15 minutes less sleep.

Fewer worries or more control?

Lauderdale says the gender and racial differences help up even when she considered income, employment and other factors. But lower income was closely linked to how long it took to get to sleep and lower sleep efficiency.

"People who make more money may have fewer worries, or they may have more control over their sleep environment," Lauderdale says. "There were psychological factors like worry which kept people from sleeping. People who earn less might also have less quiet and comfortable bedrooms, or other health problems that complicate sleep."

Findings from Lauderdale's project appear in a recent American Journal of Epidemiology. In an editorial in the same journal, sleep expert Dr. Stuart F. Quan from the University of Arizona says the findings indicate African Americans may suffer from sleep deprivation, although he warned the results may not apply to all middle-aged blacks and whites.

And the problem of sleeplessness may be getting worse as 21st century life becomes more hectic. A century ago, people claimed to get an average of nine hours a night, but by 1960, the norm had dropped to eight hours. Nowadays, most people say they get between six and a half and seven hours, Lauderdale says.

"Many people believe that it's testimony to the active and important lives they lead not to overestimate their sleep," she says. "I try to get at least seven hours a night. I can't function the next day without it."

Warning signs

Quan, Lauderdale and other sleep experts recommend you get at least seven hours of sleep a night. Lauderdale concedes, however, that a century ago, people claimed to have slept nine hours a night, compared to the six-and-a-half hours people today say they sleep.

They warn if you have trouble sleeping, you may have:

•  a higher rate of vehicle accidents;

•  a higher risk for diabetes, overeating and high blood pressure;

•  an inability to concentrate;

•  trouble learning;

•  decreased attention to detail.

10 tips on getting a good night's sleep

If you're having trouble getting a good night's sleep, follow these tips from the National Sleep Foundation: 

•  Maintain a regular bed and wake time schedule including weekends;

•  Establish a regular, relaxing bedtime routine such as soaking in a hot bath or hot tub and then reading a book or listening to soothing music;

•  Create a sleep-conducive environment that is dark, quiet, comfortable and cool;

•  Sleep on a comfortable mattress and pillows;

•  Use your bedroom only for sleep and sex;

•  Finish eating at least 2-3 hours before your regular bedtime;

•  Exercise regularly, but complete your workout at least three hours before bedtime;

•  Avoid the stimulant caffeine in coffee, tea, soft drinks and chocolate close to bedtime;

•  Avoid nicotine, another stimulant, close to bedtime;

•  Avoid alcohol, which is not a sedative, close to bedtime.