THURSDAY, March 3 (HealthDay News) -- More than one-third of Americans routinely sleep fewer than seven hours a night, which affects their concentration and general health, new government research shows.

Insufficient sleep also impairs work performance and the ability to drive safely, found researchers for the U.S. Centers for Disease Control and Prevention (CDC), which published two sleep studies March 4 in its Morbidity and Mortality Weekly Report.

"Over the last 20 years there has been a decline in overall sleep duration in adults," said lead author of one report, Lela McKnight-Eily, a clinical psychologist and epidemiologist at the CDC's National Center for Chronic Disease Prevention.

Changing lifestyle habits, including longer workdays and late nights on the computer, have pared away much-needed sleep time, she noted. "Within our culture there seems to be a belief that sleep isn't a part of overall essential health," she said.

The National Sleep Foundation recommends that adults sleep for seven to nine hours a night to maintain good health.

But when McKnight-Eily's team studied the sleep habits of 74,571 adults in 12 states, 35.3 percent reported sleeping less than seven hours.

In addition, 48 percent reported snoring, 37.9 percent said they fell asleep at least once during the day the previous month and 4.7 percent admitted to falling asleep at the wheel at least once.

According to the U.S. Department of Transportation, drowsiness or nodding off while driving accounts for 1,550 deaths and 40,000 injuries a year.

Three percent of drivers in Illinois admitted to nodding off while driving the previous month, compared to 6.4 percent in Hawaii and Texas.

Hawaii also reported the highest number of people with poor sleep behaviors, the researchers noted.

For the other report, a group led by Anne Wheaton, a researcher in CDC's division of chronic disease prevention, looked at the impact of sleep deprivation on the ability to perform daily activities.

In that group, 37.1 percent reported getting less than seven hours sleep a night, and about one-quarter of these people said they had trouble concentrating. About 18 percent reported memory difficulties, and 8.6 percent said they were so sleepy during the day that it was hard to perform well at work.

People who slept less than seven hours were more likely to have all these problems, compared with people who got seven to nine hours of sleep a night, the researchers said. Increasing sleep time would likely improve everyday functioning, they added.

Chronic sleep loss also is associated with obesity, increased risk of death and other health problems, notes the CDC, which released these studies in conjunction with National Sleep Awareness Week, March 7 to 13.

For a good night's rest, people need to maintain a consistent sleep schedule and avoid stimulating activities like exercise close to bedtime, Wheaton said.

"The bedroom should be conducive to sleep. Not too hot, there is not too much light, not a lot of noise -- so it's just a comfortable environment," Wheaton said.

"Sometimes we just have to unplug," McKnight-Eily added. "Unplug the TV, unplug the radio, our BlackBerrys and computers."

Commenting on these reports, sleep specialist Dr. Shirin Shafazand said insufficient sleep "has an impact on how [people] perceive their quality of life, and their ability to concentrate, and their memory and learning skills."

Although all the benefits of sleep aren't known, studies have found it aids memory, learning and hormonal balance, which may be why lack of sleep is linked to obesity, added Shafazand, an assistant professor of medicine at the University of Miami Miller School of Medicine.

"It is clear that a lot of restorative activities are going on in the body during sleep," Shafazand said.

"We have to make a conscious effort to pay as much attention to sleep as people do to other healthy activities like exercise and eating right, because they are all linked together," she said.

More information

For more information on sleep, visit the National Sleep Foundation.