When Paul Harris stays out late on a gig, he usually finds himself "in a fog" the next day. After getting only four hours' sleep, the 43-year-old musician and social activist says his singing voice and creativity suffer.
"I'm not as sharp," he says, sipping espresso diluted with decaf in a Charles Village coffee shop. "My body isn't running the way it should be."
Harris has plenty of company. While many of us have trouble getting a good night's sleep, many more scrimp on shut-eye because of work schedules, or simply by choice. American adults sleep less than seven hours a night on average, surveys show, and a third limit shut-eye to less than six hours to cram in more work or play.
Although some people do fine with less sleep, eight hours is still considered the norm - and there's a price to be paid for not getting it. Recent research indicates that chronic undersleeping does more than undermine productivity or make people more irritable and prone to dozing off. It also increases the risk of accidents and may contribute to serious, long-term problems such as obesity, diabetes and heart disease.
"Ours is a sleep-deprived society," says Dr. Steven M. Scharf, medical director of the University of Maryland Sleep Disorders Center. "We know that sleep is essential to life. Deprive rats of sleep, and they die."
Up to 60 percent of Americans report at least occasional sleep problems, according to the National Sleep Foundation. About 10 percent of adults suffer from chronic insomnia, which means they can't get to sleep, or they can't stay asleep through the night. About 6 percent have obstructive sleep apnea, in which the airways collapse repeatedly and disrupt normal slumber.
Willingly deprived or not, those who don't get enough sleep may be undermining their health, researchers say.
A national study published this year tracking 71,617 nurses found that women who got five hours of sleep or less nightly over a decade had a 39 percent greater risk of heart attack than those who managed eight hours.
Oddly, nurses who got nine hours or more also had more heart attacks than the eight-hour group. Dr. David White of Harvard Medical School, one of the study's authors, called that finding puzzling.
"There's not an obvious answer, unless there's some subtle sleep disorder we can't think of that's making them spend nine or 10 hours in bed," he said.
The nurses' study was the largest to date linking sleep deprivation with heart disease. Other short-term lab studies may suggest why it happens.
Scientists at the University of Chicago have found that building up a sleep "debt" over a matter of days can impair metabolism and disrupt hormone levels. After restricting 11 healthy young adults to four hours' sleep for six nights, researchers found their ability to process glucose (sugar) in the blood had declined - in some cases to the level of diabetics.
The sleep-deprived subjects also showed increased levels of the stress hormone cortisol, which were typical of much older people.
Cortisol is linked to problems that include insulin resistance and memory impairment. So researchers concluded that sleep loss may increase the severity of such age-related chronic health problems as obesity, diabetes and hypertension.
The notion that lack of sleep disturbs the body's chemistry does not surprise sleep specialists, who have concluded that sleep is much more than the absence of being awake.
For example, researchers who scanned sleepers' brains found that the areas involved in learning new tasks remain active in slumber, suggesting that sleep plays a role in storing information for future retrieval.
Many believe sleep helps restore biological processes that are degraded during the day. In deep sleep, for instance, the pituitary gland releases a growth hormone, which helps build bone and muscle tissue. Growth hormone deficiencies, on the other hand, can lead to loss of energy and muscle, and to obesity, research shows.
University of Chicago researchers found that as people age, the proportion of time they spend in deep sleep declines - from 20 percent for men under age 25 to less than 5 percent in men age 35 and over. Not surprisingly, the production of growth hormone is 75 percent lower in the 35-and-over group.
Severe sleep "debts" also tend to alter people's lifestyle in unhealthy ways.
"Basically healthy adults who are acutely sleep-restricted tend to eat more, and what they eat more of tends to be carbohydrates and high in fat," says Dr. Carl E. Hunt, director of the National Center on Sleep Disorders Research in Washington.
Few people, though, are aware of how short-changing sleep can affect their ability to function.
One study published this year found that after two weeks of four-hour sleep, a group of healthy young adults performed as poorly on tests of alertness, memory and mental agility as those who had gone without any sleep for two nights. Nor did they seem aware of their gradually deteriorating performance.