As many as half of Americans experience some sleep problems during the course of a year and one-quarter have chronic difficulties sleeping that may be harming their health.
Good quality sleep ''should be considered an essential component of a healthy lifestyle, as much as exercise and nutrition,'' said researcher Phyllis Zee of Northwestern University Feinberg School of Medicine in Chicago.
Zee, who coauthored an editorial commenting on several studies in this month's issue of the Archives of Internal Medicine examining the repercussions of sleep disorders, said scientists have yet to fully understand the mechanisms by which lack of sleep hurts the body.
''We do know that people who get less than seven hours of sleep a day are at higher risk of metabolic disorders and cardiovascular disease,'' she said in a telephone interview yesterday.
Lack of sleep appears to increase levels of cytokines, which are molecules released by the immune system that control the body's immune response. The resulting inflammation may be responsible for a host of ills from heart disease to diabetes to neurological diseases.
It may be that sleep refreshes the immune system and resets the body's autonomic nervous system that controls bodily functions, researchers said.
''What is it about sleep and sleep duration that ... effects changes in metabolism, changes in cardiovascular function? We just don't know,'' Zee said.
SLEEP AND DEPRESSION In one study in the journal, sleep studies performed over a four-year period on 1,408 middle-aged adults found those with sleep apnea -- where the airway becomes blocked repeatedly, interrupting sleep -- were twice as likely to develop depression.
''The study is the first the show that sleep apnea is a risk factor for depression,'' Zee said, suggesting that physicians treating people for depression ought to ask about sleep habits and try to address them.
Other studies in the journal found sleep deficits affected aspects of the immune system, but Zee said this type of research was just beginning.
Another study found diabetic men who tended to have short or poor-quality sleep had less control of their blood-sugar levels, and suggested one way to improve the health of such patients might be to recommend more sleep.
''The growing tendency to burn the candle at both ends may be a significant contributor to the current epidemic of diabetes,'' said Kristen Knutson of the University of Chicago, the author of the study on diabetic men.
The pain from various health problems can contribute to poor sleep, which in turn can worsen the illnesses, Zee noted.
Reuters LL GC0929