Think you do just fine on five or six hours of shut-eye? Chances are, you are among the many millions who unwittingly shortchange themselves on sleep.

　　Research shows that most people require seven or eight hours of sleep to function optimally. Failing to get enough sleep night after night can compromise your health and may even shorten your life. From infancy to old age, the effects of inadequate sleep can profoundly affect memory, learning, creativity, productivity and emotional stability, as well as your physical health.

　　According to sleep specialists at the University of Pittsburgh School of Medicine and Western Psychiatric Institute and Clinic, among others, a number of bodily systems are negatively affected by inadequate sleep: the heart, lungs and kidneys; appetite, metabolism and weight control; immune function and disease resistance; sensitivity to pain; reaction time; mood; and brain function.

　　Poor sleep is also a risk factor for depression and substance abuse, especially among people with post-traumatic stress disorder, according to Anne Germain, associate professor of psychiatry at the University of Pittsburgh. People with PTSD tend to relive their trauma when they try to sleep, which keeps their brains in a heightened state of alertness.

　　Dr. Germain is studying what happens in the brains of sleeping veterans with PTSD in hopes of developing more effective treatments for them and for people with lesser degrees of stress that interfere with a good night’s sleep.

　　The elderly are especially vulnerable. Timothy H. Monk, who directs the Human Chronobiology Research Program at Western Psychiatric, heads a five-year federally funded study of circadian rhythms, sleep strength, stress reactivity, brain function and genetics among the elderly. “The circadian signal isn’t as strong as people get older,” he said.

　　He is finding that many are helped by standard behavioral treatments for insomnia, like maintaining a regular sleep schedule, avoiding late-in-day naps and caffeine, and reducing distractions from light, noise and pets.

　　It should come as no surprise that myriad bodily systems can be harmed by chronically shortened nights. “Sleep affects almost every tissue in our bodies,” said Dr. Michael J. Twery, a sleep specialist at the National Institutes of Health.

　　Several studies have linked insufficient sleep to weight gain. Not only do night owls with shortchanged sleep have more time to eat, drink and snack, but levels of the hormone leptin, which tells the brain enough food has been consumed, are lower in the sleep-deprived while levels of ghrelin, which stimulates appetite, are higher.

　　In addition, metabolism slows when one’s circadian rhythm and sleep are disrupted; if not counteracted by increased exercise or reduced caloric intake, this slowdown could add up to 10 extra pounds in a year.

　　The body’s ability to process glucose is also adversely affected, which may ultimately result in Type 2 diabetes. In one study, healthy young men prevented from sleeping more than four hours a night for six nights in a row ended up with insulin and blood sugar levels like those of people deemed prediabetic. The risks of cardiovascular diseases and stroke are higher in people who sleep less than six hours a night. Even a single night of inadequate sleep can cause daylong elevations in blood pressure in people with hypertension. Inadequate sleep is also associated with calcification of coronary arteries and raised levels of inflammatory factors linked to heart disease. (In terms of cardiovascular disease, sleeping too much may also be risky. Higher rates of heart disease have been found among women who sleep more than nine hours nightly.)