In a commentary on the new studies, published January 25 in The Archives of Internal Medicine, two geriatricians, Dr. Marco Pahor of the University of Florida and Dr. Jeff Williamson of Winston-Salem, N.C., pointed to "the power of higher levels of physical activity to aid in the prevention of late-life disability owing to either cognitive impairment or physical impairment, separately or together." "Physical inactivity," they wrote, "is one of the strongest predictors of unsuccessful aging for older adults and is perhaps the root cause of many unnecessary and premature admissions to long-term care." "...Higher quantities of physical activity have beneficial effects on numerous age-related conditions such as osteoarthritis, falls and hip fracture, cardiovascular disease, respiratory diseases, cancer, diabetes mellitus, osteoporosis, low fitness and obesity, and decreased functional capacity."

In another study of 13,535 nurses who were healthy when they joined the study in 1986, those who reported higher levels of activity in midlife were far more likely to still be healthy a decade or more later at age 70. The study found that physical activity increased the nurses' chances of remaining healthy regardless of body weight, although those who were both lean and active had "the highest odds of successful survival."

Here is what recent studies have shown, including several published in The Archives of Internal Medicine in December.

Cancer.  In a review last year of 52 studies of exercise and colon cancer, researchers at Washington University School of Medicine in St. Louis concluded that people who were most active were 21 percent less likely to develop the disease than those who were least active, possibly because activity helps to move waste more quickly through the bowel. The risk of breast cancer, too, is about 16 percent lower among physically active women, perhaps because exercise reduces tissue exposure to insulin-like growth factor, a known cancer promoter. Indirectly, exercise may protect postmenopausal women against cancers of the endometrium, pancreas, colon and esophagus, as well as breast cancer, by helping them keep their weight down.

Cardiovascular disease. Aerobic exercise has long been established as an invaluable protector of the heart and blood vessels. It increases the heart's ability to work hard, lowers blood pressure and raises blood levels of HDL-cholesterol, which acts as a cleansing agent in arteries. As a result, active individuals of all ages have lower rates of heart attacks and strokes. In a 2002 study published in The New England Journal of Medicine, researchers found that among 73,743 initially healthy women ages 50 to 79, walking briskly for 30 minutes a day five days a week, as well as more vigorous exercise, substantially reduced the risk of heart attacks and other cardiovascular events. In another study, women who walked at least one hour a day were 40 percent less likely to suffer a stroke than women who walked less than an hour a week.

Diabetes. Moderate activity has been shown to lower the risk of developing diabetes even in women of normal weight. A 16-year study of 68,907 initially healthy female nurses found that those who were sedentary had twice the risk of developing diabetes, and those who were both sedentary and obese had 16 times the risk when compared with normal-weight women who were active.  Another study that randomly assigned 3,234 pre-diabetic men and women to modest physical activity (at least 150 minutes a week) found exercise to be more effective than the drug Metformin at preventing full-blown diabetes.

Dementia. As the population continues to age, perhaps the greatest health benefit of regular physical activity will turn out to be its ability to prevent or delay the loss of cognitive functions. The new study of 3,485 healthy men and women older than 55 found that those who were physically active three or more times a week were least likely to become cognitively impaired.