JANE E. BRODY ESSAY

Regular exercise is the only wellestablished fountain of youth, and it’s free. What, I’d like to know, will persuade the millions of people who remain sedentary to get up and give their bodies the workout they deserve? My hope is that every new testimonial to the value of exercise will win a few more converts until everyone is doing it.

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, North Carolina, pointed to “the power of higher levels of physical activity to aid in the prevention of latelife 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.”

Taking the benefits of exercise one system at a time, here is what recent studies have shown, including several published in The Archives of Internal Medicine in December. Most early studies demonstrating the benefits of exercise were done with men. Now a raft of recent studies has shown that active women reap comparable rewards.

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.

Osteoporosis and fragility. Weightbearing aerobic activities like brisk walking and weight training to increase muscle strength can reduce or even reverse bone loss. In one of the new studies, German researchers who randomly assigned women 65 and older to either an 18-month exercise regimen or a wellness program demonstrated that exercise significantly increased bone density and reduced the risk of falls. And at any age, even in people over 100, weight training improves the size and quality of muscles .

Cardiovascular disease. Aerobic exercise has long been established as an invaluable protector of the heart and blood vessels.

Though early studies were conducted only among men, in a 2002 study published in The New England Journal of Medicine, Dr. JoAnn E. Manson and colleagues 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.

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 prediabetic 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. A 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.

One study conducted in Australia and published in September 2008 in The Journal of the American Medical Association randomly assigned 170 volunteers who reported memory problems to a six-month program of physical activity or health education. A year and a half later, the exercise group showed “a modest improvement in cognition.”