So says a new study in the May 14 issue of the Journal of the American Medical Association.
The activity can be modest, the researchers say, such as walking about a mile a day.
While other studies have also found that those who boost their physical activity reduce their heart disease risk and live longer, most of the research focused on middle-age people or men only, says study co-author Jane A. Cauley, a professor of epidemiology at the University of Pittsburgh.
The study looked at women aged 65 and older. It is one of the few, Cauley says, to examine changes in activity levels and how they affect older women. And the findings, she adds, contradict those in a study published in 1996 that found no effect on mortality among older Swedish women who took up exercise late in life.
Cauley and her colleagues evaluated more than 9,500 women at four research centers in Baltimore, Minneapolis, Monongahela Valley, Pa., and Portland, Ore. In the first evaluation, conducted between 1986 and 1988, the women were asked whether they were active and, if so, what they did. They were surveyed again during a second evaluation conducted from 1992 to 1994.
Those who increased their physical activity from the first evaluation to the second had a 48 percent lower death risk, compared with those women who continued to be sedentary. The women who got active also reduced their heart disease risk by 36 percent, and their cancer risk by 51 percent, according to the study.
The risks declined even after the researchers controlled for smoking, being overweight or having other diseases.
The median amount of exercise by the active group was about 8 miles a week -- or about a mile a day, Cauley says. "We're not talking about a marathon here," she says, "but primarily walking."
The increase in physical activity extends life spans, the researchers speculate, in several ways, including improving cardiovascular fitness and decreasing the risk of falls and the resulting fractures.
The message is clear, Cauley says. "It's never too late. Get moving."
While the benefits of increased activity waned a bit in the women over age 75, Cauley says, "I wouldn't put too much emphasis on that." That finding might not hold true in future studies, she says.
Dr. Ralph Paffenbarger Jr., professor emeritus of epidemiology at Stanford University School of Medicine and a pioneer in exercise studies, calls the new research "well done, nicely analyzed."
In a future study, he suggests the researchers examine the intensity of exercise among older people to see if they're doing enough.
"A lot of people that age think they are active [enough]," Paffenbarger says. They go to the mall and window shop and count it as exercise, he says. While he doesn't want to discourage that, he says many people may not be as active as they think.
Paffenbarger suggests older people looking to become more active invest in a pedometer to keep track of their steps. If an older person has a doctor's OK and is fit enough, he or she should aim to get in 6,000 steps a day, he says, adding, "That's about two-and-a-half miles."