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Phys Ed Gretchen Reynolds on the science of fitness.

Offering hope and encouragement to the many adults who have somehow neglected to exercise for the past few decades, a new study suggests that becoming physically active in middle age, even if someone has been sedentary for years, substantially reduces the likelihood that he or she will become seriously ill or physically disabled in retirement.

The new study joins a growing body of research examining successful aging, a topic of considerable scientific interest, as the populations of the United States and Europe grow older, and so do many scientists. When the term is used in research, successful aging means more than simply remaining alive, although that, obviously, is the baseline requirement. Successful aging involves minimal debility past the age of 65 or so, with little or no serious chronic disease diagnoses, depression, cognitive decline or physical infirmities that would prevent someone from living independently.

Previous epidemiological studies have found that several, unsurprising factors contribute to successful aging. Not smoking is one, as is moderate alcohol consumption, and so, unfairly or not, is having money. People with greater economic resources tend to develop fewer health problems later in life than people who are not well-off.

But being physically active during adulthood is particularly important. In one large-scale study published last fall that looked at more than 12,000 Australian men aged between 65 and 83, those who engaged in about 30 minutes of exercise five or so times per week were much healthier and less likely to be dead 11 years after the start of the study than those who were sedentary, even when the researchers adjusted for smoking habits, education, body mass index and other variables.

Whether exercise habits need to have been established and maintained throughout adulthood, however, in order to affect aging has been less clear. If someone has slacked off on his or her exercise resolutions during young adulthood and early middle-age, in other words, is it too late to start exercising and still have a meaningful impact on health and longevity in later life?

To address that issue, researchers with the Physical Activity Research Group at University College London and other institutions turned recently to the large trove of data contained in the ongoing English Longitudinal Study of Aging, which has tracked the health habits of tens of thousands of British citizens for decades, checking in with participants multiple times and asking them how they currently eat, exercise, feel and generally live.

For the study, appearing in the February issue of the British Journal of Sports Medicine, scientists isolated responses from 3,454 healthy, disease-free British men and women aged between 55 and 73 who, upon joining the original study of aging, had provided clear details about their exercise habits, as well as their health, and who then had repeated that information after an additional eight years.

The researchers stratified the chosen respondents into those who were physically active or not at the study’s start, using the extremely generous definition of one hour per week of moderate or vigorous activity to qualify someone as active. Formal exercise was not required. An hour per week of “gardening, cleaning the car, walking at a moderate pace, or dancing” counted, said Mark Hamer, a researcher at University College London who led the study.

The scientists then re-sorted the respondents after the eight-year follow-up, marking them as having remained active, become active, remained inactive or become inactive as they moved into and through middle-age. They also quantified each respondent’s health throughout those years, based on diagnosed diabetes, heart disease, dementia or other serious conditions. And the scientists directly contacted their respondents, asking each to complete objective tests of memory and thinking, and a few to wear an activity monitor for a week, to determine whether self-reported levels of physical activity matched actual levels of physical activity. (They did.)

In the eight years between the study’s start and end, the data showed, those respondents who had been and remained physically active aged most successfully, with the lowest incidence of major chronic diseases, memory loss and physical disability. But those people who became active in middle-age after having been sedentary in prior years, about 9 percent of the total, aged almost as successfully. These late-in-life exercisers had about a seven-fold reduction in their risk of becoming ill or infirm after eight years compared with those who became or remained sedentary, even when the researchers took into account smoking, wealth and other factors.

Those results reaffirm both other science and common sense. A noteworthy 2009 study of more than 2,000 middle-aged men, for instance, found that those who started to exercise after the age of 50 were far less likely to die during the next 35 years than those who were and remained sedentary. “The reduction in mortality associated with increased physical activity was similar to that associated with smoking cessation,” the researchers concluded.

But in this study, the volunteers did not merely live longer; they lived better than those who were not active, making the message inarguable for those of us in mid-life. “Build activity into your daily life,” Dr. Hamer said. Or, in concrete terms, if you don’t already, dance, wash your car and, if your talents allow (mine don’t), combine the two.