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For people who exercise but fret that they really should be working out more, new studies may be soothing. The amount of exercise needed to improve health and longevity, this new science shows, is modest, and more is not necessarily better.

Phys Ed Gretchen Reynolds on the science of fitness.

That is the message of the newest and perhaps most compelling of the studies, which was presented on Saturday at the annual meeting of the American College of Sports Medicine in San Francisco. For it, researchers at the University of South Carolina Arnold School of Public Health and other institutions combed through the health records of 52,656 American adults who’d undergone physicals between 1971 and 2002 as part of the Aerobics Center Longitudinal Study at the Cooper Institute in Dallas. Each participant completed physical testing and activity questionnaires and returned for at least one follow-up visit.

The researchers found that about 27 percent of the participants reported regularly running, although in wildly varying amounts and paces.

The scientists then checked death reports.

Over the course of the study, 2,984 of the participants died. But the incidence was much lower among the group that ran. Those participants had, on average, a 19 percent lower risk of dying from any cause than non-runners.

Notably, in closely parsing the participants’ self-reported activities, the researchers found that running in moderation provided the most benefits. Those who ran 1 to 20 miles per week at an average pace of about 10 or 11 minutes per mile — in other words, jogging — reduced their risk of dying during the study more effectively than those who didn’t run, those (admittedly few) who ran more than 20 miles a week, and those who typically ran at a pace swifter than seven miles an hour.

“These data certainly support the idea that more running is not needed to produce extra health and mortality benefits,” said Dr. Carl J. Lavie, medical director of cardiac rehabilitation and prevention at the Ochsner Medical Center in New Orleans and an author of the study. “If anything,” he continued, “it appears that less running is associated with the best protection from mortality risk. More is not better, and actually, more could be worse.”

His analysis echoes the results of another new examination of activity and mortality, in which Danish scientists used 27 years’ worth of data collected for the continuing Copenhagen City Heart Study. They reported that those Danes who spent one to two and a half hours per week jogging at a “slow or average pace” during the study period had longer life spans than their more sedentary peers and than those who ran at a faster pace.

This decidedly modest amount of exercise led to an increase of, on average, 6.2 years in the life span of male joggers and 5.6 years in women.

“We can say with certainty that regular jogging increases longevity,” Dr. Peter Schnorr, a cardiologist and an author of the study, said in presenting the findings at a clinical meeting organized last month by the European Association for Cardiovascular Prevention and Rehabilitation. “The good news is that you don’t actually need to do that much to reap the benefits.”

“The relationship appears much like alcohol intakes,” he continued. “Mortality is lower in people reporting moderate jogging than in non-joggers or those undertaking extreme levels of exercise.”

There’s further confirmation of that idea in the findings of a large study of exercise habits published last year in The Lancet, which showed that among a group of 416,175 Taiwanese adults, 92 minutes a week of moderate exercise, like walking, gentle jogging or cycling, increased life span by about three years and decreased the risk of mortality from any cause by about 14 percent.

In that study, those who embarked on more ambitious exercise programs did gain additional risk reduction, as seems only fair, but the benefits plateaued rapidly. For each further 15 minutes per day of moderate exercise that someone completed beyond the first 92, his or her mortality risk fell, but by only about another 4 percent.

Whether and at what point more exercise becomes counterproductive remains uncertain. “In general, it appears that exercise, like any therapy, results in a bell-shaped curve in terms of response and benefit,” says Dr. James H. O’Keefe, a cardiologist and lead author of a thought-provoking review article published on Monday in Mayo Clinic Proceedings that examines whether extreme amounts of vigorous exercise, particularly running, can harm the heart.

“To date, the data suggests that walking and light jogging are almost uniformly beneficial for health and do increase life span,” Dr. O’Keefe says. “But with more vigorous or prolonged exercise, the benefits can become questionable.

“I’m a fan of distance running,” he adds. “I run. But after about 45 to 60 minutes a day, you reach a point of diminishing returns, and at some point, you risk toxicity.”

His advice? The study by Dr. Lavie and his colleagues offers excellent guidelines for safe and effective exercise, Dr. O’Keefe says. “Twenty miles a week or less of jogging at a 10- or 11-minute-mile pace can add years to your life span. That’s very good news.” Indeed it is — especially since that routine happens to replicate almost exactly my own weekly exercise regimen.

“I wouldn’t automatically discourage people from doing more if they really want to” and are not experiencing side effects, like extreme fatigue or repeated injuries, Dr. O’Keefe continued. “But the message from the latest data is that the sweet spot for exercise seems to come with less.”

Gretchen Reynolds is the author of “The First 20 Minutes: Surprising Science Reveals How We Can Exercise Better, Train Smarter, Live Longer” (Hudson Street Press, 2012).

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