Want to Live Longer? Optimal Amount of Exercise Revealed
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Doing a few hours of exercise every week will probably help you live longer, but doing a whole lot more exercise doesn't provide much extra benefit, according to a new study on physical activity and longevity.

Still, doing as much as 10 times the recommended amount of exercise was not linked with an increased risk of dying during the study period. That's good news for marathon runners and triathletes who may have been concerned about the long-term health effects of such high levels of activity.

In the study, researchers analyzed information from more than 660,000 people ages 21 to 98 in the United States and Sweden who answered questions about how much time they spent doing physical activity, including walking, running, swimming and bicycling. (These questions were asked as part of earlier research conducted in the 1990s and 2000s.)

People who got some exercise, but not enough to meet the physical activity recommendations were still 20 percent less likely to die over a 14-year period than those who did not do any physical activity. (The recommendations say to do 150 minutes of moderate activity per week or 75 minutes of vigorous activity per week.)

People who engaged in the recommended level of physical activity saw even more benefit: They were 31 percent less likely to die during the study period, compared with those who did not engage in any physical activity.  [7 Common Exercise Errors and How to Fix Them]

But doing a lot more activity than that did not provide much added benefit. The maximum benefit was seen among people who engaged in three to five times the recommended levels of physical activity; they were 39 percent less likely to die over the study period than people who did no exercise. Engaging in more exercise than this was not linked with any additional benefit.

Although some earlier studies suggested that people who practice extreme endurance training have an increased risk of heart problems, the new study found no link between very high levels of physical activity (10 or more times the recommended level) and an increased risk of death.

"These findings are informative for individuals at both ends of the physical activity spectrum: They provide important evidence to inactive individuals by showing that modest amounts of activity provide substantial benefit for postponing mortality while reassuring very active individuals of no exercise-associated increase in mortality risk," the researchers, from the National Cancer Institute, wrote in the April 6 issue of the journal JAMA Internal Medicine.

In an editorial accompanying the study, Todd Manini, of the University of Florida's Department of Aging and Geriatric Research, pointed out that the people most likely to benefit from increasing the amount of exercise they do are those who do not currently do any.

"A lot of the mortality reductions were seen in people only one step away from doing no leisure-time physical activity," Manini said, referring to the group that did some physical activity, but not enough to meet the recommendations.

Doctors should target this group with exercise counseling, Manini said. "Physicians who seek out the segment of the population that performs no leisure-time physical activity could receive the most payback in their patient's health."

The new study relied on reports of physical activity at one point in time, and it's possible that people changed their levels of physical activity over the study period, the researchers said.

In addition, the study looked at the time spent engaged in physical activity, but did not focus on the intensity of that activity. That is, it did not directly compare those who engaged in moderate activity versus those who engaged in vigorous activity. But the study did find that people who met the recommended level of physical activity — either through moderate or vigorous activity levels — had a reduced risk of death.

In a separate study, also published today in JAMA Internal Medicine, researchers in Australia found that people who engaged in vigorous activity (such as jogging or aerobics) were 9 to 13 percent less likely to die over a six-year period than those who engaged in only moderate activity (such as gentle swimming or household chores).

"Our research indicates that even small amounts of vigorous activity could help reduce your risk of early death," study researcher Klaus Gebel, of James Cook University's Centre for Chronic Disease Prevention in Australia, said in a statement.

But people with medical conditions, older adults or those who have not previously engaged in vigorous activity should speak with their doctors before beginning an exercise program, Gebel said.

Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.