The mega-study is part of a growing body of research showing that some physical activity provides health benefits - even when levels fall below the recommended federal guidelines of 150 minutes of moderate-intensity physical activity a week.
For the first time since 1998, the American College of Sports Medicine updated its exercise guidelines in June, including information on how little exercise is needed to achieve health benefits.
"The biggest health benefits we saw were for those who went from doing nothing to those doing something small," says Jacob Sattelmair, author of the new AHA study. "Even a little bit of activity makes a significant difference."
A little bit means 10 to 15 minutes a day. Sattelmair says the new findings are the first to make quantitative assessments of the amount of physical activity a person needs to reduce risk.
"Early studies broke people into groups such as active and sedentary," he says. "More recent studies have begun to assess the actual amount of physical activity people are getting and how that relates to the risk of heart disease."
The ACSM guidelines also say as little as half - about 75 minutes a week - can be helpful, while stressing more is needed to maintain a healthy weight and achieve maximum benefits.
"It's very clear that a little bit of exercise makes a big difference," says Carol Ewing Garber, author of the ACSM's new guidelines and assistant professor of movement at Columbia University. "
The recommendation to get 150 minutes a week of moderate-intensity exercise is still one of the goals, but the message needs to be heard that doing less is also helpful."
The findings published Monday in Circulation do not list a percentage for the magnitude of lower heart disease risk for those who meet half the guideline because of the methodology used, Sattelmair says.
•People who do 150 minutes of moderate intensity (or 75 minutes of high intensity) have a 14% lower risk of heart disease compared with sedentary people.
"That's not as robust as people might expect but it's still significant," Sattelmair adds.
•There's a progressive reduction of risk. If you do twice the guidelines (300 minutes), you lower your risk 20%. If you do 750 minutes, risk drops to 25%.
"It's feasible to rack up two hours of movement a day," Sattelmair says. "That's clearly what we're designed to do."
•Women got more benefit from exercise. "We did not have a good explanation for why this is," says Sattelmair, adding that more research is necessary to explore the issue.
While not part of the new findings, breaking up the day with exercise is also key to establishing good health, Sattelmair says. Several studies have shown that meeting the guidelines of 150 minutes a week is not enough if you spend the rest of your time on the sofa or sitting at a computer.
Garber says research shows that long durations of physical inactivity during the day raise your risk of developing heart disease, diabetes, cancer and obesity.
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