TUESDAY, Dec. 11 (HealthDay News) -- A new study suggests that physically active people are likely to live several years longer than inactive people.

The findings don't say anything about whether those extra years are good ones, and the limits of the research don't prove that activity may guarantee longer life spans.

Still, the Canadian study adds more evidence that being active pays dividends in the long run.

The biggest effect came in black women. Those who reported getting at least two and a half hours of moderate activity a week were anticipated to live nearly six extra years. And white men who were active at age 20 were expected to live an extra two and a half years compared to their couch-potato counterparts. But Hispanics, for reasons that aren't clear, didn't get any gain from being more active.

Study author Ian Janssen, an associate professor who studies physical activity at Queen's University in Ontario, said the findings offer evidence that could convince the inactive to get up and start moving.

For example, "one of the reasons [people] tell you that they don't engage in physical activity is that it takes up so much of their time," Janssen said. "We were able to show that if black women engage in an hour of vigorous activity like jogging or swimming, that would extend their lives by 11 hours" -- or 11 hours for every hour spent exercising, he added.

It's no secret that activity and exercise are good for you since they reduce the risk of certain types of disease. It has been less clear what it does to life spans, especially in regard to people of different ages and ethnicities.

In the new study, researchers examined American health statistics from 1990 to 2006, including death rates and surveys about physical activity, and extrapolated them. They reported their findings online Dec. 11 in the American Journal of Preventive Medicine.

The study findings are a bit tricky to understand since they examine only the possible effects of physical activity at one point in a person's life, not throughout their lives.

For example, the study found that white women who were physically active at age 20 were expected to live three years longer than others. But that's based only on reports of how active they were at age 20 -- it's not clear whether they had to remain active over the rest of their lives to get those extra years.

As for older people, the study estimates that white men and women get a lifespan boost of 1.2 and 1.6 years, respectively, if they're active at age 80.

Hispanics appeared to gain nothing in terms of life span from physical activity, although that could be because the surveys weren't properly designed to ask questions appropriate to their culture, Janssen said.

The findings also are limited because it's possible that something other than activity -- such as a healthful diet -- boosted life spans in those who lived longer. The researchers did try to account for that, however.

Dr. Mark Wahlqvist, a visiting professor at Taiwan's National Health Research Institutes who studies physical activity, said a wider Taiwanese study released last year showed that as little as 15 minutes of activity a day can make a difference in terms of longer life span.

But will those extra years be good ones? Wahlqvist thinks so. "It is very likely that they will be ones with better social, mental and physical health," he said.

More information

For more about exercise, try the U.S. National Library of Medicine.