WASHINGTON: When it comes to living longer, fitness may trump fatness, US researchers said on Tuesday.

Men and women who were fit, as judged by a treadmill test, but were overweight or obese had a lower mortality risk than those of normal weight but low fitness levels, the study in the Journal of the American Medical Association showed.

Exercise expert Steven Blair of the University of South Carolina and colleagues tracked about 2,600 people age 60 and up, examining how physical fitness and body fat affected their death rates over 12 years.

Those in the lowest fifth in terms of fitness had a death rate four times higher than participants ranked in the top fifth for fitness. "Being fit provides protection against mortality in these men and women 60 and older, whether they're normal weight, overweight or obese," Blair said.

The findings are particularly relevant as people in the US and many other countries live increasingly sedentary lifestyles and obesity rates remain high. At the same time, the populations are aging in many nations.

"I believe we have an obesity epidemic. It's a bad sign. We should not ignore obesity," Blair said. "But what happens all too often is we focus nearly exclusively on obesity and forget the activity and fitness part." The researchers assessed the fitness of the participants using a treadmill test, seeing how long they could walk while the treadmill's incline increased. The study showed that even a modest effort to improve physical activity can provide health benefits, the researchers said. Those in the bottom fifth in terms of fitness were about twice as likely to die than those in the next fifth.