Even 15 minutes a day of brisk walking, cycling or swimming could help older adults live longer, according to a review of past research that found any physical activity is better than none.

For people over age 60, meeting current U.S. guidelines for moderate-to-vigorous exercise was linked to a 28 percent lower risk of dying over about 10 years, compared to being completely sedentary. But even lower levels of exercise were tied to a 22 percent reduction in mortality risk.

"When our older patients cannot do 150 minutes of moderate-intensity physical activity a week because of chronic diseases, we (the 2008 guidelines) recommend them to be as physically active as their abilities and conditions allow," said lead author Dr. David Hupin of the department of clinical and exercise physiology, University Hospital of Saint-Etienne, France, by email.

But, Hupin's team writes in the British Journal of Sports Medicine, the 150-minutes per week of moderate-to-vigorous exercise suggested in the 2008 Physical Activity Guidelines for Americans could be too much for some older adults, discouraging them from exercising. The authors point out that more than 60 percent of older adults don't meet that requirement.

For the new study, Hupin's team looked at whether less exercise could still be beneficial. They analyzed data from past studies covering a total of 122,417 men and women between the ages of 60 and 101 in the U.S., Taiwan and Australia.

The studies evaluated participants' physical activity levels and their risk of dying from any cause over about 10 years. Theyalso factored in participants' self-reported health status, physical or mental illnesses, weight, cholesterol and other details.

Hupin's team standardized participants' exercise amount and intensity into units known as Metabolic Equivalent of Task, or METs, representing the amount of energy expended per minute in a specific activity. Resting expends 1 MET, moderate activity like walking uses 3 to 5.9 METs and vigorous exercise like running uses more than 6 METs.

A weekly exercise "dose" was low if it totaled 1 to 499 METs, moderate at 500 to 999 METs and high if it was more than 1,000 METs.

The mortality rate was 22 percent lower among people in the low METs category than among those who did no exercise at all beyond the activities of daily living.

For people in the moderate METs category - which is equivalent to the recommended 150 minutes per week of moderate-to-vigorous exercise - there were 28 percent fewer deaths compared to those with no exercise.

People who expended at least 1,000 METs per week had a 35 percent lower mortality rate.

The link between exercise and mortality risk was especially strong for cardiovascular disease and less so for cancer, the researchers note.

Older women showed an even greater benefit from exercise than men, with their mortality risk decreasing by 32 percent compared to men's 14 percent in the low-METs category. One reason could be that women underestimated their exercise level and men overestimated theirs, the authors write.

The researchers recommend 15 minutes per day of exercise based on these results, but Hupin said adults who couldn't even meet that goal would benefit by merely moving around more on a consistent basis.

"Scientific evidence is now emerging to show that there may be health benefits from light physical activity and from replacing sedentary activities with light intensity activities, when the dose of (moderate-to-vigorous physical activity) is held constant," Hupin said. "They must become less sedentary: cooking or working at a standing desk, rather than sitting.

"Age is not an excuse to do no exercise," he said.

Thomas Buford, who directs the Health Promotion Center at the University of Florida in Gainesville, said that while the study offered great examples of exercise, such as walking briskly, bicycling and swimming or gymnastics, he agreed that even increasing exercise in small bouts would help.

"For each individual, they would have to be tailored depending on their physical abilities," Buford said by email.