People who don't exercise can extend their life expectancy by getting as little as 15 minutes of physical activity a day, a study by Taiwanese researchers suggests.

Currently, physical activity guidelines from authorities such as the World Health Organization recommend that people move 30 minutes a day, five days a week. But couch potatoes often say that  time constraints and uncertainty about how much exercise  they need to help their health prevent them from meeting the goal, researchers say.

Now investigators have studied more than 400,000 men and women in Taiwan who were asked how much exercise they did in the previous month. Participants were followed for an average of eight years. The findings suggest it may take only half that recommended time — 15 minutes a day — to gain health benefits.

"Fifteen minutes a day or 90 minutes a week of moderate-intensity exercise might be of benefit, even for individuals at risk of cardiovascular disease," Dr. Chi-Pang Wen, of the National Health Research Institutes in Taiwan, and co-authors concluded in Tuesday's online issue of the medical journal The Lancet.

Moderate-intensity exercise included brisk walking.

The researchers estimate that if people in Taiwan did 15 minutes of exercise on average then one in six deaths from all causes could be postponed — a similar level to that of tobacco-control programs.

Fitting in exercise

"The knowledge that as little as 15 minutes per day of exercise on most days of the week can substantially reduce an individual’s risk of dying could encourage many more individuals to incorporate a small amount of physical activity into their busy lives," Anil Nigam and Martin Juneau of the Montreal Heart Institute and University of Montreal said in a journal commentary published with the study.

"Governments and health professionals both have major roles to play to spread this good news story and convince people of the importance of being at least minimally active."

In the study, those who were inactive had a 1.17 times higher risk of death compared with those in the low-volume activity group, the researchers found.

Compared with those in the inactive group, at age 30, life expectancy for those in the low-volume group was 2.55 years longer for men and 3.10 years longer for women, the investigators said.

For those who met the recommended amount of exercise, life expectancy was 4.21 years longer for men and 3.67 years longer for women.

"The more exercise you do the better, but every step counts," said Dr. Lennert Veerman, from the School of Population Health at the University of Queensland in Brisbane.

Once someone starts doing 15 minutes of exercise a day regularly, they might be more likely to increase the time they spend exercising per day, the study's authors said.

Weekend warrior warning

The new results also suggested that doing vigorous-intensity exercise such as jogging once or twice a week — so-called "weekend warriors" — could give similar health benefits as doing four hours a week of moderate-intensity exercise, the Taiwanese team noted.

But they cautioned that weekend warriors should not be encouraged because of the potential for increased injury and cardiovascular risks.

The results applied to the Taiwanese population studied — who were mainly of above average income or socioeconomic status — and might not apply to all east Asians, the authors said.

The answers were self-reported, and the observational study can't establish a cause-and-effect relationship, the journal commentary noted.

Still, compared with the 60 to 90 minutes of moderate-to-vigorous exercise recommended daily for adults in Canada, the 15-minute approach was welcomed by some in Toronto.

"When they say it is only 15 minutes, it's kind of nice that you can put that in your daily schedule," said Paul Diprofio.

"Fifteen minutes would be great, especially if I could do it in my home gym instead of having to go out. It would save a lot of time," said Jennifer Wilson.

The research was funded by the Taiwan Department of Health Clinical Trial and Research Centre of Excellence and the National Health Research Institutes.

With files from CBC's Philip Lee-Shanok and Australian Broadcasting Corp.