Even as little as 75 minutes a week of physical activity can extend your life by nearly two years, according to U.S. researchers who found some benefits regardless of body weight.

The study by Steven Moore of the U.S. National Cancer Institute and his co-authors also suggests that regular activity would boost life expectancy even more.

The researchers pooled data on 650,000 men and women aged 40 and older in Sweden and the U.S. who reported their activity levels.

The findings show that 75 minutes a week — or just over 10 minutes a day — was associated with 1.8 years of added life expectancy, compared to getting no leisure-time activity.

As well, brisk walking for 450 minutes a week, just over an hour a day, was associated with living 4.5 years longer.

The researchers in the study in PLOS Medicine hope the findings convince sedentary people that even a modest physical activity program can boost health. (Nikki Carlson/Havre Daily News/Associated Press)

"More leisure-time physical activity was associated with longer life expectancy across a range of activity levels and body mass index groups," they said in the November issue of the journal PLOS Medicine, published by the Public Library of Science.

Investigators also considered weight categories:

• Being active and at a normal weight — the best-case scenario — were associated with a gain of 7.2 years of life, compared with being inactive and in the highest obese category.
• A normal-weight person who is inactive could face a loss of 4.7 years of life.

"This finding may help convince currently inactive persons that a modest physical activity program is 'worth it' for healthy benefits, even if it may not result in weight control."

Long-term cigarette smoking reduces life expectancy by about 10 years, notes the study, which was funded by the U.S. National Cancer Institute and U.S. National Institutes of Health.

Intensity rule of thumb

Between 2007 and 2009, only 15 per cent of adults were getting the recommended 150 minutes of moderate to vigorous physical activity to gain health benefits, according to Statistics Canada's Health Measures survey.

"As a good rule of thumb, if you're taking time and you have to think about your breathing and you feel that you're warm and sweaty afterwards, that's the type of activity we're looking at to get these health benefits," said Dr. Mark Tarnopolsky of the pediatrics department at McMaster University in Hamilton, where he studies how exercise helps metabolism such as repairing age-related damage.

What this study and others suggest is that it's the first 30 minutes of vigorous activity that gives the majority of benefits, Tarnopolsky added.

Lack of motivation is a common barrier to getting physical activity, says Tanya Berry. (CBC)

A journal editorial cautioned that participants self-reported their heights and weights and leisure-time physical activity, which may have been overestimated.

Other factors also could have influenced the findings in the observational study, although the researchers did take variables such as use of tobacco and alcohol into account.

Overcoming barriers to physical activity

"These findings reinforce the public health message that both a physically active lifestyle and a normal body weight are important for increasing longevity," the editors wrote.

The challenge is getting people to act on the knowledge that physical activity is important for health, said Spencer Moore, an assistant professor in the school of kinesiology and health studies at Queen’s University in Kingston, Ont.

"In our work, we focus on the importance of having supportive social (e.g., active peers) and built (e.g., available parks, walkable neighbourhoods) environments," Moore said in an email.

"Individuals make the decision to be physically active or not. Having supportive environments around us, however, help to make the healthy choice the easy choice."

Tanya Berry, Canada Research Chair in physical activity promotion at the University of Alberta in Edmonton, studies barriers to physical activity.

Time is the top reason cited for not exercising, said Berry.

In Toronto, Melissa Perugini, 20, said she gets no exercise. "Too busy with school and work. No time," she said.

But when people fill out diaries on how they spend their day, Berry adds, most would be able to carve out 35 or 40 minutes a day to at least go for a walk.

"When you're thinking about leisure-time physical activities, where are your priorities?" Berry said. "For a lot of people, physical activity isn't something they enjoy and it's not something that's a priority for them, so motivation becomes a big, big issue."

The immediate increases in energy levels and time spent together being active as a family can be motivating factors.

With files from CBC's Pauline Dakin and Kelly Crowe