Exercise lengthens life, even if you're overweight

CNN - Add this to the list of reasons why exercise is good for you: A new study says 150 minutes a week of moderate-intensity, leisure time exercise is associated with roughly 3.4 years added to a person's life.

Researchers from the National Cancer Institute, Harvard Medical School, and other organizations analyzed six different prospective cohort studies of more than 632,000 people ages 40 and older. The studies had a median follow-up period of 10 years, with roughly 82,000 reported deaths. Regular, moderate intensity exercise was associated with an increased life expectancy, even when the person exercising had an unhealthy Body Mass Index (BMI).

Dr. I-Min Lee, a professor of medicine at Harvard Medical School and the senior author of the study, says that not exercising but having a healthy weight was associated with 3.1 fewer years of life, compared to obese people who were active. Conversely, people who exercised 150 minutes a week and had a healthy BMI gained an extra 7.2 years of life.

While it's best to be at a healthy weight for your body, Lee thinks her team's analysis demonstrates that every bit of activity helps, regardless of a person's size.

"This shows if you emphasize physical activity, you still get the benefit," says Lee. "Overweight, obese, severely obese - if you are active, the results suggest that you ... have more of a benefit than someone who is not heavy but not active."

Lee and her team based their calculations on the World Health Organization's recommendation that adults should get at least 150 minutes of moderate to vigorous activity a week. They defined leisure time activity as any physical activity that wasn't a part of the participants' jobs, commute, or routine housework, such as organized sports, walking, bowling, gardening and hiking.

The analysis has its limitations, most notably that the studies it's based on used self-reported data to determine how much the participants exercised in their spare time and how much they weighed. Also, the studies did not take into account any activity that was done during the participants' jobs or housework.

Still, Lee says the data is a good reminder that it doesn't take a lot of time for people to be active and do something to help them live longer.