Regular physical activity extends life expectancy, even for people who are overweight, a large new study has found.
"Adding even low amounts of leisure time physical activity to one's daily routine — such as 75 minutes of walking per week — may increase longevity," researchers from the United States and Sweden said.
But for those who are obese and inactive, the news is all bad.
"A lack of leisure time physical activity when combined with obesity is associated with markedly diminished life expectancy," the authors of the study, published in PLOS Medicine, said.
The researchers used information on leisure time physical activities and body mass index from more than 650,000 people aged over 40 years in a combined analysis of six long term studies - one from Sweden and five from the US.
They found that even leisure time physical activity at a level equivalent to brisk walking for up to 75 minutes a week was associated with an average increase in life expectancy of 1.8 years, compared to those who did not exercise.
Leisure time physical activity at the level recommended by the World Health Organisation - at least 150 minutes of brisk walking each week - was associated with an average of 3.4 to 4.5 years longer life expectancy than no exercise.
The increase in longevity started to plateau around the equivalent of 300 minutes of brisk walking each week.
Being active and having a normal weight (BMI 18.5 – 24.9) was associated with a gain of 7.2 years of life, compared to being inactive and and having a high BMI - obese class II (BMI of 35 or higher).
Being inactive and normal weight was associated with 3.1 fewer years of life compared to being active and obese class I(BMI 30.9).
But people who were class II+ obese and active did not live longer than people who were normal weight and inactive. By comparison, long term smoking reduces life expectancy by about 10 years.
The authors, led by Steven Moore from the US National Cancer Institute, said that to their knowledge, the study was the first to estimate years of life lost combining physical inactivity and BMI.
"Our findings highlight the important contribution of physical activity to longevity," the study said.
But in recent decades, physical activity levels had declined in developed and developing countries.
The research findings "may help convince currently inactive persons that a modest physical activity programme is 'worth it' for health benefits, even if it may not result in weight control".
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