The analysis, published in PLOS Medicine, pooled self-reported data on physical activities and body mass indexes (BMIs) -- a ratio of weight to height -- from some 650,000 people aged 40 and older enrolled in one Swedish and five US studies.
"This result may help convince currently inactive people that a modest physical activity program may have health benefits, even if it does not result in weight loss," said a summary of the analysis headed by Steven Moore of the US National Cancer Institute.
The researchers used the studies to calculate the boost to life expectancy linked to specific levels of physical activity and found that brisk walking for up to 75 minutes per week was associated with a gain of 1.8 years in life expectancy.
"Being active -- having a physical activity level at or above the World Health Organization-recommended minimum of 150 minutes of brisk walking per week -- was associated with an overall gain of life expectancy of 3.4 to 4.5 years," the summary said.
Overall, the researchers concluded that less physical activity was linked with a shorter life expectancy no matter a person's body mass index.
"More leisure time physical activity was associated with longer life expectancy across a range of activity levels and BMI groups," the abstract of the analysis concluded.
However, being active and having a normal body mass index (of 18.5 to 24.9) was associated with a gain of 7.2 years of life compared to people who are inactive and obese with a body mass index of 35 or above.
On the other hand, being inactive and normal weight was linked to 3.1 fewer years of life compared to those who are active but class I obese and have a BMI of 30-34.9.
"These findings suggest that participation in leisure time physical activity, even below the recommended level, is associated with a reduced risk of mortality compared to participation in no leisure time physical activity," the summary said.
"The findings also suggest that physical activity at recommended levels or higher may increase longevity further, and that a lack of leisure time physical activity may markedly reduce life expectancy when combined with obesity."