The study was published on Friday on the website of the British Medical Journal (BMJ).
Men who began exercising after the age of 50 had the same life expectancy after 10 years as men who had always exercised, the researchers from Uppsala University said.
The study surveyed 2,205 men at age 50 in 1970 and divided into four groups (sedentary or low, medium or high physical activity levels). They were followed up at ages 60, 70, 77 and 82.
It showed that starting to exercise after the age of 50 was as beneficial as giving up smoking, but it had to be a regular regimen for five to 10 years for the positive effects to be observed.
“Increased physical activity in middle age is eventually followed by a reduction in mortality to the same level as seen among men with constantly high physical activity,” the study said.
“This reduction is comparable with that associated with smoking cessation,” it added.
The study noted that around half of middle aged men in Western countries do not exercise regularly.