People who put off regular exercise until they hit the age of 50 can still benefit from physical activity but it appears to take 10 years for the effects to kick in, Swedish researchers said on Friday.

A study of 2,205 Swedish men followed for more than 20 years from the age of 50 showed that exercise made no difference in premature death rates for at least a decade for those who waited until later in life to start physical activity.

"It has been shown that young people benefit from exercise but this is the first time we have been able to show that old people can also benefit from increasing their physical activity," Liisa Byberg, a researcher at Uppsala University in Sweden, said in a telephone interview.

"It's not too late to start."

The researchers put the volunteers into low, medium and high activity groups. About half the men reported a high level of exercise, corresponding to at least three hours of sport or heavy gardening each week.

About a third said they exercised moderately, such as taking walks and cycling, while the rest did little or no exercise, the researchers reported in the British Medical Journal.

Not surprisingly, death rates were highest among the sedentary group and lowest among the most active volunteers in the first five years of the study. But after 10 years people who began exercising at 50 had similar death rates to people in the high activity group.

The impact was similar to giving up smoking and the findings suggest further research to see what amount of physical activity makes a difference on health, the researchers said.

"There is an effect but there is a bit of a delay," Byberg said.