Regular vigorous physical activity could slow the progression of prostate cancer in older men, a study has found.
Prostate cancer can be a killer
The findings suggest working up a real sweat may help prevent men over 65 dying from the disease.
But the team from Harvard School of Public Health found men had to work out vigorously for at least three hours a week for it to have a positive effect.
The 14-year study, reported in the Archives of Internal Medicine, focused on data on 47,620 men in the US.
Previous research has suggested more physically active men may be at lower risk of prostate cancer.
However, the link has never been shown to be particularly strong.
The 47,620 men involved in the latest study were followed from 1986 to 2000.
Each was asked to provide information about how much exercise - such as hiking, jogging, cycling, swimming and racket sports - they took.
During 14 years of the study, 2,892 new cases of prostate cancer were diagnosed, including 482 advanced cases.
The researchers found that older men - aged 65 and over - who did regular, vigorous exercise were at a lower risk - almost 70% - of advanced and fatal cases of the disease.
However, no such association was found in younger men.
The researchers say that more work is needed to determine just how vigorous exercise may benefit prostate cancer patients.
Henry Scowcroft, of the charity Cancer Research UK, said it was not clear whether the study had shown a "cause and effect", or whether men who took more exercise were simply more health conscious.
He said: "This group might be more inclined to report symptoms to their doctor earlier and thus have their disease diagnosed before it becomes advanced.
"Given the well-documented benefits of a healthy lifestyle, we recommend that you take at least 30 minutes of moderate exercise five times a week.
"Having said that, older men should consult with their GP before embarking on any particularly vigorous exercise regime."
Chris Hiley, of the Prostate Cancer Charity, agreed.
She said: "We would caution that men with prostate cancer, many of whom might have other health problems associated with getting older, should seek advice from their GP before suddenly making such a change.
"What is clear is that regular exercise throughout life has benefits and this could be yet another example where steady and prolonged application is 'money in the bank' later in life."