Men who exercise daily could halve their risk of prostate cancer, a major study has found.
Experts said regular activity - which can include gardening or walking - has a "far larger" protective effect than previously thought.
A team funded by the World Cancer Research Fund (WCRF) and Cancer Research UK used a robust method of measuring physical activity among 79,148 men with prostate cancer and 61,106 without.
The study, which mainly involved men over the age of 50, found those that were the most active had a 51 per cent reduced risk of prostate cancer compared with those who were the least active.
Researchers compared the 16 per cent who were most active with the 16 per cent who were most sedentary.
The most active men would be expected to meet NHS guidelines which recommend around 2 and a half hours exercise weekly, or 20 minutes a day.
In the UK, around one in six men will be diagnosed with prostate cancer during their lifetime.
The WCRF said this risk could drop to one in 12 for men who are the most physically active.
Dr Sarah Lewis, senior lecturer in genetic epidemiology at Bristol Medical School and lead author of the research, said: "Our findings suggest that the more active you are, the better.
"We would recommend that men are as physically active as they can be.
"Our evidence suggests being active will be beneficial in terms of their prostate cancer risk.
"But it doesn't have to be vigorous activity or playing team sports, you just have to move about.
"Being active could be things such as gardening, walking or other activities that you can build into your daily routine."
The study examined particular genes linked to exercise, to identify the most active men, and compare their disease rates with those of less active participants.
Dr Lewis said: "This study is the largest-ever of its kind which uses a relatively new method that complements current observational research to discover what causes prostate cancer.
"It suggests that there could be a larger effect of physical activity on prostate cancer than previously thought, so will hopefully encourage men to be more active."
Dr Anna Diaz Font, head of research funding at the WCRF, said: "Up till now, there has only been limited evidence of an effect of physical activity on prostate cancer.
"This new study looked at the effect of 22 risk factors on prostate cancer, but the results for physical activity were the most striking.
"This will pave the way for even more research, where similar methods could be applied to other lifestyle factors, to help identify ways men can reduce their risk of prostate cancer."
Prostate cancer mostly affects men over the age of 50 and risk factors include having a family history of the disease.
Almost 48,000 men in the UK are diagnosed with prostate cancer each year and it kills almost 12,000 men annually.
The study was published in the International Journal of Epidemiology.