Spending time in the great outdoors could be a reason why exercise may prevent cancer, Professor Tim Oliver, founder of male cancer charity Orchid has said.

Professor Oliver said the higher vitamin D levels could be the reason. Recent research by researchers at the University of California, and the Harvard School of Public Health suggests that brisk walking or vigorous physical activity, could help slow prostate cancer.

Commenting on the research, Professor Oliver said: "Briskness of walking is a somewhat imprecise term, but all studies of the health benefit from exercise, whether it is cardiac disease, depression or cancer, suggests that it has to be sufficient to get the heart beating faster than normal."

"While it makes sense for preventing cardiac disease, it is not immediately obvious how it prevents cancer and depression," he said.

Professor Oliver, did however, offer a reason as to why exercise could potentially, have a protective effect against the disease.

"It is possible that one of the main ways that exercise prevents cancer is that, as it is mostly outdoors, the patients whose cancers grow slower, do so because they have higher vitamin D levels," he explained.