Engaging in recommended amounts of leisure-time physical activity is linked to a lower risk for seven types of cancers, according to a review of studies which may lead to new intervention strategies against the malignant disease.

The researchers, including those from the National Cancer Institute in the US, said while physical activity has been associated with a lower risk of several cancers in previous studies, the relationship between recommended amounts of it have not been particularly associated with cancer risk.

In the current study, published in the Journal of Clinical Oncology, the scientists pooled data from nine prospective cohorts, involving a total of 750,000 adults, with self-reported leisure-time physical activity, and follow-up for cancer incidence.

They assessed the relationship between physical activity with incidence of 15 types of cancer.

According to the researchers, 2.5 to 5 hours per week of moderate-intensity activity, or 1.25 to 2.5 hours per week of vigorous activity is recommended.

Moderate-intensity activities, they explained, are those where a person moves fast enough to burn off three to six times as much energy per minute as sitting quietly (3 to 6 METs), and vigorous-intensity activities burn more than 6 METs.

On analysing the data, the researchers found that engaging in recommended amounts of activity -- 7.5 to 15 MET hours a week -- was associated with a statistically significant lower risk of seven cancer types.

They added that the risk reduced more with increased MET hours.

Physical activity, the study said, was associated with a lower risk of colon cancer in men -- 8 per cent for 7.5 MET hours per week, and 14 per cent for 15 MET hours a week.

According to the study, engaging in recommended levels of physical activity was also associated with lower incidence of other cancers such as female breast cancer (6-10 per cent), endometrial cancer (10-18 per cent), kidney cancer (11-17 per cent), and liver cancer (18-27 per cent).

Although the study included 750,000 patients, the study had a few limitations including that the participant numbers were limited for some cancers, they were primarily white, and the physical activity measures were not very detailed, with the authors relying on self-reported accounts.

"These findings provide direct quantitative support for the levels of activity recommended for cancer prevention and provide actionable evidence for ongoing and future cancer prevention efforts," the researchers concluded in the study.

"Physical activity guidelines have largely been based on their impact on chronic diseases like cardiovascular disease and diabetes. These data provide strong support that these recommended levels are important to cancer prevention, as well," said Alpa Patel, study co-author from the American Cancer Society.