Hundreds of previous studies have examined associations between physical activity and cancer risk and shown reduced risks for colon, breast, and endometrial cancers. However, these results have been inconclusive for most cancer types due to small numbers of participants in the studies.
In the new study, Steven Moore of the US National Cancer Institute and colleagues examined data from 1.44 million people, aged 19 to 98, from the United States and Europe, who were followed for a median of 11 years.
Participants were asked whether they did moderate or vigorous intensity activities in their free time, like walking, running or swimming, and how much physical activity they got.
During the study peroid, about 187,000 new cases of cancer occurred in the study participants.
The study confirmed that leisure-time physical activity, as assessed by self-reported surveys, was associated with a lower risk of colon (16 percent), breast (10 percent), and endometrial (21 percent) cancers.
The researchers also determined that leisure-time physical activity was associated with a lower risk of 10 additional cancers, with the greatest risk reductions for esophageal adenocarcinoma (42 percent), liver (27 percent), gastric cardia (22 percent), kidney (23 percent), and myeloid leukemia (20 percent).
Myeloma and cancers of the head and neck, rectum, and bladder also showed reduced risks that were significant, but not as strong.
Risk was reduced for lung cancer, but only for current and former smokers, and the reasons for this are still being studied.
Overall, a higher level of exercise was associated with a 7 percent lower risk of total cancer.
Most of the associations remained regardless of body size, suggesting that exercise acts through mechanisms other than lowering body weight to reduce cancer risk.
"Our results support that these associations are broadly generalizable to different populations, including people who are overweight or obese, or those with a history of smoking," said Moore.
"Health care professionals counseling inactive adults should promote physical activity as a component of a healthy lifestyle and cancer prevention."
The findings were published in the US journal JAMA Internal Medicine. (PNA/Xinhua)