The study adds reduction of risk of 13 cancers to the list of benefits that higher levels of moderate to vigorous exercise, such as swimming, have on health.
The international team of researchers - including investigators from the National Cancer Institute (NCI) in Bethesda, MD, and the American Cancer Society in Atlanta, GA - reports the findings in the journal JAMA Internal Medicine.
The analysis shows that the risk of developing seven types of cancer was at least 20 percent lower for the 10 percent most active participants, compared with the 10 percent least active.
The researchers confirmed the already known link between higher levels of exercise and reduced risk for colon, breast, and endometrial cancers, and added 10 other cancers to the list.
Smaller - but still significant - reductions were seen in myeloma and cancers of the head and neck, rectum, and bladder.
The researchers also found that in the most part, links between exercise and cancer were similar in normal and overweight people, and in smokers and people who never smoked.
However, while a reduced risk was found for lung cancer, this only appeared to be relevant to current and former smokers (as opposed to never-smokers). The researchers say the reasons for this are still being investigated.
Exercise should be key element of cancer prevention
The investigators say the findings bolster evidence that physical activity has a beneficial effect on cancer risk and support the idea that it should be a key element of public health efforts to prevent and control cancer.
First author Dr. Steven C. Moore, an investigator with the NCI whose research interests include physical activity, obesity and cancer, explains we already have evidence that leisure-time physical activity reduces risks of heart disease and death from all causes. Now, the new study adds many types of cancer to this list, and he notes:
"Furthermore, 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."
While hundreds of studies have shown the benefit of exercise on lowering cancer risk, in the main - apart from links to colon, breast, and endometrial cancers - the evidence for most cancer types has been somewhat inconclusive. The main reason for this is because the studies have not included enough people.
The new analysis examines a broad range of cancers, including rarer types. It pools data on 1.44 million people aged 19-98 from the US and Europe who were followed for about 11 years, during which 187,000 developed cancer.
The study defines leisure-time physical activity as exercise that people do at their own discretion - typically to improve and maintain health and fitness.
Such exercise includes moderate to vigorous activities, for example swimming, walking, and running. The mid-range of time spent per week on such exercise in the study was 150 minutes of moderate-intensity activity, which is around the minimum recommended in the US.
"Health care professionals counseling inactive adults should promote physical activity as a component of a healthy lifestyle and cancer prevention."
Dr. Steven C. Moore