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New Study Links Leisure-Time Physical Activity to Reduced Risk for 13 Types of Cancer

Ties between moderate-to-vigorous physical activity and cancer prevention may be much stronger than previously thought: according to a new large-scale study, physically active individuals drop their risk of developing 13 different types of cancer by as much as 20%, including risk reduction for 3 of the 4 most-commonly diagnosed cancers worldwide. Additionally, that preventive tie isn't significantly lessened by a higher Body Mass Index (BMI) or smoking.

The study, published in the May 16 issue of JAMA Internal Medicine (abstract only available for free), used pooled data from 8 studies in the United States and 4 in Europe to look at the relationship between physical activity (PA) and development of 26 types of cancer among 1.44 million participants who had no cancer at baseline. Individuals tracked in the studies ranged in age from 18 to 98 (average age, 59), with 57% female. A total of 186,932 cancers were included.

For their analysis, authors of the JAMA study defined moderate-intensity PA as activity with an intensity of 3 or more metabolic equivalents (METs), and vigorous-intensity PA as 6 or more METs. Because the individual studies varied somewhat in the ways they obtained information on PA, researchers for the current study translated PA rates into percentiles, and focused on differences between individuals in the 10th and 90th percentiles.

Here's what they found:

Higher levels of leisure-time PA reduced cancer risk in 13 of 26 types of cancer.
For individuals in the 90th (or higher) percentile of PA rates, researchers reported a greater than 20% drop in risk for esophageal, liver, lung, and kidney cancers, as well as cancers of the gastric cardia and endometrium. Risk of myeloma, as well as breast, colon, rectal, and bladder cancer dropped by 10%-20%. Overall, higher levels of PA were associated with a 7% lower risk for total cancer.

Cancer risk reduction through PA was generally independent of BMI.
For the most part, individuals with a higher BMI (25 or greater) who engaged in significant amounts of moderate-to-vigorous PA also saw a reduction in risk similar to their lower-BMI counterparts-including lung and endometrial cancers.

The protective effects of PA also worked for current and former smokers-with exceptions.
Other than rates of lung cancer and myeloma, researchers found little evidence that smoking (or having smoked) affected the ability of PA to reduce risk among the 13 types of cancers that registered reductions.

Risk of melanoma and prostate cancer increased slightly for the more active, but probably not because of the PA itself.
Researchers recorded upticks in risk for melanoma and prostate cancer among the high-PA groups, but they believe the reasons behind those differences may be due to factors outside the PA itself. Authors theorize that individuals with high PA rates are more likely to be screened for prostate cancer, and many individuals with high rates of PA engage in outdoor activities that increase exposure to the sun (and risk of sunburn). They think these factors may account for the associated risk.

A JAMA Internal Medicine editorial that accompanies the research article describes the study as "innovative" and one that "provides clarity to the potentially important role of leisure-time activity in cancer prevention." The editorial states that "these exciting findings … underscore the importance of leisure-time physical activity as a potential risk reduction strategy to decrease the cancer burden in the United States and abroad."

Editorial authors also call for more studies of the PA-cancer prevention relationship, including whether the positive effects are only realized when individuals have been physically active throughout their lives, or if they can be achieved by beginning a higher level of PA later in life.

Researchers believe their work is the largest-ever study on the relationship between PA and cancer risk, and the findings expand on previous evidence of a relationship between increased PA and reduced risk for colon, breast, and endometrial cancers.

The researchers are also encouraged by the overall reach of the reductions. "Our results support that these associations are broadly generalizable to different populations, including overweight or obese individuals, or those with a history of smoking," authors write. "These findings support promoting physical activity as a key component of population-wide cancer prevention and control efforts."