Higher levels of leisure-time activity may boost protection against a wide range of cancers, according to a new analysis of research from the US and Europe.
Based on data from 12 previous studies involving a total 1.44 million people, researchers found that with few exceptions, high versus low amounts of moderate to vigorous activity meant lowered risk for 13 out of 26 types of cancer.
The results include a 42 per cent lower risk of esophageal cancer, 27 per cent lower risk of liver cancer, 26 per cent lower risk of lung cancer and a 23 per cent lower risk of kidney cancer.
Even after adjusting for body weight, Dr. Steven C. Moore of the National Institutes of Health in Rockville, Maryland, and his colleagues found lowered risk for 10 of the 13 cancers with higher levels of leisure-time physical activity. After factoring in smoking, they found it only affected the risk of lung cancer, but not other smoking-associated cancers.
Higher levels of activity were tied to a 27 per cent increased risk of malignant melanoma, however, and a slightly increased (5 per cent) rise in prostate cancer risk.
"Our results support that these associations are broadly generalizable to different populations, including overweight or obese individuals, or those with a history of smoking. These findings support promoting physical activity as a key component of population-wide cancer prevention and control efforts," the researchers conclude in JAMA Internal Medicine.
Dr. Moore did not respond to a request for comment.
The study team looked at physical activity levels across the various studies in terms of Metabolic Equivalents of Task, or METs, representing the amount of energy expended per minute in a specific activity. For example, resting expends 1 MET per minute, moderate activity like walking uses 3 to 5.9 METs and vigorous exercise like running uses more than 6 METs.
The studies included in the analysis asked participants about specific activities like walking, running or swimming, or they quantified overall weekly participation in moderate and vigorous activities. The middle-ground for most participants worked out to eight METs per hour per week, or about 150 minutes of moderate activity like walking.
The design of this analysis is "probably one of the strongest ... we could have," said Dr. Marilie D. Gammon, of the University of North Carolina, Chapel Hill, senior author of a commentary accompanying the study.
"The study authors also looked at a lot of rare tumours. In some ways they were able to confirm what we've seen in the more common tumours, but they also report on tumours that have been much harder to nail down. I think this is good news, especially when it comes to the rare tumour types. It gives us hope that (physical activity) could be an important public health strategy for risk reduction."
What's needed now is more research to determine what mechanisms are involved in risk reduction, she added. "Physical activity is just one of the cluster of healthy behaviours. It's hard to know which healthy behaviour it is (that leads to risk reduction)."