Can exercise help lower cancer risk?
Whether or not you drop pounds, you can at least get more active. Though the evidence that this will lower your cancer risk is inconclusive so far, there are encouraging signs.
For instance, in a study published in 2006, researchers considered the effects of a 12-month program of aerobic exercise. The participants were 100 women and 102 men, ages 40 to 75 years, all healthy and having undergone a colonoscopy within the last three years. Before the study, they had led lives of sedentary ease, and now half were asked to continue their normal exercise habits, such as they were.
But the other half worked up to working out six days a week, for 60 minutes a day, mostly on treadmills and stationary bikes. Men who successfully completed the program showed a significant lowering of two biomarkers associated with colon cancer risk — increased proliferation of cells in the lining of the colon and an extension of the zone where such proliferation takes place. For women, there was no change.
The study couldn’t show that people actually reduced their cancer risk — it only measured signs that have been associated with cancer risk. But these signs pointed in the right direction.
Better news for women comes from another 12-month study of exercise effects, published in 2004. Participants — 173 postmenopausal women who were formerly sedentary and overweight — engaged in moderate-intensity exercise for 45 minutes a day, five days a week. The exercisers showed a decline in estrogens that have been associated with an increased risk of breast cancer — though only if the exercise led to a decrease in their percentage of body fat by at least 2%.
The difference between simply losing weight and losing body fat is critical, says Jennifer Klemp, an assistant professor of medicine and associate director of the Breast Cancer Survivorship Center at the University of Kansas Medical Center in Westwood. “You can be skinny and still be fat.”
Some evidence for that comes from a 2006 study that looked at estrogen along with two other hormones that are known to be risk factors for postmenopausal breast cancer. Levels of these hormones were found to be significantly higher in women who had both a high body-mass index (29 or more) and low physical activity compared with women who were either of fairly healthy weight, active, or both. These results suggest that an overweight but active woman may possibly be at lower risk for postmenopausal breast cancer than an overweight couch potato.
