Nutritional Pearls: Can Exercise Reduce Cancer Risk?

Sam is a 33-year-old man concerned about his weight. He has a BMI of 27 and, despite beginning regimen of biking and jogging several months ago, he has not lost any weight. At his most recent checkup, he asks if it is worth it to continue exercising, even when it is having no effect on his weight.

How do you advise your patient?
(Answer and discussion on next page)

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Answer: Regardless of weight loss, physical activity has many health benefits.

Physical health is not just about diet—physical activity is important as well. We know that exercise plays a role in weight loss and weight maintenance and can help prevent dementia and treat metabolic syndrome in older adults. Some research has suggested that exercise plays a role in cancer risk, as well, but the outcomes of that research have been mixed because of the small number of participants.

Fortunately, an international team of researchers, funded by the National Institutes of Health, performed a meta-analysis to assess the impact of leisure time physical activity on cancer risk.
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The Research

The authors grouped data from 12 prospective studies performed in the United States and Europe with a total of nearly 1.5 million participants, none of whom had been diagnosed with cancer at the start of their study.1 Over half of these studies specifically assessed moderate- and vigorous-intensity exercise by asking about time spent in such activities as walking, running, or swimming, while others asked only about vigorous-intensity activities or how often the individuals participated in these activities.

The authors could then categorize the amount, intensity, and duration of exercise in increasing percentiles, with the highest percentiles participating in the most vigorous physical activities for the greatest amount of time. They then compared the amount of physical activity in those who were diagnosed with any of 26 different types of cancers over the course of each study's follow-up period (averaging between 7 and 21 years) with those who did not.

The Results

Compared with those in the 10th percentile of exercise (those who exercised the least, and least vigorously), those in the 90th percentile of exercise reduced their risk by at least 20% for 13 different types of cancers, including esophageal cancer, liver cancers, lung cancer, kidney cancer, endometrial cancer, and myeloid leukemia. They also reduced their risk of myeloma, colon cancer, rectal cancer, bladder cancer, and breast cancer by between 10% and 20%. On the other hand, those who exercised the most were slightly more likely to develop prostate cancer and up to 40% more likely to develop malignant melanoma, a skin cancer. The authors theorize that this is due to many physical activities being done outside and the participants having much greater sun exposure.

More importantly, when the authors took BMI into account, most of the associations between greater and more vigorous exercise and lower risk of cancers did not change significantly: never greater than a 6% change in risk. That means that regardless of a participant's BMI, whether clinically underweight, of normal weight, overweight, or obese, those who exercised more still had a lower risk of cancer.

What’s the “Take-Home”?

Excess body weight is still linked with increased risk of heart disease, high blood pressure, and diabetes, but weight should not stop you from finding a physical activity you like. As the authors state, "...not all persons who engage in high levels of physical activity have low body weights."

It's clear that regardless of your weight, physical activity is good for you and appears to help reduce your risk of cancers of many kinds. Find an activity you like, whether it's walking, swimming, roller blading, cycling, or playing your Wii, and do it regularly. Even if you don't lose weight (and that need not be your goal), you'll still benefit in many ways—cancer is just one.

1. Moore S, Min-Lee I, Weiderpass E, et al. Association of leisure-time physical activity with risk of 26 types of cancer in 1.44 million adults [published online May 16, 2016]. JAMA Intern Med. doi:10.1001/jamainternmed.2016.1548.