Physically Active People Have Lower Colon Cancer Risk

By Lisa Rapaport

August 13, 2019

(Reuters Health) - People who exercise regularly may be less likely to develop precursors to colorectal cancers, a research review suggests.

Compared to people who get the smallest amount of physical activity, individuals who get the most exercise are 23% less likely to develop precancerous neoplasias that can sometimes progress into full-blown colorectal cancer. And, regular exercisers are also 27% less likely than sedentary people to develop the most aggressive types of precancerous neoplasias with the most potential to progress to full-blown cancer.

"This gives us a strong support to promote exercise for prevention of colorectal neoplasia," said Martin Wong, senior author of the study and a researcher at the Chinese University of Hong Kong.

"Of course, there are other ways for those who are not willing or unable to increase physical activity levels (to lower their risk), including quitting smoking, limiting intake of processed meat, and maintaining a healthy body weight," Wong said by email.

Globally, colorectal cancer accounts for 10% of all new cancer cases and 9% of all cancer deaths, Wong and colleagues note in a paper in the British Journal of Sports Medicine, online July 11.

While previous research has linked regular exercise to a lower risk of colorectal cancer, researchers don't have a clear picture of the relationship between physical activity and the precancerous growths that can turn into tumors, the study team notes.

In the current study, more exercise was tied to a lower risk of precancerous colorectal growths in both men and women and for a variety of exercise routines.

One drawback of the study is that it relied on data from smaller studies that weren't controlled experiments - so they couldn't prove more exercise causes fewer cancer cases.

Some of the smaller studies in the analysis also relied on participants to report their own levels of activity instead of using objective measures like accelerometers to assess exactly how much exercise people got.

It's possible that regular exercise might help reduce the risk of colorectal tumors by accelerating digestion, which might reduce the amount of time the intestinal lining is exposed to acid or cancer-causing agents people ingest, the study team writes.

Regular physical activity might also help prevent colorectal tumors by improving the body's ability to use the hormone insulin to turn sugars in the diet into energy, reducing blood sugar levels, the study authors note.

Even if the study doesn't show why exercise prevents cancer, it does add to a large and growing body of evidence suggesting that people who get more physical activity may be less likely to get certain types of tumors, said Vandana Sheth, a spokesperson for the Academy of Nutrition and Dietetics who wasn't involved in the study.

"Physical activity is inversely associated with any type of colorectal neoplasia in both men and women," Sheth said by email. "Increasing physical activity and decreasing sedentary behavior can have a significant positive impact on our overall health especially in terms of colorectal neoplasia."


Br J Sports Med 2019.