In the minds of many cancer is a scary word. Fortunately, treatment for many types of cancer is improving and people are living longer, fuller lives with this disease where cells multiply out of control. Unfortunately, treatments for cancer, including radiation and chemotherapy, have side effects, and it’s something most people don’t want to go through. That’s why prevention is the best medicine! Not all cancer be prevented. However, studies suggest that regular physical activity can lower the risk of some types of cancer but how many and which ones?
What Cancers Does Exercise Lower the Risk Of?
A 2016 study published in JAMA Network looked at the relationship between exercise and cancer. This was a prospective study that looked back at the exercise habits of participants and whether they later developed cancer. Specifically, the researchers determined the frequency with which people did leisure-time physical activity including running, cycling, swimming, and brisk walking. What adds to the credibility of this study is that it is a meta-analysis, a compilation of multiple studies. A meta-analysis pools the results of a variety of well-conducted, independent research studies and looks for trends. This study pooled data from 1.44 million people and followed them for more than 11 years.
When the researchers compared the cancer incidence of the participants to their level of physical activity (high versus low), they found participants who spent more time engaged in physical activity and those who exercised with more intensity had a lower incidence of 13 cancers, including cancers of the liver, esophagus, lung, stomach, kidney, uterus, colon, rectum, bladder, kidney, and head and neck. Being physically active was also correlated with a reduced risk of myeloid leukemia and multiple myeloma. In addition, other studies show high levels of physical activity lowers the risk of breast cancer. In the study, researchers statistically corrected for the body weight of the individuals. Even after controlling for body weight, exercise was associated with a lower risk of 10 of these cancers.
On the downside, the study found that men who were more physically active had a higher risk of prostate cancer and both sexes developed malignant melanoma more often. The malignant melanoma link is probably because people who exercise outdoors get more sun exposure. Melanoma, a serious form of skin cancer that can spread to other organs is strongly linked to sun exposure. It’s not as easy to explain why exercise is linked with a higher prostate cancer risk.
Some of the most dramatic risk reduction was for esophageal cancer. High levels of physical activity reduced the risk of this cancer by 42%. Subjects who exercised more also enjoyed a 26% lower risk of lung cancer and a history of smoking only modestly altered this association. Exercise also reduced the risk of liver cancer by 27%. At the low end, working out only decreases the risk of bladder and rectal cancer by 13%. Still, any risk reduction is good!
How Does Exercise Reduce the Risk of Cancer?
One reason exercise may lower the risk of cancer is the effect it has on body weight. Staying physically active is a lifestyle habit that helps prevent weight gain and improve body composition. A number of cancers on this list are associated with obesity, including cancers of the uterus, esophagus, liver, kidney, and stomach. You might question whether the benefits of exercise are indirect through controlling body weight rather than a direct effect of the exercise itself. But in this study, the link between physical activity and reduced cancer risk was not strongly dependent on body mass index (BMI) except cancers strongly associated obesity such as cancer of the uterus, liver, stomach, and kidney. So, exercise has benefits for cancer prevention that extend beyond its impact on body weight.
Another probable mechanism is a reduction in inflammation. There’s growing awareness that inflammation plays a key role in a variety of chronic health problems, including cardiovascular disease, type 2 diabetes, and even cancer. As the National Cancer Institute points out, chronic inflammation can lead to DNA damage that can over time trigger cancer. Inflammation can come from a variety of sources such as a chronic infection, chronic inflammatory diseases, and obesity. Fat cells produce inflammatory chemicals that boost inflammation. Studies show moderate physical activity has an anti-inflammatory effect that helps reign in low-grade inflammation and you can get the benefits with as little as 20 minutes of physical activity daily.
Another reason exercise may lower the risk of certain cancers is by reducing insulin and insulin-like growth factor one (IGF-1). Both aerobic exercise and resistance training help with blood sugar control and improve insulin sensitivity, leading to lower insulin levels. This is important since insulin and IGF-1 act as growth factors for cells and tissues, including malignant ones. In fact, people who have type 2 diabetes and higher insulin levels are at greater risk of developing some forms of cancer. Other ways exercise may help with cancer prevention is by its impact on hormones like estrogens in women. High levels of estrogen are associated with cancer of the uterus and breast. Finally, moderate exercise may help by reigning in oxidative stress that damages a cell’s DNA. Once DNA is damaged, it creates conditions that are ripe for cancer to form.
The Bottom Line
It’s encouraging that exercise is linked with a lower risk of so many cancers! Plus, we know it’s good for the cardiovascular system, brain, and other systems as well. So, now you have another reason to lace up your exercise shoes and work up a sweat. As if you needed another one!
References:
· JAMA Intern Med. 2016;176(6):816-825. doi:10.1001/jamainternmed.2016.1548.
· National Cancer Institute. “Chronic Inflammation”
· Medical News Today. “Just 20 minutes of exercise enough to reduce inflammation, study finds”
· LiveScience.com. “How Exercise Fights Inflammation”
· J Sports Sci. 2014;32(15):1435-45. doi: 10.1080/02640414.2014.900692. Epub 2014 Apr 14.
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