Some studies suggest that regular exercise may lower the risk of some forms of cancer. Who wouldn’t want that extra benefit, especially with cancer being in the top five causes of premature death? Yet there are still unanswered questions. What types of cancer does exercise lower the risk of and how much exercise do you need to reduce the odds of getting it? You might also wonder what form of exercise is most protective against cancer. Is a strength-training workout the key to lowering your cancer risk or are aerobic workouts more beneficial?
What better way to look at this issue than to combine multiple studies and see how strong the link between exercise and physical activity is? That’s what a group of researchers did—they pooled the results of nine studies involving 755,459 people. They found that exercising between 2.5 and 5 hours per week reduced the risk of several cancers including liver cancer, multiple myeloma, kidney cancer, cancer of the uterus, and breast cancer. Some reduced risk was gender-specific. For example, exercise lowered the risk of colon cancer in men only and non-Hodgkin lymphoma in women only.
There are some caveats. When the researchers controlled for body weight and BMI, exercise didn’t significantly reduce the risk of uterine cancer in women. Cancer of the uterus is fueled by estrogen and women who are overweight or obese have higher circulating levels of estrogen to drive cancer growth. However, exercise helps with weight control, so it is still beneficial for uterine cancer prevention, but the real benefits come from avoiding obesity. Plus, lengthy periods of aerobic exercise lowers estrogen, a hormonal driver of uterine of cancer.
How Much Can Exercise Reduce the Risk of Cancer?
The degree of risk reduction varies with the type of cancer. In the study, it ranged from a low of 6 to 10% for breast cancer up to an 18 to 27 % risk reduction for liver cancer. This study also suggests that you don’t need an extraordinary amount of exercise to reduce your risk of developing some types of cancer.
In fact, the study concluded that you need between 7.6 and 15 MET-hours per week at a minimum to lower the risk of developing the types of cancer mentioned above. The link held even when the researchers controlled for other factors that affect cancer risks such as lifestyle habits and body weight.
Since we’re referring to MET-hours of exercise, you might also wonder how exercise intensity impacts cancer prevention? Vigorous workouts burn more calories and create more of an afterburn, but how does exercise intensity affect cancer risk?
At least in this study, researchers found that high-intensity exercise was less effective for reducing the risk of colon and uterine cancer than moderate-intensity exercise. However, one study showed that brief, vigorous exercise, such as high-intensity interval training, may reduce the risk of breast tumors. In a study carried out in rodents, intense exercise cut the formation of breast tumors by 50%.
On a down note, the current study found that exercise didn’t lower the risk of all cancers. Working up a sweat did not alter the risk of cancers of the gallbladder, rectum, bladder, and small intestine. However, it’s encouraging that exercise may reduce the risk of some of the most common forms of cancer, including breast and colon cancer.
How Does Exercise Reduce the Risk of Some Cancers?
It’s one thing to say that physical activity lowers the risk of cancer, but you might wonder why. There are several possible mechanisms. For one, staying physically active keeps body weight in check. Obesity is a risk factor for several cancers, including cancers of the breast (post-menopausally), cancer of the uterus, esophageal cancer, liver cancer, kidney cancer, and gastric cancer.
Studies also show that exercise in moderation lowers markers of inflammation, suggesting it has an anti-inflammatory effect. As with many health conditions, inflammation damages tissue and can drive the growth of malignancies. Another benefit of exercise is how it affects insulin sensitivity. Exercise boosts how sensitive cells are to insulin and lowers circulating insulin levels. That’s important since insulin and insulin-like growth factor (IGF-1), produced by the liver in response to insulin, fuel the growth of cancers. In fact, people with type 2 diabetes and metabolic syndrome have a higher risk of developing certain forms of cancer, including cancers of the pancreas and colon.
Long periods of aerobic exercise also lower the level of sex hormones, like estrogen and testosterone, that impact the risk of developing some cancers. These include breast and uterine cancer in women and prostate cancer in men. In women, exercise also boosts the levels of sex hormone-binding globulins that carry estrogen and testosterone through the body. When you have more sex hormone-binding globulins there’s less estrogen and testosterone available to tissues to boost cancer growth.
Finally, exercise upregulates the body’s natural antioxidant defenses and that may help prevent cell and tissue damage, including DNA mutations, that spur the development of cancer.
A mechanism by which exercise reduces the risk of cancer you hear less about is its effect on AMPK, a cell’s energy sensor. When your fuel stores run low, as during exercise or fasting, cells produce more AMPK to mobilize more energy for fuel-starved muscle cells. AMPK has another benefit too. Some studies show it suppresses the growth of some tumors. So, anything that raises AMPK, like aerobic exercise, may help keep cancer in check. This may also explain why some studies show that fasting has anti-cancer benefits.
The Bottom Line
Exercise may slash the risk of some forms of cancer through a variety of mechanisms and it doesn’t take an inordinate amount of exercise to get the benefits. Staying active also lowers the risk of obesity, another risk factor for at least 13 cancers. So, now you have another compelling reason to stay active and work up a sweat!
References:
- org. “Does the Intensity of Physical Exercise Affect Cancer Risk?”
- com. “How Exercise Fights Inflammation”
- Harvard Gazette. “Growth Factor Raises Cancer Risk”
- Future Oncol. 2010 Mar; 6(3): 457–470. doi: 10.2217/fon.09.174.
- MD Anderson Cancer Center. “Moderate vs. vigorous exercise for cancer prevention”
- “Brief, Intense Exercise May Keep Breast Cancer at Bay”
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