We’ve known for years that exercise reduces the risk of several types of cancer but we weren’t always sure exactly how. New research has identified several mechanisms:
1. Exercise and Immunity
Exercise boosts the immune system. More specifically, exercise stimulates the release of the hormone epinephrine, which helps to circulate natural killer (NK) cells in tumors. These specialized white blood cells act as our immune system’s assassins, infiltrating tumors and causing them to shrink.
2. Exercise and Inflammation
Study after study has shown that long-term exercise programs reduce markers of inflammation, a critical component of tumor progression. High intensity interval (HIIT) training, in particular, is known to stimulate the release of myokines from the muscle cells. These chemical messengers inhibit the effects of inflammatory molecules produced by body fat.
3. Exercise and Insulin
Physical activity reduces the amount of insulin in our blood. Scientists believe insulin can turn on signals that tell cells to multiply. Since cancer begins when cells multiply out of control, lowering insulin levels could help stop some types of cancer from developing. Elevated insulin leads to over-stimulation once a cancer cell has emerged, promoting proliferation, migration, and invasiveness of cancer cells through multiple pathways.
Research has shown that prostate cancer incidence is more than 2.5 times higher in men with the highest blood insulin levels. Stomach cancer risk is nearly 70% higher for people with blood insulin levels in the middle third, compared with those in the bottom third and over 100% higher in those with the top one-third of insulin levels! And cancers of the female reproductive system seem especially sensitive to elevated insulin levels.
4. Exercise and Estrogen
Exercise lowers blood estrogen levels. This is important, as women with high estrogen levels in their blood have increased risk for breast cancer. In fact, dozens of studies have shown that women who exercise have a 30 to 40 percent lower risk of breast cancer than their sedentary peers. Older women also need to be concerned about estrogen. After menopause the hormone is produced by fat cells. Women who exercise have less fat and therefore produce less estrogen.
5. Exercise and Leptin
Exercise affects leptin levels. Leptin is a hormone produced by the fat cells in your body. Leptin controls your metabolism, hunger, and energy expenditure. Leptin levels rise after you’ve eaten – as does your metabolic rate – and your brain then sends a signal to the rest of your body that you’re full. This is good. But if you’re always in a caloric surplus, you can become leptin resistant. If you eat a diet high in sugar (especially fructose), grains, and processed foods, the sugar gets metabolized in your fat cells and the fat releases leptin. Over time, these surges cause your body to become resistant to leptin in the same way it can become resistant to insulin.
When leptin levels are high, cancers survive better, grow faster, and spread more. There’s evidence that leptin increases levels of insulin and estrogen, both of which promote cancer growth. Research has shown that breast cancer cells express unusually high levels of leptin and its receptors. Additionally, it’s been shown that when leptin is high, cancer drugs like Tamoxifen do not work as well to block estrogen. Exercise – especially sprinting and weight training – can help restore proper leptin function and even reverse leptin resistance.
6. Exercise and our DNA
Exercise can literally “turn off” genes that are associated with diseases like cancer. This typically happens through a process called methylation, which is when a clusters of atoms, known as methyl groups, attach to the outside of a gene affecting how it sends and receives signals from the body.
When those methyl groups are removed, it’s referred to as demethylation. If this cycle gets disrupted, you get sick. DNA hypomethylation can be found early in carcinogenesis and is also associated with tumor progression; hypermethylation is also thought to be a cancer culprit. For example, these processes can silence a gene (CACNA2D3) that would
otherwise suppress tumors. Exercise can reverse hypermethylation and restore normal gene function.
Past research has suggested that a single bout of exercise can produce immediate changes in the methylation patterns of certain genes in muscle cells. A more recent study has demonstrated a long-term effect, with scientists noting significant methylation changes on thousands of sites on the genome of muscle cells in response to single-leg training (no changes were seen in the unexercised leg). Gene expression was noticeably increased in thousands of muscle-cell genes, particularly those that play a role in energy metabolism, insulin response, and inflammation within muscles.
While the health benefits of exercise typically focus on its proven cardiovascular effects, increasing evidence supports its therapeutic value for those seeking to prevent and treat cancer as well. Clearly, the benefits exert themselves through multiple pathways – cellular, hormonal, genetic – and go beyond the obvious weight management considerations. While any type of exercise will be beneficial, the intensity, duration, and frequency are important factors and guidance from a qualified fitness professional should be sought when trying to safely and effectively apply these research findings to a new or existing exercise routine.