One of the major goals of exercise is to improve health. However, often enough the potential for harm from exercise is put into question, and sometimes for good reason. Be it the link between cycling and decreased bone density, the effects of ultra-endurance events on the brain, the burst of free radicals produced by exercise, or any number of other theorized or known health concerns, the questions are in place for good reason. One such question is how exercise affects cancer cell growth.

 

It’s no surprise that exercise is theorized to exacerbate cancer. Hormones associated with tissue growth, like growth hormone, IGF-1, insulin, and leptin, have been shown to be associated with higher cancer risk and the progression of existing cancer. In a recent study in PLoS ONE, researchers examined the interplay between exercise, hormones, and prostate cancer, which has been one of the most discussed types of cancer in recent literature.  

 

The researchers noted that long-term exercise was associated with reduced risk of cancer. These effects are related in part to the long-term hormonal response to exercise. Much like your heart rate response to cardiovascular exercise, over time your circulating hormones tend to decrease in response to exercise. In the long term, you’ll have less of these hormones in total. If you’re an avid exerciser, your overall hormone state is more inhospitable to prostate cancer, so your risk goes down.

 

However, the researchers in this study were more interested in the effects of acute exercise on hormones, rather than long-term exercise. The acute effects of exercise are quite different from the long-term effects. That is to say, when we exercise, the hormones supporting tissue growth come out in full force. For an athlete, the increase in hormones is usually a good thing, since it signals the repair and growth of damaged muscles. But for cancer cells this means growth too, and that’s a bad thing.

 

The researchers didn’t just expose cancer cells to these hormones, because they already knew what would happen in isolation: the cells would grow. Instead, they took blood from individuals at rest and those who had just exercised and exposed the cancer cells to the blood serum samples. This means they exposed the cancer cells to a much broader range of blood contents than just a few isolated hormones. They effectively exposed them to the state of the body post-exercise.

 

The results of the study were eye-opening. The serum of nine out of ten participants who had exercised actually inhibited cancer growth. Despite the increase in tissue-growing hormones, the cancer’s growth was slowed. When pooling the samples, the exercise serum resulted in a 31% inhibition to the growth of cancer. When injected into mice, the serum caused a delay in tumor formation.

 

Although some of the more potent hormonal outcomes of exercise, like growth hormone and IGF-1, may support cancer growth in isolation, this study shows they don't have the same effect when considered as a part of the whole post-exercise state. As it turns out, even acute exercise seems to be beneficial, at least at slowing the rate of existing cancer. The researchers concluded that this study dissuades fear of the effects of exercise on prostate cancer.

 

References:

1. Helene Rundqvist, et. al., “Effect of Acute Exercise on Prostate Cancer Cell Growth,” PLoS ONE 8(7), 2013.

 

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