Exercising might lower cancer risk

A study has found people who regularly exercise prove to be less likely to develop or die from cancer than people who do not

The relation between exercise and cancer has long both intrigued and puzzled oncologists and exercise physiologists.

Exercise is associated with lowered risks for many types of cancer. In epidemiological studies, people who regularly exercise prove to be much less likely to develop or die from the disease than people who do not. At the same time, exercise involves biological stress, which typically leads to a short-term increase in inflammation in body. Inflammation can contribute to elevated risks for many types of cancers. Now, a study in mice might offer some clues into the exercise-cancer paradox. It suggests exercise could change how the immune system deals with cancer by boosting adrenaline, certain immune cells and other chemicals that together can reduce the severity of cancer or fight it off altogether.

To try to better understand how exercise can both elevate inflammation and simultaneously protect the body against cancer, scientists at the University of Copenhagen in Denmark and other institutions decided to closely examine what happens inside mice at high risk for the disease. The new study, published this month in Cell Metabolism, they began by gathering a group of adult lab mice. These animals generally like to run.

The scientists then implanted melanoma skin cancer cells into the mice before providing half of them with running wheels in their cages while the other animals remained sedentary. After four weeks, far fewer of the runners had developed full-blown melanoma than the sedentary mice and those who had been diagnosed with the disease showed fewer and smaller lesions. They also were less prone to metastases, even if scientists injected some of the cancer cells into their lungs to stimulate metastases.

In effect, running seemed to have at least partially inoculated the mice against the cancer. Next, the scientists undertook the far more challenging task of reverse-engineering the process by which exercise might be helping to fight off the tumours. To start, they drew blood from both the exercising and sedentary animals and cells from any tumours in both groups. Then they looked microscopically at how the various samples were different.

As expected, they found much higher levels of the hormone adrenaline in the blood of the exercising animals, especially right after they had been working out on the wheels but also at other times of the day. The body releases adrenaline in response to almost any type of stressful experience, including exercise.

They also found higher levels of interleukin-6 in the blood of the runners. This is a substance that is released by working muscles and is believed to both increase and decrease inflammation in the body capriciously, depending on where and how it goes to work.

Perhaps most important, they found much higher numbers in the bloodstreams of runners than in the sedentary mice of a type of immune cell named natural killer cells that are known to be potent cancer fighters.

©2016 The New York Times News Service