Fight Aging!

Why does physical exercise reduce cancer risk and improve cancer outcomes? Researchers here propose that the mechanism of interest involves an improved capacity for cell destruction on the part of cytotoxic T cells. Cancer is an age-related condition in large part because the efforts of the immune system are vital in cancer suppression, and because the immune system declines in effectiveness with age. Cancer incidence correlates very well with the age-related atrophy of the thymus, the organ responsible for maturation of T cells. The resulting reduction in the supply of naive T cells capable of tackling new threats, such as newly cancerous tissue, is harmful to health in later life.

Prior research has shown that physical activity can prevent unhealth as well as improve the prognosis of several diseases including various forms of cancer. Exactly how exercise exerts its protective effects against cancer is, however, still unknown, especially when it comes to the biological mechanisms. One plausible explanation is that physical activity activates the immune system and thereby bolsters the body's ability to prevent and inhibit cancer growth.

Researchers expanded on this hypothesis by examining how the immune system's cytotoxic T cells, that is white blood cells specialized in killing cancer cells, respond to exercise. They divided mice with cancer into two groups and let one group exercise regularly in a spinning wheel while the other remained inactive. The result showed that cancer growth slowed and mortality decreased in the trained animals compared with the untrained. Next, the researchers examined the importance of cytotoxic T cells by injecting antibodies that remove these T cells in both trained and untrained mice. The antibodies knocked out the positive effect of exercise on both cancer growth and survival, which according to the researchers demonstrates the significance of these T cells for exercise-induced suppression of cancer. The researchers also transferred cytotoxic T cells from trained to untrained mice with tumors, which improved their prospects compared with those who got cells from untrained animals.

To examine how exercise influenced cancer growth, the researchers isolated T cells, blood and tissue samples after a training sessions and measured levels of common metabolites that are produced in muscle and excreted into plasma at high levels during exertion. Some of these metabolites, such as lactate, altered the metabolism of the T cells and increased their activity. The researchers also found that T cells isolated from an exercised animal showed an altered metabolism compared to T cells from resting animals. In addition, the researchers examined how these metabolites change in response to exercise in humans. They took blood samples from eight healthy men after 30 minutes of intense cycling and noticed that the same training-induced metabolites were released in humans.

Link: https://news.ki.se/study-shows-how-exercise-stalls-cancer-growth-through-the-immune-system