Over the past few decades, more and more evidence has been gathered that being physically active reduces our risk of developing malignancies and dying from them. And in the case of cancer in particular, some large-scale studies have already shown that people who exercise are much less likely to develop thirteen different types of cancer than those who lead sedentary lives. But the findings in this field seem to indicate an even greater benefit: they suggest that exercise not only prevents cancerous tumors but may even help defeat them.
One of the first pieces of evidence for this came from a review of research published last year by the American College of Sports Medicine. Its authors concluded that regular exercise, in addition to reducing the risk of developing some tumors by up to 69%, can improve the outcome of cancer treatments and prolong the lives of patients.
But while this work was able to identify a clear correlation between exercising and having a better response to cancer, it does not provide any explanation for the mechanism. In this sense, he only points out that physical activity reduces inflammation and makes the body less hospitable to malignant neoplasms, which leaves the central question unclear.
In search of a more precise answer, a group of scientists from the Karolinska Institute in Stockholm began to study the role of white blood cells. As part of the immune system, white blood cells play a key role in our defense against cancer by detecting, navigating, and often killing malignant cells. Researchers have known for some time that different types of immune cells tend to target different types of cancer. But little is known about whether and how exercise affects any of these immune cells.
For their study, which was published in October in the journal eLife, the Swedish scientists decided to learn more by inoculating mice with different types of cancer cells and letting some of the rodents run, while others remained sedentary. After several weeks, the researchers saw that some of the runners showed little evidence of tumor growth.
Even more interesting is that most of those mice had been inoculated with cancer cells, which are known to be particularly vulnerable to a specific type of immune cell known as T lymphocytes. Hence, the researchers suspected that perhaps exercise was having a problem. particular impact on them.
To find out, they chemically blocked T lymphocytes in tumor cell-bearing animals and let them run. After several weeks and despite being active, the animals showed significant tumor growth, suggesting that these cells must be a key part of how exercise helps prevent some cancers.
White blood cells play a key role in our defense against cancer
For further confirmation, the scientists isolated T lymphocytes from mice that had run and those that had not. They then injected one or the other into sedentary animals prone to cancer. In this way, they saw that those rodents that received immune cells from the runners fought the tumors markedly better than the animals that had received immune cells from inactive mice.
These results excited the researchers because they seem to show that the effect of exercise on T cells is intrinsic to them and is persistent; in other words, that exercise had lastingly changed cells.
But what did exercise do to T lymphocytes to make them more effective at fighting tumors? To explore that question, the researchers let some mice run until they were tired, while others were left inactive. They then took blood from both groups and, when analyzed, found that they were quite different at the molecular level. The runners’ blood contained many more substances related to food and metabolism, with especially high levels of lactate, which is produced in abundance by working muscles.
A correlation was identified between exercising and having a better response to cancer
Suspecting that it was perhaps lactate that was improving the performance of T lymphocytes, the scientists added it to the lymphocytes of mice grown in laboratory dishes and saw that these cells became more active when faced with cancer cells. .
Of course, this finding was made in mice; not in people, so in principle there is no certainty if it would work the same. It remains a mystery whether our T lymphocytes respond in the same way to exercise and, if so, how much exercise is required for that. But in a context where physical activity is known to improve overall health, the Swedish researchers’ finding is very promising.