How exercise strengthens our immune system

Endurance training makes natural killer cells more efficient and effective against inflammation

Exercise not only trains our muscles and endurance – our immune system also becomes fitter, as a study has now confirmed. According to this study, regular jogging, cycling, and other endurance sports also "train" the natural killer cells of our immune system. In trained people, these white blood cells release more anti-inflammatory messengers, use cellular energy more efficiently, and respond more appropriately to pathogens and inflammation. This also applies to aging.

Endurance training not only strengthens muscles and stamina – our immune system also benefits.

Our immune system uses an entire arsenal of defense cells to protect us from disease. Natural killer cells (NK cells) are at the forefront. Unlike the more well-known T killer cells, they belong to the innate immune system and therefore don't need to first get to know their "enemies." They use recognition features already anchored in our genome to recognize and destroy cancer cells and virus-infected body cells.

Trained and untrained immune systems put to the test

It is now evident that exercise can make these immune cells fitter. Luciele Minuzzi of the University of São Paulo and her colleagues discovered this in a comparative study with older adults. "In a previous study, we found that obesity and a sedentary lifestyle can trigger an aging process of immune cells. This led us to investigate the other side: whether older people who have been doing endurance training for over 20 years have a better-prepared immune system," explains Minuzzi.

For their study, the researchers compared the responses of natural killer cells in trained and untrained men with an average age in their early 60s. As a further test, they exposed these immune cells to the inhibitors rapamycin and propranolol, which inhibit the function and proliferation of killer cells.

More efficient, more effective killer cells

The results showed that the immune cells of the physically trained test subjects responded more effectively to immune activation. They fought inflammation more effectively and released more anti-inflammatory messenger substances. "In these individuals, the NK cells functioned better during an inflammatory challenge and used energy more efficiently. One could say that training also 'trains' the immune system," says Minuzzi.

Unlike T cells, natural killer cells (NK cells) are part of the innate immune system. © NIAID

Similar results were observed with the use of the two inhibitors: "In both cases, even when the signaling pathways were blocked, the NK cells of the trained elderly individuals were able to maintain their immune function, while the cells of the untrained individuals showed signs of cellular exhaustion or a loss of the inflammatory response," reports Minuzzi. "This means that long-term endurance training is associated with protective 'immunometabolic' adaptations of NK cells in old age."

Exercise is important even in old age

According to the researchers, this demonstrates that exercise also has a positive effect on our immune system. Other factors such as nutrition, sleep, and stress also play an important role. "Physical exercise, however, is one of the factors that can positively influence the immune system," the team says. "Trained older adults exhibit more efficient and adaptable immunity, with better metabolic control and a lower propensity for cellular exhaustion."

(Scientific Reports, 2025; doi: 10.1038/s41598-025-06057-y)

Source: Fundação de Amparo à Pesquisa do Estado de São Paulo