Exercise is well known for strengthening muscles, lungs, and the heart, but new research shows it also “trains” the immune system.
An international team of scientists has found that older adults who have been doing endurance sports for decades have immune cells that are stronger, more adaptable, and less likely to trigger harmful inflammation.
The study, published in Scientific Reports, looked closely at natural killer (NK) cells.
These white blood cells are part of the body’s first line of defense, hunting down virus-infected cells and even cancer cells.
Researchers compared the NK cells of nine older adults, average age 64, who were divided into two groups: those who had been doing endurance training such as long-distance running, cycling, or swimming for more than 20 years, and those who had not trained.
In past studies, the same group of researchers found that obesity and a sedentary lifestyle can cause immune cells to age prematurely.
That led them to ask the opposite question: could years of endurance training keep immune cells young? The answer, they discovered, was yes.
In trained older adults, NK cells functioned much better when faced with inflammatory challenges. Their cells used energy more efficiently, responded more effectively, and showed fewer signs of exhaustion.
“It’s as if exercise not only strengthens the body but also trains the immune system,” explained Luciele Minuzzi, lead author and a visiting researcher at Justus Liebig University in Germany.
The trained participants’ NK cells also showed fewer inflammatory markers and more anti-inflammatory markers compared to untrained peers.
This means their bodies had greater control over inflammation, an important finding because uncontrolled inflammation is linked to many age-related diseases, including heart disease, diabetes, and cancer.
To test how these cells worked under stress, researchers exposed NK cells to drugs such as propranolol, which blocks adrenaline-related pathways, and rapamycin, which interferes with cell growth signals.
Even when these key pathways were blocked, the NK cells of trained older adults maintained their function, while those of untrained adults quickly showed fatigue and failure. The results suggest that decades of exercise cause “immunometabolic” adaptations—changes that make the cells more efficient and resilient.
The researchers also compared older master athletes with younger athletes in another study.
They found that younger athletes had a stronger inflammatory response after exercise, producing more inflammatory molecules such as IL-6 and TNF-α. By contrast, the older athletes’ immune systems responded in a more controlled and balanced way.
The scientists believe this shows that long-term exercise teaches the immune system how to react appropriately—strong enough to fight threats, but not so exaggerated that it causes harm.
According to Professor Fábio Lira, who coordinated the project at São Paulo State University in Brazil, these findings underline the importance of regular exercise as a factor influencing immune health, alongside sleep, diet, stress, and medications. By keeping inflammation in check, long-term endurance training may help prevent many chronic diseases associated with aging.
The takeaway is clear: just as the body gets stronger with exercise, the immune system does too.
Over the years, consistent physical activity seems to “educate” immune cells to react with precision and control, avoiding the damaging effects of excessive inflammation. This kind of training may be one of the keys to healthier aging and a lower risk of disease later in life.
If you care about health, please read studies that vitamin D can help reduce inflammation, and vitamin K could lower your heart disease risk by a third.
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