For many years, doctors and scientists have known that regular physical activity helps people stay healthy. Exercise can strengthen the heart, improve muscle power, and help control weight. It can also reduce the risk of diseases such as diabetes and heart disease.
However, scientists are now discovering that the benefits of exercise go even deeper. A new study shows that long‑term endurance exercise may also improve how the immune system works, especially in older adults.
The research was carried out by an international group of scientists and was funded by the São Paulo Research Foundation (FAPESP). The results were published in the scientific journal Scientific Reports. The study focused on a special type of immune cell called a natural killer cell, often shortened to NK cell.
These cells are an important part of the body’s defense system. They patrol the body looking for infected cells, damaged cells, or cells that have turned cancerous. When they detect a problem, they attack and destroy the harmful cells before they can spread.
Natural killer cells belong to a group of white blood cells called lymphocytes. They are part of the body’s first line of defense against viruses and other threats. Unlike some other immune cells that need time to recognize a specific pathogen, NK cells can react quickly. Because of this rapid response, they play a crucial role in keeping the body healthy.
As people grow older, the immune system often becomes weaker and less efficient. Scientists sometimes refer to this process as immune aging.
Older adults may experience more inflammation in the body and may have immune cells that do not respond as well to infections or abnormal cells. Previous research has shown that obesity and a sedentary lifestyle can make this process worse by causing immune cells to age faster.
Because of this, researchers wanted to explore the opposite situation. They asked an important question: if inactivity can weaken the immune system, could many years of regular exercise make it stronger? To answer this question, scientists examined older adults who had spent decades practicing endurance exercise.
Endurance exercise refers to activities that keep the body moving for long periods of time. Examples include long‑distance running, cycling, swimming, rowing, and even brisk walking. These activities challenge the heart, lungs, and muscles to work steadily over time.
In the study, scientists collected immune cell samples from nine participants whose average age was about 64. The group was divided into two sets. One group consisted of individuals who had practiced endurance exercise regularly for many years. The other group included people of similar age who did not have a history of long‑term training.
When the researchers examined the natural killer cells from both groups, they discovered clear differences. The NK cells from people who had trained for many years were more adaptable and functioned more efficiently. These cells were also better at managing inflammation, which is the body’s natural response to injury or infection.
Inflammation can be helpful in small amounts because it helps the body fight disease. However, too much inflammation over a long period can damage tissues and contribute to many health problems, including heart disease, diabetes, and certain cancers. In older adults especially, uncontrolled inflammation can become a serious issue.
The scientists found that NK cells from trained individuals had fewer markers linked to inflammation and more markers associated with anti‑inflammatory activity. In simple terms, the immune systems of these active older adults appeared to be better balanced. Their immune cells could respond when needed but were less likely to overreact.
The researchers also looked at how these immune cells produced and used energy. Cells need energy to perform their tasks, and immune cells must quickly generate energy when they encounter a threat. The study showed that NK cells from trained individuals used energy more efficiently than those from sedentary participants.
To better understand how these cells behaved, the scientists exposed them to certain laboratory drugs that affect cellular pathways.
One of these drugs was propranolol, which blocks the adrenergic signaling system related to stress hormones such as adrenaline. Another drug was rapamycin, which blocks a pathway known as mTORC1 that controls cell growth and metabolism.
Even when these pathways were blocked, NK cells from the trained older adults continued to function relatively well. In contrast, the NK cells from sedentary individuals showed signs of exhaustion and reduced ability to respond to inflammatory challenges. This suggests that long‑term exercise may help immune cells become more resilient and adaptable.
In another related study, the same research group compared immune responses between young athletes and older athletes who had trained for decades. The researchers studied blood samples from 12 master athletes with an average age of 52 and compared them with younger athletes whose average age was about 22.
When scientists exposed these blood samples to a substance that mimics infection, both groups produced molecules that signal inflammation. One of these molecules was IL‑6, which helps coordinate the immune response.
However, the increase in IL‑6 was much stronger in the younger athletes. Another inflammatory molecule called TNF‑alpha increased only in the younger group.
These results suggest that older athletes who have trained for many years develop a more controlled immune response. Their bodies still react to threats, but the response is more balanced and less extreme. Researchers believe that decades of physical training may “teach” the immune system how to respond more efficiently.
The lead researcher Luciele Minuzzi, who conducted part of the work at Justus Liebig University Giessen in Germany, explained that long‑term exercise seems to train the immune system in a similar way that it trains muscles. Over time, the body becomes better prepared to deal with inflammatory challenges and other stressors.
These findings are important for understanding healthy aging. Many age‑related diseases are linked to chronic inflammation and poor immune regulation. If regular exercise can help maintain a more balanced immune response, it may reduce the risk of these conditions and improve overall health later in life.
However, the researchers also emphasize that immune health depends on many factors. Sleep quality, nutrition, vaccination, stress levels, and certain medications can all influence how well the immune system works. Exercise is just one piece of a complex puzzle, although it appears to be a very important one.
Overall, the study suggests that decades of endurance training can produce lasting changes in immune cells, helping them function more effectively and respond to challenges in a controlled way. While the study involved a relatively small number of participants, its detailed analysis of immune cell behavior provides valuable insights.
Future research with larger groups of participants will help confirm these findings and clarify exactly how exercise reshapes the immune system over time. Even so, the results add to growing evidence that staying physically active throughout life may be one of the most powerful ways to support healthy aging and maintain a strong immune system.
If you care about cancer risk, please read studies that exercise may stop cancer in its tracks, and vitamin D can cut cancer death risk.
For more health information, please see recent studies that yogurt and high-fiber diet may cut lung cancer risk, and results showing that new cancer treatment may reawaken the immune system.
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