Not just weight and strength: physical activity also changes the immune system

Physical activity does not affect only weight, physical fitness or muscle strength. It changes the way the body uses energy, controls inflammation and prepares the immune system to respond better to threats, as salute.eu writes.

A new study published in the journal Science Advances has analysed this effect at the molecular and cellular level, comparing 40 people who regularly engaged in physical activity with 46 sedentary people, part of a Chinese research group. The active people met the World Health Organization’s recommendations, with at least 150 minutes of moderate physical activity or 75 minutes of vigorous activity per week, spread over at least three sessions.

The sedentary group, by contrast, reported no structured physical activity and spent most of the day sitting.

Changes in metabolism

According to the study, physically active people had lower levels of glucose and triglycerides in their blood, while they had higher levels of HDL cholesterol, known as “good cholesterol”.

More in-depth analyses also showed an increase in metabolites linked to the oxidation of fatty acids, energy production and antioxidant systems.

This suggests that the bodies of active people are better adapted to use fats as a source of energy and to cope with the oxidative stress that accompanies metabolic activity.

Physical activity also affects immunity

Another important change was observed in the immune system. The researchers identified changes in gene expression and chromatin accessibility in several immune cells, including monocytes, B cells, cytotoxic T lymphocytes and “natural killer” cells.

These changes are linked to processes such as antigen presentation, communication between immune cells and the response to viruses and abnormal cells.

According to the data, physical activity does not seem simply to “activate” the immune system, but to make it more regulated and more efficient, favouring immune surveillance and limiting some processes linked to chronic inflammation.

The link with ageing and chronic diseases

Acute inflammation is an important protective mechanism of the body, while chronic low-grade inflammation is linked to a series of diseases and conditions that become more common with age, including diabetes, atherosclerosis and functional weakening.

In this context, the metabolic and immune changes linked to physical activity may help explain the known link between regular exercise and better long-term health.

However, the researchers stress that the results should be interpreted with care. The study was observational and did not directly prove that physical activity caused all the changes identified.

Activity was self-reported by the participants and was not measured with monitoring devices. Moreover, the sample was relatively small, young and healthy, so the results cannot automatically be generalised to older people, people with chronic diseases or other populations.

The study’s main value lies in the mechanism: regular physical activity is not only a way to burn calories, but it seems to leave a measurable “trace” in the metabolism, in the immune cells and in the way the body manages inflammation.