The evidence consistently indicates that regular, moderate physical exercise helps reduce the chronic low-grade inflammation that accompanies ageing and thereby supports the immune system. This is plausibly causal, but has not yet been precisely quantified in large randomised trials. In practical terms, consistency and moderate intensity are the key words; those who suddenly begin training very hard risk a temporary dip in their immune defences.
Regular exercise helps the immune system in later life in a concrete way: it suppresses the smouldering, chronic low-grade inflammation that is characteristic of ageing and that the scientific literature calls 'inflammaging'. This persistent inflammation raises the risk of age-related conditions, functional decline and premature death. Exercise is considered one of the few non-pharmacological strategies capable of countering it, with relatively few side effects1.
The effect of exercise on the immune system is not black and white. Regular, moderate training has an anti-inflammatory effect and lowers the risk of chronic metabolic and cardiopulmonary diseases through favourable changes in immune cells (leukocytes), red blood cells and signalling molecules (cytokines). Heavy, intensive exertion tells a different story: after a major strength effort or an exhausting competition, a temporary dip in immune defences occurs, leaving the body briefly more susceptible to infections. This effect is reversible, but it is something to bear in mind for older adults who suddenly take up very intensive exercise2,3.
A less well-known mechanism runs through the mitochondria, the energy factories of the cell. Exercise activates mitophagy: the process by which damaged mitochondria are cleared away and replaced by healthier ones. Reduced mitophagy is associated with age-related diseases and weakened immune function. Exercise keeps this self-cleaning system active. The precise magnitude of this effect in older people has not yet been quantified4.
There is also a striking, though still early, finding concerning exercise, gut bacteria and cancer immunity. In cell culture and mouse studies of melanoma, exercise was shown to stimulate the production of the substance formate via the gut microbiome. Formate enhances the activity of CD8 T-cells, immune cells that attack cancer cells, and made immunotherapy (checkpoint inhibitors) more effective. In humans, formate has so far only been identified as a potential signalling molecule (biomarker), not as a proven therapeutic agent. This research is still at an early stage and has not yet been translated into a recommendation for older people5.
Finally, exercise has been linked to changes in kynurenine metabolism, a metabolic pathway that plays a role in energy production and immune regulation. Whether this yields concrete immune benefits in older adults cannot be established on the basis of the available studies; this is an association, not a demonstrated effect6.
Based on multiple human and preclinical studies (PMID 38052484, 32342473, 10893431, 38036770, 40639377, 30980044, 36356628). The overall quality of evidence for the anti-inflammatory effect of regular exercise is moderate; the mechanistic findings (mitophagy, formate, kynurenine) are largely preclinical or limited to small human studies. No randomised controlled trials or meta-analyses were available as direct sources.