Does your immune system really weaken as you age, and is there anything you can do about it?

Yes, the immune system weakens with age, and this is well documented. Scientists call this 'immunosenescence': far-reaching changes in both the innate and adaptive immune defences that together increase the risk of serious infections, cancer, dementia and cardiovascular disease. One of the central causes is the shrinking of the thymus, the organ where T-cells mature. As a result, fewer new, naive T-cells are produced, while the proportion of 'memory' cells grows in a disproportionate way. Natural killer cells, which clear out tumours and infected cells, become less effective over the years, even as their numbers actually increase. And a specific group of B-cells (the cells that produce antibodies) expands with age in a way that suppresses the generation of new, fresh B-cells.

Alongside this weakening, a second equally important process is at work: inflammaging. This is a smouldering, low-grade inflammation present throughout the body, even in the absence of any visible infection or disease. It is not merely a side effect of immunosenescence, but is regarded as an independent risk factor for virtually all major age-related diseases. Changes in the gut microbiome are mentioned as a possible driving factor, although that relationship has not been sufficiently studied to draw firm conclusions.

Immune ageing is not a uniform process that affects everyone at the same age. Measurements using so-called immune-ageing clocks at the cellular level reveal large individual differences: two people of the same chronological age can have markedly different biological immune ages. Centenarians even demonstrate that immunosenescence does not necessarily have to lead to serious disease: they appear to be better able to adapt their immune systems to the demands of very old age, although observational research of this kind does not tell us precisely what protects them. Sex differences also play a role: men and women do not age immunologically in the same way, which translates into different susceptibilities to age-related conditions.

Evidence on what you can do yourself is currently limited and in part still purely exploratory. Senotherapeutics, agents that target senescent cells or inhibit their harmful secretions, are being investigated as a potential intervention, but there are as yet no clinical studies in humans demonstrating that these agents are safe and effective. On the subject of vaccination, research with BCG vaccinations showed signs of immunological rejuvenation in a specific type of T-cell in some individuals. This was an early, exploratory finding and not proof that vaccination structurally rejuvenates the immune system. The same research does suggest, however, that serious infections such as COVID-19 can temporarily increase the biological age of the immune system, although that effect diminished after recovery. At present, therefore, there is no proven, directly applicable intervention with which people can reverse or halt their immune ageing.