Does your immune system really weaken as you get older?
Your immune system does indeed weaken as you get older, but how quickly that happens varies considerably from person to person. Lifestyle factors play a role in this, although little has yet been proven specifically for humans.
Yes, the immune system really does weaken as you get older. This phenomenon is called immunosenescence. Both T cells and B cells (the two types of white blood cells that fight infections) become less effective. The innate immune system, the body's first line of defence, also deteriorates. The practical consequence: older people get infections more often, become more seriously ill from them, and respond less well to vaccines.
An additional mechanism is at play in T cells. The thymus, the organ where T cells mature, shrinks considerably with age. As a result, fewer new, fresh T cells are produced. The T cells that remain also lose diversity: they can recognise fewer different invaders. At the same time, the energy-producing structures inside the cells (the mitochondria) become damaged. This contributes to a higher risk of infections and cancer, as well as autoimmune reactions in which the body attacks itself.
There is a paradox in immune ageing. The immune defence weakens against infections, yet at the same time a chronic, smouldering inflammation develops that never fully subsides. Researchers call this 'inflammaging'. This persistent low-grade inflammation is associated with age-related conditions such as dementia, joint complaints, and type 2 diabetes. An inflammatory substance that plays a role in this also disrupts energy metabolism in certain brain cells of mice; in mice, blocking this substance restored both immune function and memory. Whether the same holds true in humans is unknown.
Not everyone ages immunologically at the same rate. In a study that followed 135 healthy adults for nine years, biological immune age turned out to be a better predictor of death than ordinary chronological age. Two people of the same age can therefore have very different immune conditions. What causes these individual differences has not yet been fully clarified, but lifestyle plays a role. For example, eating less (caloric restriction) slowed immune ageing in rats and reduced chronic inflammation. Whether this works equally strongly in humans has not yet been demonstrated.
Findings are based on multiple large review studies and mechanistic research. The decline in T cell and B cell function and inflammaging are broadly documented. Individual variation in immune ageing is based on one study with 135 participants (associational). Caloric restriction and the PGE2 mechanism are animal research and have not yet been translated to humans.