Can you slow down the ageing of your immune system?
There is concrete evidence that lifestyle changes, in particular a Mediterranean diet combined with more physical activity, can meaningfully reduce the number of aged immune cells; probiotics and vitamin D also show measurable effects, though it remains unclear whether this actually leads to falling ill less often.
As we age, the number of T-cells that have never encountered a pathogen declines. These so-called naive T-cells are crucial for recognising new threats. At the same time, the ends of the DNA in those cells become shorter and low-grade inflammation in the body increases. This process is called immune ageing and has been described in multiple studies, though precise figures are hard to give because studies differed considerably in how they measured it.
One of the most concrete indications that this process can be slowed comes from the PREDIMED-Plus study. People with excess weight and metabolic syndrome who followed a Mediterranean diet combined with more physical activity and behavioural coaching had 3.32% fewer aged T-cells in their blood after one year. After three years that difference had grown to 6.74%. Whether this also applies to people without excess weight or metabolic syndrome was not examined in this research.
Probiotics show measurable improvements in two specific immune functions in studies with healthy older adults: white blood cells become better at taking up and destroying invaders, and the activity of natural killer cells, which can attack tumour cells, increases. Three to twelve weeks of supplementation was sufficient to see these effects. Whether this also means people actually fall ill less often has not been shown.
Vitamin supplementation, in particular vitamin D and vitamin E, improves immune function in older adults in a statistically measurable way, though the overall effect is small. Vitamin D lowered inflammation markers and increased immune cell activity; vitamin E had the largest measured effect on the cellular defences. How this translates into fewer infections or a longer life is unknown.
Studies in animals show that an antiparasitic drug can stimulate the thymus, the gland where new T-cells are produced, after it has been damaged. The thymus shrinks considerably with age. However, this has only been observed in mice; whether it works in people is entirely unknown. Evidence from population research in so-called Blue Zones also suggests that a diet rich in plant compounds, social connectedness and a diverse gut flora go hand in hand with less immune ageing, but cause and effect cannot be separated there.
This answer draws on multiple combined studies and controlled studies in people, supplemented by animal research and observational population research. The findings on lifestyle (Mediterranean diet plus physical activity) come from a well-designed study, but specifically in people with excess weight and metabolic syndrome. The probiotic and vitamin findings are drawn together from multiple smaller studies; the practical significance of the measured immune changes is in both cases still unclear. The animal research on the thymus is considered early-stage and has no confirmation in people. The researchers behind the Blue Zones analysis live in the area they studied themselves, which limits their independence.
What does ageing of your immune system mean for your health?
Your immune system ages in measurable ways: it responds less effectively to new threats and maintains a smouldering inflammation that is associated with cardiovascular disease, dementia and cancer. An active lifestyle is the best-supported way to slow that process.
Does your immune system weaken as you get older?
Your immune system demonstrably weakens with age, but eating healthily and exercising can reduce the smouldering inflammation that accompanies it. It is still too early to rely on drugs targeting senescent cells.
How does your immune system age and can a blood test measure that?
Your immune system ages in recognisable ways: exhausted immune cells and smouldering inflammation are clearly visible features. The markers on which a blood test would be based are already well described, though no such standardised test yet exists.
Does your immune system age at a different rate than your heart?
Yes, your immune system and heart age at measurably different rates, and an ageing immune system is more strongly linked to a longer life than the heart is. These are associations, not causal evidence, but that is still a reason to take both seriously.
Does exercise help your immune system as you get older?
Exercise helps older adults: it lowers mild inflammation in the blood and noticeably reduces the risk of physical frailty. How it works on the deeper ageing of the immune system remains an open question.
Does spending more time outdoors help your immune system as you get older?
Spending more time outdoors may support your immune system as you get older, mainly through improved vitamin D production, but whether this actually leads to less illness has not yet been conclusively demonstrated. How polluted the outdoor air is also matters: in areas with serious air pollution, being outside can in fact be detrimental.