Does your immune system age at a different rate than your heart?
Your immune system and heart do indeed age at a different pace and through different mechanisms, although they do influence each other. If you want to know how quickly your immune system is ageing biologically, factors such as chronic stress and sex are at least as relevant as your cardiac risk factors.
Immune cells age faster than your calendar age would suggest, and they do so in a completely different way from the heart. T cells change in character: they are no longer fresh and ready to tackle new threats, but are instead specialised in pathogens you have encountered before. The variety of disease-causing agents they can still recognise shrinks. B cells produce a less diverse range of antibodies. These are recognisable patterns of immune ageing that have nothing to do with the rate at which your heart muscle or blood vessels grow older.
Moreover, the immune system increasingly works against itself as you age. It settles into a smouldering state of chronic low-grade inflammation, known as 'inflamm-aging'. Researchers do not regard this as a side effect of ageing but as a driver of it. That smouldering inflammation is therefore the 'first hit' in a model in which organ-specific diseases such as cardiovascular disease or dementia only occur when an unfavourable genetic predisposition -- the 'second hit' -- is added on top.
How quickly your immune system ages also varies from person to person and is linked to factors that have nothing to do with heart health. Chronic stress accelerates the molecular ageing of immune cells: women with the highest stress burden had immune cells that appeared molecularly around ten years older than those of low-stress women. Sex also plays a role: in men, the immune system appears to age more quickly than in women, although that gap narrows after menopause. The heart follows a completely different pace, driven by different risk factors.
Yet the immune system and the heart are not independent of each other. Capillary macrophages -- immune cells that help repair small blood vessels -- disappear more rapidly with age than the capillaries themselves decline. This was observed in both mice and humans. The capillaries are therefore repaired less effectively, which promotes vascular ageing. Here, immune ageing and cardiovascular ageing concretely intersect.
All claims are based on associational or probably causal evidence of moderate strength; no large RCTs. The finding on stress and telomeres concerns women only. Animal studies (mice) have been supplemented with human observations, but experimental evidence in humans is limited.