Professor Luigi Fontana

Elevated insulin has long been linked to obesity and type 2 diabetes. Now scientists show it may also age the immune system itself, increasing inflammation, weakening infection defence, and shortening lifespan.

Ageing is often described as an unavoidable consequence of time. But growing evidence suggests it is also shaped by the signals circulating in our blood. A new study published in Science Immunology points to an unexpected culprit: insulin.

Insulin: More than a blood sugar hormone

Insulin is best known for moving sugar into cells after meals. But when insulin stays high—often with belly fat—it is linked to diabetes, heart disease, cancer, and faster aging in organs like the liver and brain. Until recently, scientists didn’t know how insulin might affect the immune system.

Meet the immune cells involved: B cells

B cells are a type of white blood cell that help protect us from infections. They recognise invading germs and make antibodies that can block or tag them for removal. In a healthy immune system, B cells stay mostly quiet, switching on only when needed and switching off once the threat passes.

What changes with age

New research published in Nature Immunology shows that B cells change as we age. Instead of responding mainly to infections, older B cells begin responding to insulin. When insulin stays high, these cells remain switched on even without infection.

Why constant immune activation is harmful

When B cells stay overactive, they constantly stimulate other immune cells, especially CD4 T cells. Over time, this wears the immune system down. Fewer fresh immune cells are made, exhausted cells build up, and protection against new infections weakens. Ongoing inflammation then damages tissues, promotes scarring, and increases chronic disease risk.

A remarkable finding on lifespan

The most striking result came when researchers reduced insulin signalling only in B cells, without removing the cells. The mice lived much longer: median lifespan rose by about 36 percent, and some lived beyond three years, unusually old for mice. They were healthier too, with less frailty, lower inflammation, and better metabolism.

What this tells us about ageing

The study suggests insulin links metabolism to immune ageing. When insulin stays high, B cells act like sensors of excess energy, turning overeating, inactivity, and visceral fat into ongoing immune activation. This speeds immune ageing and can drive whole-body decline. Simply put: high insulin may age immunity faster.

The bigger picture

Excess visceral fat promotes inflammation and lowers adiponectin, a hormone that helps the body respond to insulin. This makes cells insulin resistant, so the body produces more insulin to cope. Over time, persistently high insulin may drive ageing itself – not only in metabolic organs, but also in the immune system.

The encourageing message is that insulin levels respond strongly to lifestyle

The most effective ways to lower insulin and improve insulin resistance include reducing deep belly fat and increasing muscle mass. Regular movement matters, but structured exercise helps most – combining strength training with aerobic activity to improve how the body uses fuel.

Food choices matter too

Eating fewer highly processed foods and more high-fibre whole foods – vegetables, whole grains, legumes, nuts, seeds, and fruit – can reduce insulin spikes and improve long-term insulin levels. These steps do more than control blood sugar: they may help slow immune ageing, reduce inflammation, and support healthier ageing overall.

Not written in our genes

Ageing is not only written in our genes. It is shaped by daily biological signals, including insulin. By understanding how metabolism and immunity interact, we may uncover powerful ways to extend not just lifespan, but years lived in good health.