Why your immune system ages at 40 and 60 (and what to do about it)

The Duke University researchers mainly saw differences in the behaviour of a type of white blood cell called T-cells at ages 40 and 60, and in the genes which underpin them. T-cells support the body’s response to invaders like viruses and can kill cancerous or virus-infected cells. Whether they are behaving as they should has an impact on how well we age – if your body’s immune defences are lower, then you will be more vulnerable to infections, which is what happens to many older people, and particularly to men.

“We saw during the Covid pandemic that older people were much more at risk because their immune system is much less able to fight off the disease,” says Steves. “But it’s not just Covid. From national GP records, we see that when people reach their 70s and 80s, there’s an explosion in the numbers of infections – everything from urinary tract infections (UTIs) to chest infections. That’s because of changes in our immune system, in particular changes in T-cells.” Crucially, though, this isn’t the case for everyone. “In most people, T-cells become less prevalent and less numerous. But in some people they don’t, and if your T-cell immunity and T-cell function remain good in later age, that seems to be a potential resilience factor.”

At the same time, older women often have what the researchers called a “chronically activated” immune system, making them more susceptible to certain age-related diseases, autoimmune disorders and later-life allergies. Working out why this happens and how to boost resilience in people whose immune systems seem to be ageing faster, while also understanding why women’s immune systems are comparatively hyperactive, are key parts of helping more people have healthier later lives. The study researchers hope their work will contribute to more personalised treatments for immune-system or age-related disorders.

We may soon be able to test blood for ageing biomarkers, but we are not there yet, says Steves. “If you have symptoms which are worrying you, the advice is always to go to your GP. In our 40s and in our 50s, the risk of many diseases goes up, but the other benefit of seeing a GP at that age is you may get your blood pressure or cholesterol checked. We know that if we manage those risks well in midlife, we can reduce later-life risks.”

Looking after your immune system doesn’t have to mean buying expensive supplements, says Steves. “Regular physical exercise is one of the best ways of boosting your immune system and this has been carefully scientifically proven. Relative calorie restriction may also help – not eating too much is also evidence-based.” What should people in their 40s eat? “Well-replicated studies show that the Mediterranean diet – a diet that is high in wholegrains, fish, olive oil and plenty of fruit and vegetables, and low in processed food and meat – seems to improve immune function.”

As yet, there isn’t much data on whether men and women should be eating or exercising differently from each other for their immune health, says Steves. “We should have sex-specific advice. We don’t have good evidence, but we really should be generating it.”

“This paper really shows that midlife is different from older age. The advice I give patients who are on their way to becoming frail is different from the advice we give to younger age groups.” Steves notes that many older adults don’t consume enough protein or calories, so calorie restriction isn’t a good idea for them. “It’s harder for older adults to maintain muscle mass and that may be partly to do with immune system changes. If you’re starting to get even little tiny drops in weight, then that’s a signal to bump up the protein and calories in your diet.”

Exercise is key for 60-year-olds, too. “One of my favourite studies is the Master Cyclist study,” says Steves. This study showed that a mixed group of 125 amateur long-distance cyclists aged 55 to 79 had immune systems and T-cell activity comparable to those found in adults of around 20 (and much better than those in a control group of similarly aged sedentary adults). This suggests that ageing is not always about inevitable physical decline and may be partly driven by inactivity. “We can really change the immune system by doing regular exercise,” says Steves.

Vaccinations are another crucial anti-ageing trick if you’re over 65 or over 60 with any other comorbidities. “Multiple studies have now shown broader health benefits to having vaccinations,” says Steves.

“This is partly because every time people get flu or Covid, it has a knock-on effect on other organ systems and they are conditions which come with inflammation that can cause all kinds of medical problems. But we also think that the vaccination itself is actually ticking up the immune system, making it more resilient, and that might have longer-term effects not just for general ageing, but also reducing the risk of cardiac disease and even dementia.”

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