As lockdown comes to an end, it is inevitable that our immune systems will be put to the test as we are exposed to Covid and other bugs and viruses again. With masks and social distancing now a “personal responsibility” rather than a rule, and scientists warning that Covid transmission will soar along with other illnesses such as flu, maintaining good immunity has never felt more important.

Our immune system is a complex biological network that protects our bodies from viruses and disease, but like all systems it weakens with age. Our immune cells become less effective at hunting down invaders and start to misfire, causing damage, which is why people over 70 are more vulnerable to viruses and diseases – a fact that was ruthlessly highlighted throughout the pandemic.

This decline in immunity happens to us all, but now scientists are discovering how our lifestyles can speed up or slow down the rate at which it does. Obesity, stress and behaviours such as smoking can raise your immune age, while healthy changes can turn back the clock and lower it, reducing our risk of serious illness and helping you live longer.

In other words, a 35-year-old can have the immune system of a 50-year-old, or a healthy 60-year-old could have that of a much younger adult.

“Our immune systems age just like the rest of us,” says Dr Jenna Macciochi, a leading expert in immunology at the University of Sussex and author of Immunity: The Science of Staying Well.

“However, recent studies have found that our ‘immune age’ isn’t necessarily the same as our chronological age.”

Covid-19 has shone a light on the importance of looking after our immune systems, but Dr Macciochi stresses: “Remember, immunity is for life, not just for the easing of restrictions or the pandemic overall. Long after all this is over, how well you take care of your immune system will determine how it – and you – will age.”

Regular exercise can give you the immunity of a 25-year-old

Studies show regular exercise in old age can prevent a decline of the immune system. One 2018 paper from King’s College London followed 125 long distance cyclists, some in their 80s, and found they had the immune systems of 20-somethings. “If exercise was a pill, everyone would be taking it,” said Prof Norman Lazarus, then 82, who took part in and co-authored the research.

Professor Janet Lord, another co-author, said while our immune system declines by 2-3 per cent a year from our 20s, older exercisers have extra protection from this decline, are protected more from viruses and will respond better to vaccines.

“Even a daily lunchtime walk will help,” says Dr Macciochi. “Moving every day is essential for your lymphatic system, which helps your immune cells perform more efficiently.”

Research in the British Medical Journal found those who walked for at least 20 minutes a day had 43 per cent fewer sick days due to the common cold.

Look after your muscles, too – strength training has been shown to have the effect of sheltering certain types of T-cells, important in our immune response.

Eat more protein

Evidence shows that poor gut health can increase immune age, says Dr Macciochi, while a healthy microbiome can slow down the ageing process.

“Aim to eat as many different plant foods as possible. I also have protein with every meal because this supports the antibodies needed by your immune system.” Slow fermented sourdough bread is good for gut diversity, as is seasonal fruit and vegetables, whole grains and legumes.

“When it comes to immunity, food and nutrients don’t work in isolation,” says nutritional therapist Amelia Freer. “It’s more important to look at overall dietary patterns, rather than focusing on individual foods.”

However, Freer agrees that protein is particularly important. According to a 2018 review on diet and immune ageing, adequate protein is important for effective immune responses. “With age, people tend to consume lower amounts of protein when, in fact, they may need more,” she says. “Protein doesn’t just have to mean meat or fish either. It can also include pulses, nuts, seeds, tofu, dairy and eggs.”

A study of 120 older adults found that a Mediterranean diet, high in vegetables, fruit, pulses, wholegrains, oily fish and olive oil, had a positive impact on ageing immune cells. “The Mediterranean diet also tends to emphasise oily fish, such as salmon, mackerel, sardines & trout – aim for a portion a week.”

A cold shower may stop you getting sick

Exposure to cold temperatures stresses the immune system in a beneficial way, creating an anti-ageing effect.

That doesn’t necessarily mean plunging into the wild swimming trend. A study in the journal PLoS One found people who take cold showers are 29 per cent less likely to call in sick for work. The study asked 3,018 people who usually take hot showers to turn the nozzle to cold for 30, 60 or 90 seconds. The researchers didn’t find a difference in benefits between a 30 or 90 second cold blast, leading them to conclude even short bursts of cold water triggers the body’s immune system. “At the end of every shower, turn the temperature to the coldest setting for 20 or 30 seconds,” advises Dr Macciochi.

Get outside – and take vitamin D

Vitamin D’s role in immunity is now well established. Experts agree that we should spend plenty of time outside and take supplements between October and March.

“I’m often asked about dietary supplements, but I don’t think they’re particularly helpful,” says Professor Charles Bangham, chair of immunology at Imperial College London. “One exception is vitamin D. Although direct evidence between vitamin D and protection from Covid-19 is lacking, there is reasonably strong evidence that people deficient in vitamin D are more likely to get respiratory infections. About a third of us are vitamin D deficient. Our main source is exposure to sunlight – most of us missed our summer holiday last year and may miss it again this year.”

Sleep, let go of resentment and see your friends

When we’re asleep, our immune system releases proteins called cytokines, which we need to fight infection or inflammation in the body or to cope with stress. A lack of sleep can decrease production of these cytokines, as well as infection-fighting antibodies. “Sleep is the bedrock of your immune system,” says Dr Macchiochi. “If you don’t sleep properly, other immune-protecting behaviours during the day like eating well and exercise won’t really count.”

Avoiding, or managing, stress and letting go of resentment is important too, she adds.

“There has been analysis suggesting that different personality types have different immune responses. If you’re quick to anger, your immune system is constantly primed for inflammation and will weaken more with age. Stress really dampens down our immune system, so find ways to manage it.” Be mindful of turning to alcohol to unwind. A 2014 study found that binge drinking (defined in the study as consuming up to five measures of spirits) reduced levels of white blood cells, which combat infections, making your immune system less active.

Turning to hobbies to relax – such as sport, music, art or cooking – is a better idea, and maintaining friendships too.

“Social connections have been found to be important in immune ageing,” says Dr Macciochi. “When we feel lonely, however, our immune systems go on high alert and an inflammatory response takes place.” So while a return to the office may feel daunting, it could actually give your immune system a boost.

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