Fighting fit: immune system mythbusting

Patsy Westcott / 19 January 2021

Sales of ‘immune-boosting’ supplements have soared. We separate the truths from the myths.



It sounds easy, doesn’t it: take this supplement or eat more of a particular food and you’ll boost your immune system. We’ve all become armchair immunologists in the past year as we seize on the latest headline or advice to try to reduce our risk of Covid-19.

But experts say the truth is more complicated. The immune system is a complex network of cells, tissues and organs that protects us from invaders but also repairs tissues and removes damaged cells.

As we age, so too does our immune system. ‘It’s a gradual slide rather than a cliff edge,’ says researcher Dr Natalie Riddell, from the University of Surrey. ‘As we get older our cells become more inflamed, sometimes called inflammaging.’ This puts a strain on the highly specific adaptive part of our immune system that remembers the threats we’ve been exposed to in the past, causing it to decline.

'I would caution against “experts” who tout quick fixes. There is no such thing.'

It’s why the over-70s are more vulnerable to colds and flu, as well as Covid-19, says immunologist Dr Jenna Macciochi, author of Immunity: The Science of Staying Well. It’s also why latent viruses, such as shingles caused by the chickenpox virus, can reactivate in later life. And it explains why we have a weaker response to vaccinations after age 65.

Recently, scientists have homed in on a process called autophagy as a major culprit in immune ageing. Autophagy removes debris in all our cells, including immune cells, but declines as we age. ‘In autophagy the unwanted material is picked up and shunted off for recycling and reuse, a bit like a rubbish truck taking waste to the incinerator or recycling plant,’ says Oxford University professor Katja Simon, who is investigating the role of autophagy in immunity and how to kick it back into action.

As for ‘boosting’ immunity, it’s not quite that simple, explains Dr Macciochi. ‘I would caution against “experts” who tout anything immune-boosting, especially quick fixes. There is no such thing. The immune system is shaped by things we can’t control, such as age and genetics, but also by things we can, like a balanced diet, adequate sleep and exercise. That’s what we need to focus on.’

Read our guide to the Covid-19 vaccination

Immune system mythbusting

Sitting down is bad for immunity

TRUE. ‘A sedentary lifestyle, obesity and loss of muscle mass can accelerate immune decline, as can smoking,’ says Dr Macciochi. ‘Lifestyle changes, such as staying active, eating a healthy diet and taking care of your gut microbiome, can help reduce it.’ Up to 80% of the immune system resides in your gut, so encourage diversity of gut bacteria by eating different coloured fruits and veg to provide a wide range of plant chemicals and fibre (30g a day). Fermented foods, such as mould-ripened cheeses, live yogurt and the ‘3 Ks’ (kimchi, kombucha and kefir), are a good addition.

Fasting can rejuvenate the immune system

TRUE. ‘There’s evidence that fasting – through calorie restriction or intermittent fasting – improves autophagy and cell recycling. It can also increase immune cell production,’ says Professor Simon. Fasting lowers the number of white blood cells, a key component of the immune system. This seems to switch on the production of new cells when you begin eating again.

Lemons boost your immune system

FALSE. No one food or nutrient boosts immunity. However, certain polyphenols (plant compounds found in fruit and vegetables) are known to improve autophagy and so rejuvenate the immune system. The key ones are: quercetin, found in onions and apples; epigallocatechin gallate, found in green tea; curcumins, found in turmeric; and resveratrol, found in red grapes and red wine. It’s not known how many polyphenols are needed for this effect. You can’t just eat ten apples in the hope of improving immunity. Experts recommend eating 30 different fruits, veg, nuts and seeds a week.

Taking supplements is the answer

FALSE. ‘There’s little benefit from taking more than you need,’ says Dr Macciochi. However, there are exceptions, including vitamin D, omega-3, and – for vegans – vitamin B12. Zinc helps limit the duration and symptoms of upper respiratory infections, according to Dr Macciochi although she cautions against taking it long-term as it can interfere with the absorption of other nutrients. Findings from the Zoe Covid Symptom Study, meanwhile, suggest that multivitamins, vitamin D, omega-3 and probiotic supplements may have a small protective effect but vitamin C, garlic and zinc had no effect.

Mushrooms and mature cheese might help

TRUE. Research is at an early stage, but Professor Simon is studying the effects of a natural compound, spermidine, found in aged cheeses (such as Parmesan, brie and mature cheddar), mushrooms, fermented soya products, legumes, corn and whole grains. Spermidine mimics calorie restriction and turns on autophagy. The result appears to be an improvement in the function of immune cells.

A good social life improves immunity

TRUE. ‘In studies of carers, stress levels and suppression of the immune response are linked to the amount of social support they report,’ says Dr Riddell. The reason? Two stress hormones, adrenaline and cortisol, are key regulators of the immune system and especially of the T cells at the heart of the body’s immune response. Disruptions in the rhythm of the release of these hormones as a result of stress can have profound effects on T cell immunity, especially as we get older.

Too much exercise reduces immunity

FALSE. ‘Most people don’t do enough exercise,’ says Olympian Greg Whyte OBE, professor in applied sport and exercise science at Liverpool John Moores University. Exercise can help strengthen immunity, he points out. ‘We see lower rates of upper respiratory tract infections in physically active people, which supports its role in immune health.’ Immune specific guidelines don’t exist, says Professor Whyte. But 150-300 minutes of moderate intensity physical activity, such as brisk walking, or 75-150 minutes of vigorous intensity aerobic exercise, such as running or HIIT, plus two or three strength sessions a week could help prime immunity.

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