Can food really boost your immune system?

Food products that claim to boost or support the immune system are booming, from coffee and tea to cereals and snack bars. It’s no surprise, really. At a time of heightened concerns about infection and illness, we all want to reduce the risk of getting sick. But can specific foods help us do this? And are these products actually good for us Food companies certainly want us to think so.

The words used on packaging and websites suggest products confer health benefits, although exactly what those are is usually unclear. One mushroom-infused coffee, for example, claims to ‘boost health and immunity’, while a well-known breakfast cereal simply carries the words ‘immune support’ in large lettering on the box. There’s even a popular brand of tea bags called Plus Immunity.

Sometimes packaging or websites indirectly suggest the product confers a benefit. For example, a manufacturer of snack bars fortified with vitamin D asks on its website: Can vitamin D reduce the risk of Covid-19? Underneath is a link to a Queen Mary University of London study investigating whether taking high doses of vitamin D can protect against Covid-19. (Note: the study is ongoing and the results won’t be known until summer 2021.

Can you boost your immune system… and is it a good idea?

Messaging about immunity-boosting suggests these foods can somehow ramp up our defence system like a force field to destroy invading baddies. But it’s not that simple. The immune system is a complex web of connected processes involving the skin, lymph nodes, bone marrow, gut and other organs. Our ‘innate immune response’ is our frontline defence against foreign invaders (antigens), such as bacteria and viruses. It’s this response that produces mucus (to trap and flush them out) and triggers fever (to make it harder for them to multiply). After this our ‘acquired immune response’ (which recognises harmful elements and deploys a precise response acquired through illness/vaccines) takes over to attack and destroy the invaders. The idea of ‘boosting’ the immune system might sound appealing, but it wouldn’t necessarily be desirable and doesn’t make scientific sense, says registered nutritionist Kerry Torrens. People with autoimmune diseases and allergies, for example, have hyperactive immune systems that can damage rather than protect their bodies.

“What we do want to strive for is immune balance,” Torrens explains. “A useful analogy might be that you want the army to fight the invaders but then you need peacekeepers to resolve and calm the storm and minimise any further damage. What would be beneficial is to support our immune defences rather than provide rocket fuel to super-boost them.” There’s no magic bullet for providing this support, but eating a varied and nutritious diet is vital, especially one that encourages good microbes in our gut to flourish. That means consuming lots of fibre, a wide range of colourful fruit and vegetables and regular servings of fermented foods. “Our gut plays a big role in our immune health with 60–70% of our immune defences residing there,” Torrens says. “Experts suggest we aim for 30 different foods a week to do that. This isn’t as daunting as it sounds because eating a variety of different nuts, seeds, fruits, vegetables and wholegrains all counts.”

What about those health claims?

Under current food labelling laws, no product can directly make a health claim unless scientifically proven and authorised for use on packaging. Food companies are allowed to claim certain ingredients ‘contribute to the normal function of the immune system’. These include vitamins A, B12, B6, C and D along with zinc, copper, folate, iron and selenium. That’s why many products that mention immunity on the packet have some of these nutrients added. But Professor Charles Bangham, chair in Immunology at Imperial College London, says these products won’t help your immune system or your general health unless you’re deficient in key nutrients. “If you eat a normal balanced diet and you already have a sufficiency of these vitamins and trace elements, eating more of them will not boost your immune system any further,” Prof Bangham says. “A lot of food manufacturers are cashing in and exploiting people’s anxieties.”

What’s his advice to consumers faced with an array of products claiming to benefit their immune system? “Don’t be lured into buying things because they mention the immune system,” he says. “Even without making a claim on the package, it’s obviously implied if they mention it.”

Prof Bangham says it’s true that many people living in the UK are deficient in vitamin D – and this situation has been exacerbated this year by many people staying indoors more than usual, but this is best addressed by taking supplements in line with government recommendations. Adults (and children from the age of one) are advised to take 10 micrograms (400 IU) daily between October and early March. He stresses that taking vitamin D supplements after catching Covid-19 is is unlikely to reduce the severity of the symptoms. “You need to have a sufficiency of vitamin D for weeks or months before you catch the virus,” he says. “That’s what will set your immune system up to be in a good position to respond when you get infected.”

The bottom line

Your immune system is best supported by eating a varied and nutritious diet, including gut-friendly foods such as kimchi, sauerkraut and live yogurt. In line with government recommendations, it’s also a good idea to take a vitamin D supplement during the winter months. And remember that a healthy immune system doesn’t come in a packet.