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Food and immune function. Can you eat your way out of COVID19?

Updated: Apr 16, 2022

COVID19 is one of the latest marketing opportunities. Influencers and companies are selling products that claim to help to fight off the virus, or they’re spreading misinformation about the role of food and supplements. But is there any truth in some of these claims? Are there any foods or supplements that we should be stocking up on in the next few weeks?

Supplement companies have been using specific nutrients to sell products that boost your immune system or support normal immune function for many years. So taking a supplement to keep our odds of getting the virus or related symptoms seems like a no-brainer, right?

Well, unfortunately the idea that specific nutrients, foods or supplements can boost our immune function is backed by little to no scientific evidence. Our immune systems are more complex than that.

In a nutshell, our immune system is made up of many tissues and organs. It uses two main lines of defence: innate and adaptive. Both are different but equally important:

  • The innate immune system is our first line defence (skin and mucus membranes found around internal organs), which is able to rapidly identify and destroy infections.

  • The adaptive immune system works over time to adapt or learn about an infection to respond appropriately and It will remember it for future reference (works more specifically than our innate defence).

Then our immune function is influenced right from birth. For example, babies delivered by cesarean birth (or c section) may have an impaired immune system later on in life compared to those delivered vaginally.

This is further influenced by our exposure to microbes; aka how dirty or clean we or our parents are. Contrary to belief, being a little bit less clean may actually help build a healthy immune system. So being too clean, particularly in infancy, can be negative for our immune function (coined the "hygiene hypothesis").

Simply consuming a vitamin C supplement will not drastically alter our immune function over night. Building up our immune system takes time, so the idea that we can boost our immune system is simply wrong. Plus, we actually don’t want a boost in our immunity. For example, autoimmune conditions such as coeliac disease are characterised by a heightened immune system.

However, don't give up yet as there is some hope (and evidence) that what we eat and our lifestyles can help protect our immune system. Lets discuss the evidence around diet:

Calories (kcal) or energy

If we’re cutting down on calories for whatever reason, then it will be harder for us to meet all of our nutritional needs. Particularly if we’re cutting out food groups (think gluten-free, vegan, keto). This may lead to deficiencies which can impair our normal bodily functions; including our immune function.

Research shows that the body's immune response is poor when nutrition is compromised. Fad diets such as that juice detox (shudder) or that water fast (crying) will increase our risk of deficiencies and may reduce our immune response.

Bare in mind that everyone has different calorie or energy needs (especially if you are being more or less active). We can assess whether we are eating the right amount by weighing ourselves (no more than monthly) or considering how our clothes fit, as this will indicate if we are eating enough calories. Overtime, if our weight goes down then we are in a deficit; if it goes up then we are in a surplus; if it stays the same we are at a balance.


Around 70% of our immune system is located in our gut, otherwise termed the gut-associated lymphoid tissue. One of the roles of our gut is to maintain a healthy balance of cells, optimising our ability to fight off diseases and infections. Within the gut lies trillions of different microorganisms otherwise coined the gut microbiota. One of their many roles is to defend your body from diseases and illness.

The fibre we consume in our diet, makes its way down our digestive tract and into our large intestine where it is processed by gut microbiota. The gut microbiota will produce beneficial compounds called short chain fatty acids (acetate, butyrate and propionate). These compounds have many fascinating roles in the body - one of which being to stimulate our immune system.

Eating fibre helps fuel our gut microbiota to work at its best; some of these fibres can be referred to as prebiotic. We can make the most of our fibre intake by including a range of different fruits, vegetables and whole grains (oats, nuts, seeds, brown rice, quinoa etc). Try switching some meat or animal-based protein with plant-based alternatives containing fibre - such as tofu, chickpeas, baked beans and other pulses/beans.

Whilst on the topic of bacteria, often fermented foods come into conversation. These are foods by which microbes (this includes bacteria, yeast etc) are added; for preservation or to alter flavour. Think bread, yoghurt, cheese, wine, sauerkraut, kimchi, kombucha or soy sauce. These foods have been all the rage in supermarkets for their supposed health benefits and microbial properties.

But not all fermented products are equal. For example, some microbes will not survive the fermenting processes, so we may not get their benefits. The foods that maintain live bacteria are referred to as probiotics. Probiotic foods include yoghurts (check the label as not all contain live bacteria), kefir, sauerkraut, miso and kimchi. Unfortunately there is a lack of strong evidence for the benefits of fermented foods on our immune health (in humans particularly). But fermented products have been around for many years, taste great (miso is life), often contain other nutrients and can be great to experiment with - so why not?

Vitamins and minerals

Yes, vitamin C does have a vital role in our immune function. However, so does vitamin A, vitamin D, vitamin E, some B vitamins and zinc. The deal is that we don't eat nutrients, we eat food. This means that when we eat food we eat a number of different nutrients. So, its almost impossible to miss out on these key nutrients if we‘re eating a varied and balanced diet.

Consuming more of a vitamin or mineral in a supplement will not supply our body with extra nutrients per se (unless we are deficient). Instead our body will excrete these, making for some pricey urine. Then in some cases, consuming more nutrients than we need can be toxic and harmful. For example: beta-carotene, vitamin B3, vitamin B6, selenium and even vitamin C. This is almost impossible to do through diet alone; toxicity occurs when these nutrients are supplemented in high doses.

Try and source nutrients from food first. Great sources of key nutrients for immune function include:

Vitamin A (includes beta-carotene): an anti-oxidant that is essential for production of antibodies (these are produced to fight a virus or bacteria). Found in carrots (cooked), butternut squash, sweet potatoes, leafy greens and eggs.

Vitamin C: an anti-oxidant that stimulates the action of protective white blood cells. Yes, there is some moderate evidence for vitamin C in reducing the length and severity of a cold - but a cold is not the same as COVID19. Found in most fruit and vegetables so it’s hard to miss, as long as we’re eating 5 portions a day. Good sources include kiwis, peppers, broccoli, lemons, oranges and brussel sprouts. Unlike vitamin A (betacarotene more specifically) often cooking these can reduce their nutritional benefits - so serve al dente.

Vitamin D: regulates antibacterial proteins. Found in oily fish, eggs, mushrooms and full fat dairy.

Vitamin E: an anti-oxidant that stimulates protective T-cells. Found in many nuts, corn and sunflower oil.

Selenium: an anti-oxidant, but beware as too much can have the opposite effect (pro inflammatory = bad). Found in brazil nuts, whole grains and fish.

Iron: supports protective T-cells and forms part of anti-oxidant enzymes. Found in red meat (haem iron which is more readily absorbed), soybeans, tofu, sesame seeds, tahini and pulses.

Zinc: modules immune effect. Found in sesame seeds, sunflower seeds, pulses, cheese and meat.

The only supplement that I recommend taking is vitamin D (primarily produced in skin by sun exposure), as have little sun here in England. In fact, everyone should be taking a vitamin D supplement, as recommended by Public Health England for bone and muscle health. Vitamin D has also been linked to lower rates of upper respiratory tract infections, and may increase the production of proteins that act similar to antibiotics. A supplement of 10 micrograms per day of vitamin D is recommended (from the age of 1 years old).


Adequate nutrition is key to support many bodily functions, and plays an important part in your immune function. Aim for a variety of foods, balanced meals and enough calories. Those who are at risk of deficiencies (elderly, coeliac disease, bariatric surgery patients, vegans etc) consider supplementation; particularly vitamin D if you are living in the UK. Chugging down orange juice and buying into the latest supplements may be doing little for our immune function, and may actually be doing more harm than good.

Please do remember that nutrition is just one element here. Other factors that have been linked to healthy immune function include regular exercise and stress management (consider meditation, yoga, mindfulness or other outlets).

Disclaimer: this blog article is written for educational and entertainment purposes, it is not written to provide bespoke advice. If you are requiring personalised advice or help, please get in contact with your GP or healthcare professional who can signpost you to registered dietitian or nutritionist.

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