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Can we “boost” our immune response through the diet?

Perhaps an important question given the current circumstances. In short, no. The immune system is a very complex topic, with many different defence mechanisms. In order to support a normal functioning immune system, we should already be having a healthy and varied diet encompassing a wide variety of foods. We should be including fruits, vegetables, wholegrains, healthy fats and lean sources of protein. Aim for 30 different plant-based food sources a week (think fruits, vegetables, beans and pulses, wholegrains, nuts and seeds) and 30g of fibre a day wherever possible. For those who have restricted intakes, speak to your doctor or dietitian before taking supplementation. Special interest in particular nutrients which have a role in immunity may be beneficial if you are lacking them in your diet. However, the most important factor is to eat a healthy and varied diet and not to fixate on a single nutrient or a wonder pill.

Here are a few nutrients with specific roles in the immune system.

Vitamin A

Vitamin A is able to help strengthen our immune barrier by promoting mucus secretion and epithelium formation. In addition, vitamin A is needed for macrophage development, a type of protective white blood cell. Deficiencies of vitamin A can lead to a weakened immune system. Additionally, animal data has shown the vitamin A deficiency can impair T cell and antibody function.

Source of vitamin A include:

  • Liver
  • Dairy products
  • Yellow/orange/red fruits and vegetables such as peppers, sweet potato, carrots, papaya, mango
  • Dark green vegetables such as kale and spinach

Over consumption of vitamin A by supplementation can lead to vitamin A toxicity, so consult your doctor or dietitian before starting vitamin A supplementation. Special caution applies to pregnant women who are advised to avoid vitamin A supplements, liver and liver products due to the risk of birth defects.

A delicious roasted squash, lentil and kale salad, packed full of nutrients from A – Zinc.

Vitamin C

Vitamin C is involved in proliferation, function, and movement of neutrophils, monocytes, phagocytes, and is often the first nutritional supplementation turned to when a cold or flu strikes. Previous high-quality work has shown that high intakes of vitamin C are not associated with reducing the risk of contracting a cold in the ordinary population. However, consumption of a high dose (1000-2000mcg/d) was found to reduce the length and severity of a cold. The caveat of this was that this was only effective in those people who were already regularly taking these high doses.

Sources of vitamin C include:

  • Citrus fruits
  • Berries
  • Kiwis
  • Bell peppers and chilli
  • Kale
  • Potatoes

Over supplementation of vitamin C can lead to diarrhoea, nausea, kidney stones and expensive urine. The UK reference nutrient intake for most adults is 40mcg/day. Anything above this will be excreted.

Roasted red pepper and goats cheese salad which packs in a whopping 14.5g fibre per serving – recipe coming soon!

Vitamin D

Vitamin D is thought to be able to modulate the immune response and has been linked to inflammation and the immune system, which could be due to its role in the formation of T cells. Vitamin D has also been shown to protect the lungs against infection.

Most of our vitamin D will come from supplementation. The Scientific Advisory Committee for Nutrition (SACN) recommend supplementation of 10mcg[400IU]/d for most of the population, as dietary sources are rarely adequate on their own. This is of particular importance for those living in the UK and Ireland where skin exposure to sunlight will not produce any vitamin D between October and March.

Dietary sources of vitamin D include:

  • Fortified foods such as milk alternatives and cereals
  • Egg yolks
  • Oily fish
  • Liver, including cod liver oil*
  • UVB exposed mushrooms

High doses of vitamin D (above 25mcg[1000IU]/d) can lead to nausea, vomiting, kidney stones, irregular heartbeats and stiffening of the arteries.

My smoked mackerel pâté recipe additionally provides you with some omega 3 fatty acids.

*not suitable during pregnancy due to a high level of vitamin A

Vitamin E

Dietary interventions looking at vitamin E supplementation have been shown to enhance cell-mediated and humoral immune responses in animals. Vitamin E supplementation has also shown increased lymphocyte proliferation, immunoglobulin levels, antibody responses, natural killer cell activity, and interleukin-2 production. In addition, vitamin E’s antioxidant effects are thought to play a role in protecting the PUFA membrane from oxidation.

Sources of vitamin E include:

  • Most nuts (e.g. almonds, peanuts, hazelnuts) and seeds (e.g. sunflower, pumpkin)
  • Vegetable oils (e.g. sunflower, soybean, rice bran)
  • Wheatgerm (found in cereals)

There isn’t enough evidence to know what the effects might be of taking high doses of vitamin E supplements each day. In the UK, the safe intake is set at 4mg for men and 3mg for women per day. Any vitamin E not utilised immediately is stored, so you don’t need to have it in your diet every day.

Try making my cherry, chocolate and coconut granola and mix in different nuts if you can to maximise diversity.


Zinc deficiency has been found to negatively impact many cells related to the immune system, such as: neutrophils, natural killer cells, macrophages, B cells and T cells, and has a central role in cellular growth and differentiation of immune cells that have a rapid differentiation and turnover. Use of zinc acetate lozenges daily for up to one week was associated with reduced severity and duration of a cold, but only when taken within 24 hours of the first symptoms presenting. In a separate study, zinc gluconate lozenges significantly reduced the duration of illness in comparison with placebo but had no effect on symptom severity.

Dietary sources of zinc include:

  • Shellfish
  • Red meat and poultry
  • Eggs
  • Dairy products
  • Nuts and seeds
  • Chickpeas
  • Lentils
  • Wholegrains

Too much zinc in the diet can cause a reduced uptake of copper, leading to anaemia and weak bones.

An easy way to include zinc in the diet would be to add some shellfish, such as clams, to a pasta dish.


Probiotics can be important for helping boost the good bacteria in your gut. You gut is responsible for around 70% of your immune system and can impact on the production of white blood cells. Recent studies have shown a link between specific strains of lactobacillus, which may reduce the risk of viral infections. However, more research into this area is needed.

Probiotic sources include:

  • Kefir
  • Live yoghurts
  • Live kombucha
  • Unpasteurised fermented foods such as kimchi or sauerkraut

Alternative ways to help boost your gut bacteria could be the use of prebiotics. Prebiotics are types of carbohydrates which feed your gut bacteria. Prebiotic foods include:

  • Garlic, onion and leeks
  • Jerusalem artichokes
  • Asparagus
  • Oats
  • Banana
  • Flaxseeds

Watch out as not all fermented foods are equal. Additionally, some fermented foods may trigger those who suffer from IBS, so follow the guidance of your dietitian if you suffer from this. Additionally, use of probiotics in health living people may not be so beneficial, but that is because your gut bacteria are already doing well on their own. Keep them happy with plenty of diverse plant food sources and fibre.

Overnight oats are a simple way of including both pre- and probiotics


Garlic appears to  enhance the functioning of the immune system by stimulating certain cell types, such as macrophages, lymphocytes and natural killer cells. Previously, studies have found that an equivalent dose of 3-6 cloves of garlic as aged garlic extract may help to reduce the severity of colds and flus. However, aged garlic contains a compound called S-allyl cysteine not found in fresh garlic.

Garlic supplementation may cause interactions with medications such as blood thinners, anticoagulants, certain oral contraceptive pills and certain HIV medication. Consult your doctor before taking garlic supplements if you are on medication. Very high doses of garlic can also be toxic… or cause social isolation….

While I use garlic throughout my dishes, I simply love pesto. So versatile, you can use whatever you have to hand be it left over herbs, frozen peas or even vegetable tops such as carrots. Why not give my kale pesto a go – additionally a great source of vitamins ACE!


Capsaicin, the chilli pepper component that produces a burning sensation, can be effective against nasal congestion and lowering inflammation, thereby reducing symptoms of colds and flus. In addition, the pain from eating chillis can lead to the release of endorphines, the body’s natural pain killer, giving a feeling of happiness and wellbeing.

Overdoing chilli can lead to diarrhoea due to irritation of the stomach or intestinal lining; or irritate those with IBS.

For those who can, turn up the heat with an extra chilli or two in my vegan chickpea curry.

So what is the true answer? Eat (plenty of variety), drink (preferably not alcohol), sleep (7-9 hours a day) and repeat (washing your hands with soap).

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