Strengthening your immune system

The best way to fend off viruses and infections is to strengthen your immune system. There are many nutrients which help to build up your first line of defence and help avoid colds and flus.

Below are some tips and strategies to strengthen your own defences and decrease your susceptibility to infection.

Immune boosting nutrients:

Vitamin C is a potent antioxidant and one of the most important nutrients for the immune system.

It serves many different functions, including supporting the production of antibodies and a protein called interferon which is able to stop the proliferation of viruses by destroying the infected cell, as well as inhibiting the production of an enzyme which bacteria and viruses use to protect themselves against our defences.

Some of the best sources of vitamin C are:

  • papaya
  • bell peppers
  • broccoli
  • brussels sprouts
  • strawberries
  • pineapple
  • oranges
  • kiwifruit
  • cantaloupe
  • cauliflower
  • kale
  • cabbage
  • bok choy
  • grapefruit
  • parsley
  • swiss chard
  • tomatoes
  • lemons and limes
  • spinach
  • asparagus
  • thyme

Vitamin A is best known for its role in promoting good eyesight, but it also works as an anti-oxidant and plays a critical role in enhancing immune function such as maintaining the integrity of the mucosal barriers of our eyes, lungs and guts which help to trap bacteria and virus particles.

Vitamin A in the form of beta-carotene has an orange hue which is present in food. Therefore, as a rule of thumb if a food is orange it will be a good source of vitamin A.

Some of the best sources of vitamin A are:

  • liver
  • sweet potato
  • carrots
  • prawns
  • spinach
  • eggs
  • kale
  • cow’s milk
  • swiss chard
  • cheese
  • bok choy
  • yogurt
  • cantaloupe
  • salmon
  • bell peppers
  • sardines
  • parsley
  • chicken
  • asparagus
  • cod liver oil
  • tomatoes
  • papaya
  • brussel sprouts
  • basil 


Vitamin D 
acts as a hormone in the body and helps to regulate the immune response.

It also appears capable of inhibiting pulmonary inflammatory responses while enhancing innate defence mechanisms against respiratory pathogens.
Unfortunately, the list of vitamin D-rich foods is quite short and even one of the best dietary sources (milk) is only rich in vitamin D because it has been fortified with it.

The best source of vitamin D is therefore sun exposure, but during these times when we are unable to rely so readily on it, the easiest way to increase vitamin D is salmon which contains more than the daily requirement in a single serving. Sardines contain over 40% of the daily requirement and tuna just under 25%.

Eggs contain around 10% of the RDA (recommended daily allowance) per egg, concentrated in the yolk. Some mushrooms such as shiitakes contain around 5% per 100g.

Also, cod liver oil contains both vitamin A and vitamin D in high concentrations, making it an excellent choice.

Zinc is the most important trace mineral for the immune system.
It is crucial for the normal development and function of immune cells and is a potent anti-inflammatory.

Some of the best sources of zinc are:

  • beef
  • spinach
  • asparagus
  • mushrooms, shiitake
  • lamb
  • sesame seeds
  • pumpkin seeds
  • chickpeas
  • lentils
  • prawns
  • broccoli
  • green peas
  • swiss chard
  • yogurt
  • brussels sprouts
  • miso
  • parsley
  • tomatoes
  • oats
  • bok choy

Probiotics: Around 70% of our entire immune system calls our gut its home.
Therefore, for a healthy immune system we need to look after our gut flora and ensure that our microbial residents have a good variety of different other bacterial housemates in there with them.

A great source of probiotic foods includes fermented foods such as:

  • kefir
  • sauerkraut
  • kimchi
  • kombucha
  • natural yogurt
  • tempeh (fermented soybeans)
  • miso

Just as heat kills bad bacteria in foods during cooking, it will also kill any good bacteria that would have been present in the food. Many store-bought fermented foods such as sauerkraut will have been heat-treated and will have therefore lost any probiotic benefit. It is also very easy to make at home.

man and fermented food

Hints and tips:

Try to pair these foods at meals so that you are getting the benefits of all the immune-boosting vitamins, such as:

  • Salmon, asparagus, broccoli and sauerkraut.
  • Eggs (omelette), spinach, mushrooms, tomatoes.
  • Thai-style soup with miso, ginger, garlic, mushrooms, bok choy, red bell peppers, lime and prawns will contain all the above vitamins plus some added immune-boosting ginger and garlic. Adding hot chilli peppers will also increase the vitamin A and C content, whilst the capsaicin (what makes chilli peppers spicy) will help to clear congestion and phlegm.

Because many vitamins such as vitamin A and vitamin C are heat-sensitive, try not to overcook your vegetables.

Ginger and garlic have powerful antimicrobial, antiviral and immune-boosting properties.

The main active chemical in garlic is called allicin and it is activated when the garlic is sliced or crushed. Therefore, before cooking with garlic, chop/crush and let it sit for 5-10 minutes before exposing it to heat to maximise the amounts of allicin present in your garlic bread.

Honey is a fascinating ancient food with antimicrobial, antiviral, anti-inflammatory and anti-oxidant properties. Honey is also a humectant (draws in and holds on to water) and works as an antibacterial by soaking up all the fluid out of the bacteria like a dry sponge, in effect killing it. This, paired with its acidity, is the reason why honey never, ever spoils.

Unfortunately, many of the commercial “honey” sold in common supermarkets are not actually honey but honey syrup. In order to test if your honey is the real thing, swirl it around in water. Honey will not dissolve in cold liquid so if you are left with a blob of sticky mess at the bottom of your glass, you have the real thing. Heating also reduces the quality and kills many of its enzymes, so never add to boiling hot water.
Mushrooms are powerhouses for the immune system, containing powerful antibacterial, antifungal, antiviral, antioxidant and anti-inflammatory compounds.

One of the most potent mushrooms for the immune system is the shiitake mushroom, which has been shown to have anti-viral activities against many viruses.

Shiitake mushrooms inhibit the growth and proliferation of viruses by preventing an important process that the virus must go through in order to propagate.

Even the humble button mushroom boosts immune function by increasing the production of anti-viral proteins released by cells looking to protect and repair tissue. These fungal friends are also one of the few non-animal sources of vitamin D.

You must cook your mushrooms and never eat them raw. Mushrooms have a very tough cell wall which is indigestible in the raw form and cooking them will release their nutrients and make them available.

Other important things:

Sleep is important for immune function. During sleep, our immune system releases proteins called cytokines and these need to be increased when we are exposed to an infection. Sleep deprivation may decrease production of these protective proteins. Infection-fighting antibodies are also reduced.
Recent studies show that an average of 7 hrs minimum per night is required for optimal function and 9 hrs for those recovering from sleep debt or during illness.

Stress management is also important for maintaining a healthy and strong immune system. Our stress hormone is called cortisol and in short bursts it is beneficial to us and protects our immune system. This is why short-term stress such as exercise is so good for us. However, long-term sustained, high levels of cortisol will tire out the immune system and leave you more susceptible to illness and infection.

Nutritionist Resource is not responsible for the articles published by members. The views expressed are those of the member who wrote the article.

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