Coping with IBS during COVID-19 #3: Optimising nutrition for the immune system

Nutrition and the immune system

Dakota Rhys-Jones - Research Dietitian, 08 April 2020

The immune system and nutrition:

All systems of the body, including the immune system, rely on adequate nutrition for their optimal function. We know that there are certain subgroups of the community who are at increased risk of infection due to a decreased immune response, including the elderly, who are also more likely to be at risk of malnutrition (1). Importantly, adequate nutrition is not going to ‘boost’ your immunity, instead, it will ensure your body is working optimally to fight off disease causing viruses or bacteria. 

So, what exactly is the immune system?

The immune system is a very complex collection of cells, tissues and molecules that act as our bodies defence against foreign material (2). Kind of like the army, or military, protecting the country from invasion. The coronavirus is a ‘foreign material,’ so essentially, adequate nutrition will help to support our immune system in fighting off the virus.

Outlined below are particular nutrients of importance to maintain the health of the immune system, as well as rich food sources to find them. At the moment we are seeing globally lots of panic buying, including nutritional supplements, which is not necessary, unless prescribed by a health professional. Eating whole foods is more important than singling out nutrients, and are also more enjoyable, as healthy, nutritious meals can be shared with friends or family, if you are lucky enough to live in a home with them. 

Micronutrient Food sources (check the app for low FODMAP portion sizes)
Vitamin C Strawberries, citrus fruit, capsicum, kiwi fruit
Zinc* Meat, fish, poultry, shellfish, legumes, seeds
Selenium* Poultry, eggs, brazil nuts, salmon
Vitamin D Fatty fish, egg yolk, fortified margarines + dairy products.
Note: very few foods contain significant amounts of Vitamin D – sunlight is the better source.
*Meat/poultry sources are in the raw form – look out for marinades or crumbs that contain high FODMAP sources.

Vitamin C

Vitamin C is essential, meaning the body cannot make it itself and it needs to be acquired through the diet (3). Its antioxidant properties protect immune cells from damage, where it can help to fight off free radicals (4). Free radicals cause damage and stress to cells, so it is important they are cleaned up by antioxidants. Vitamin C helps to increase production of certain subsets of immune cells, and is critical for collagen synthesis (4). Collagen increases the integrity of the skin and supports wound healing, another critical response in avoiding infection (4).

Vitamin D

Vitamin D is a fat-soluble vitamin that is most commonly known for playing an essential role in bone health (3). However, receptors for vitamin D have also been found in the heart, kidney, gut, as well as immune cells (5). The active form of Vitamin D can increase production of certain immune cells, and a deficiency is associated with some autoimmune conditions (i.e. Type 1 Diabetes + inflammatory bowel disease), as well as susceptibility to infections (5). Vitamin D comes from two sources: the sun and foods (see table above). It might be harder for some to get outside than others due to varying degrees of isolation globally. If you can, even for 5 minutes, expose your skin to the sun every day to stimulate vitamin D production and breathe in some fresh air. For those who may be worried about lack of sun exposure, vitamin D gets stored in the body, so that during winter months, our body can use the saved up stores from summer (3). 

Zinc + Selenium

Zinc and selenium are both trace elements, that are components of many enzymes in the body. They can both help to protect cells from oxidative damage through detoxifying free radicals and increase the growth of immune cells (3). A deficiency of both results in a decreased immune response. Zinc is also important for DNA synthesis, the maintenance of cell membranes, and helps to regulate wound healing (3).

If you are following a vegetarian or vegan diet, your zinc requirements may be up to 50% higher due to decreased absorption of zinc from plant-based sources (3). This is due to the phytates that are found in vegetarian sources of zinc, that inhibit zinc absorption (6). Some ways to boost zinc absorption include techniques such as soaking, sprouting and fermentation of legumes, grains and nuts (6). These methods can also help to reduce the FODMAP content e.g. activated cashews, which have undergone a soaking then drying process, have a green serve in the app. Yeast fermentation of wheat to make sourdough breads also helps to destroy the phytate, which reduces that inhibitory effect and improves zinc absorption (6).

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1.            Marcos A, Nova E, Montero A. Changes in the immune system are conditioned by nutrition. European Journal of Clinical Nutrition. 2003;57(S1):S66.

2.            Maggini S, Pierre A, Calder PC. Immune Function and Micronutrient Requirements Change over the Life Course. Nutrients. 2018;10(10):1531.

3.            NHMRC. Nutrient Reference Values Canberra: NHMRC; 2020 [Available from:

4.            Carr A, Maggini S. Vitamin C and Immune Function. Nutrients. 2017;9(11):1211.

5.            Bikle D. Nonclassic actions of vitamin D. J Clin Endocrinol Metab. 2009;94(1):26-34.

6.            Saunders AV, Craig WJ, Baines SK. Zinc and vegetarian diets. Medical Journal of Australia. 2013;199(S4):S17-S21.

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