A nutritionally balanced diet trumps supplements as whole foods are the most effective way for your body to use and absorb micronutrients. Having said that, current food supplies and patterns of eating make it challenging to obtain adequate amounts from diet alone and supplements can bridge this gap, with the caveat that you buy a quality product without unnecessary fillers and get the right dose, at the right time.
Let me explain: I was on a multivitamin for a while and it did not improve my health condition. Here’s the why: multivitamins are not individualised to you. The dose of supplements required depend on the health status of the person. Optimal nutritional support for the immune system can require intakes above the recommended daily, when infections and other stressors increase the demand for micronutrients and these stores need to be replenished accordingly. These may warrant higher doses of certain micronutrients under medical supervision.
So what do I mean by micronutrients?
A micronutrient is a vitamin, mineral or trace element that your body cannot make adequately and must be consumed from the diet. Nutrient deficiencies can increase the risk of infections and delay recovery. There is a complex interplay of micronutrients in the biological pathways where subsequent pathways are dependent on the availability other nutrients, so each part contributes to the whole. This could explain why various research papers found inconsistent results when only single micronutrients or select combination of micronutrients were studied.
A wealth of research show that micronutrients, including vitamins A, B6, B12, C, D, E, and folate; trace elements, including zinc, iron, selenium, magnesium, and copper; and the omega-3 fatty acids play important and complementary roles in supporting the immune system[i],[ii],[iii]
Let’s jump into it…..

Vitamin A
Vitamin A is important for eye health, proper cell development and maintaining heathy skin barrier and mucus that line the airways, digestive tract and urinary tract function; our first line of defence against infections. For an infection to develop, the invader must get close enough to interact with our cells. Physical barriers like our skin provide physical protection, while chemical barriers like mucus and enzymes, such as lysozyme in snot and tears and the acid in the stomach, also kill these invaders.
Not surprisingly, vitamin A deficiency is associated with immune deficiency[iv]. Dietary sources of vitamin A include liver, bright orange fruits and vegetables.
There have been concerns that too much vitamin A in supplement form can be toxic thus it is best to obtain vitamin A from dietary sources. The upper level intake of vitamin A supplementation is 3000 mcg or 10,000IU daily.
Aiming for the more conservative 10,000IU from safer diet-based source of Vitamin A from food: chicken liver 110g/week (5000 IU daily), 2-3 eggs daily and 4 cups of vegetables daily sounds like the right balance to me.
If you do not tolerate these foods, I would consider supplementing with cod liver oil.
Caution with doses higher than 5,000IU (supplements and diet-based) in pregnant women as it may cause fetal malformations.
Vitamin D
Vitamin D is an immune modulator. The form of vitamin D that is important to know is Vitamin D3 or also known as cholecalciferol and 25-hydroxyvitamin D (25OHD).
Vitamin D3 is made when the sun hits our skin or can obtained from diet or supplementation.
Vitamin D3 is then converted into 25OHD in the liver, an active form of vitamin D that circulates throughout the body. It is 25OHD that we measure in blood tests, with optimal serum levels above 50 nmol/L.
Dietary sources include fatty fish (salmon, herring, fish liver oils, eggs) although food are relatively minor sources of vitamin D. The upper level of dietary intake for adults is 80 mcg/day (3200IU cholecalciferol).[v] In severe deficiencies, higher doses may be required: it’s best to monitor serum 25OHD and adjust dose accordingly.
A study linked vitamin D-deficiency with poorer Covid-19 patient outcomes.[vi] Magnesium is essential to make vitamin D hence ensure adequate intake as well.[vii]
Vitamin E
Vitamin E is a key immunomodulator. It also acts as an antioxidant, clearing up free radicals built up from lipid peroxidation. Vitamin E works synergistically with vitamin C and glutathione to reduce further free radicals[viii]. The recommended daily dose of vitamin E is around 10mg in adult males and 7mg in adult females. Vitamin E cannot be made in the body so must be consumed through foods.
Vitamin K2
Vitamin K generally comes in 2 forms: K1 and K2. Research is catching up with Vitamin K2 in recent years; compared to vitamin K1, vitamin K2 has better absorption, lasts longer, and transports well around the body.[ix],[x]
There is a hypothesis that vitamin K deficiency is prevalent in patients with COVID-19 so make sure you get enough of this. Vitamin K1 is easily sourced from leafy green vegetables however K2 may not be commonly found in the Western diet hence Vitamin K2 supplementation may prove beneficial.
Best dietary source of K2: liver, aged cheese, natto
Micronutrient | Mechanism | Dietary Sources | Preferred Food/Supplement |
Vitamin A | eye health, proper cell development and maintaining heathy skin barrier and mucus | liver, bright orange fruits and vegetables | Aim for 10,000IU from safer diet-based source: chicken liver 110g/week (5000 IU daily), 2-3 eggs daily and 4 cups of vegetables daily. Max 5,000IU in pregnant women If you do not tolerate these foods, consider cod liver oil Rosita Real foods as its manufacturing process monitors for heavy metal contamination and maintains the integrity of the oil. |
Vitamin D | immune modulator | fatty fish (salmon, herring, fish liver oils, eggs) although food are relatively minor sources of vitamin | Increase sun exposure and supplement: Now Foods Vitamin D 5000IU dose-adjusted to target blood levels. Magnesium is essential to make vitamin D hence ensure adequate intake as well.[i] |
Vitamin E | antioxidant, clearing up free radicals built up from lipid peroxidation. Vitamin E works synergistically with vitamin C and glutathione to reduce further free radicals[ii]. | nuts, seeds and palm oil | Supplement Jarrow Formulas Toco-Sorb as it contains a good mix of different vitamin E precursors |
Vitamin K | Regulates blood coagulation | Vitamin K1 (green leafy vegetables) Vitamin K2 (liver, aged cheese, natto) | Supplement InnovixLabs Full Spectrum Vitamin K2 Caution if you’re on an anticoagulant as warfarin dose may needs to adjusted with addition of vitamin K2. |
Magnesium | convert food to energy (ATP) co-factor to make Vitamin D Rebalance immune cells | almonds, bananas, beans, broccoli, cashews, egg yolk, fish oil, flaxseed, green vegetables, mushrooms, other nuts, oatmeal, pumpkin seeds, sesame seeds, sunflower seeds | Now Magnesium Glycinate powder or Be Pure Magnesium Restore |
Zinc | immune-modulator, co-factor to enzyme pathways | Oysters, red meat, poultry | Jarrow Formulas Zinc Balance and Life Extension Enhanced Zinc lozenge (30 mins before exposure to public events etc) |
Vitamin C | antioxidant | fresh vegetables and fruits like acerola, berries, cauliflower, citrus fruits, and kiwifruit. | California Gold 500mg or Garden of Life Vitamin C 250mg |
B Vitamins | Necessary for a healthy immune system | 1 capsule daily | Orthoplex BioEnhanced Methyl-B (Practitioner Only) MTHFR Support Total Methyl B (Practitioner Only) Seeking Health B Complex Plus (You may need to top-up B12) |
Selenium & Iodine | To make thyroid hormones (regulates energy production and oxygen consumption) | selenium: Brazil nuts iodine: Seaweed | Now Potassium with Iodine |
Magnesium
Magnesium is an essential co-factor to make vitamin D so ensure adequate intake as well.[xi],[xii]
Magnesium rebalances immune cells and can tone down the cytokine storm, that causes hyperinflammation resulting in severe COVID-19. It is also an important player in activating vitamin D[xiii]
Zinc
Zinc is required for a robust immune system and provides structural, enzymatic and regulatory support to the body[xiv]. Oysters are considered the best source of zinc, followed by red meat and poultry.
- Zinc can reduce viral replication in the common cold. By the same token, case reports[xv] have shown that high dose zinc can reduce the symptoms of coronavirus disease 2019 (COVID-19) The upper level of dietary intake for adult men and women are 40 mg/day.
Zinc formulations with documented benefit include zinc acetate, citrate, glycine, gluconate and methionine. For doses above 40mg elemental Zinc/day, ensure adequate copper, with a 15:1 zinc: copper ratio to reduce the risk of copper deficiency.
To optimise zinc absorption, avoid taking zinc with whole grains, nuts, seeds, legumes or coffee.
Vitamin C
Vitamin C protects cell from the end-products of oxidative stress[xvi],[xvii]. Some studies suggest that the administration of vitamin C may increase the survival rate in COVID-19 patients, by reducing the cytokine storm however other studies produced conflicting results[xviii],[xix],[xx]
It is an essential micronutrient that the body cannot make and dose-adjusted to individual requirements, with the upper level intake at 1000-2000mg daily. Vitamin C is water-soluble and cleared by the kidneys. For those trying to clear an infection or under stress, higher doses may be beneficial in response to your body’s requirements. However, too much vitamin C may result in diarrhoea.
For prevention, supplement with 250mg mg three times daily and increase up to 500mg four times daily or dose to diarrhoea to prevent a colds or infection. Caution using high-dose vitamin C supplementation in those with a history of kidney stones, genetic disorders (e.g. hemochromatosis, glucose 6-phosphate dehydrogenase deficiency) or anticancer agents, speak to your trusted health professional first before supplementing.
B vitamins
The European Food Safety Authority (EFSA) determined that B-group vitamins (especially B6, Folate, and B12 as necessary for a healthy immune system. Toxicity is possible with B3, B5, B6 so dietary sources are safest.

Thyroid minerals: Selenium & Iodine
Our thyroid regulates energy production and oxygen consumption by setting the pace of our metabolism (breaking down food into energy), how fast your heart pumps and produces essential building blocks of the nervous and immune system. To make thyroid hormones, you need iodine and selenium. The immune system utilises iodine to fight against infection[xxi] and selenium to facilitate these enzyme pathways[xxii]. A great source of selenium is 2-3 brazil nuts a day. Other main dietary sources include seafood, poultry and eggs. The upper level of intake for adult males and females is 400mcg/day[xxiii].
As too much selenium can cause toxicity, aim to get most from diet
Ensure adequate selenium, vitamin C and magnesium intake as these work in collaboration. The upper level intake of iodine is 1100 mcg/day for adults[xxiv]. In general, thyroid dysfunction is prevalent in the community and before starting iodine supplementation, ensure that you do not have an autoimmune disorder. Check thyroid antibodies and other thyroid markers closely with your health care professional before starting iodine supplementation.
To refresh on the 10 steps to boost the immune system, click here
To read Step 1: Minimise toxins, click here
To read Step 2: eat a diverse diet, click here
References:
[i] Iddir M, Brito A, Dingeo G, Fernandez Del Campo SS, Samouda H, La Frano MR, Bohn T. Strengthening the Immune System and Reducing Inflammation and Oxidative Stress through Diet and Nutrition: Considerations during the COVID-19 Crisis. Nutrients. 2020; 12(6):1562. https://doi.org/10.3390/nu12061562
[ii] Gombart AF, Pierre A, Maggini S. A Review of Micronutrients and the Immune System–Working in Harmony to Reduce the Risk of Infection. Nutrients. 2020; https://doi.org/10.3390/nu12010236 , 12(1):236
[iii] Marcos A. Editorial: A Review of Micronutrients and the Immune System—Working in Harmony to Reduce the Risk of Infection. Nutrients 2021; https://doi.org/10.3390/nu13114180 , 13(11):4180.
[iv] Lewis P Rubin, A Catharine Ross, Charles B Stephensen, Torsten Bohn, Sherry A Tanumihardjo, Metabolic Effects of Inflammation on Vitamin A and Carotenoids in Humans and Animal Models, Advances in Nutrition, Volume 8, Issue 2, March 2017, Pages 197–212,
[v] NHMRC, NZ MOH. Nutrient Reference Values.2006 https://www.nrv.gov.au/nutrients (accessed 13/1/22)
[vi] Munshi, R, Hussein, MH, Toraih, EA, et al. Vitamin D insufficiency as a potential culprit in critical COVID-19 patients. J Med Virol. 2021; 93: 733- 740. https://doi.org/10.1002/jmv.26360 (accessed 13/1/22)
[vii] Deng X, Song Y, Manson JE, et al. Magnesium, vitamin D status and mortality: results from US National Health and Nutrition Examination Survey (NHANES) 2001 to 2006 and NHANES III. BMC Med. 2013;11:187. Published 2013 Aug 27. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3765911/
[viii] Lee GY, Han SN. The Role of Vitamin E in Immunity. Nutrients. 2018; https://doi.org/10.3390/nu10111614 , 10(11):1614.
[ix] Kozioł-Kozakowska A, Maresz K. The Impact of Vitamin K2 (Menaquionones) in Children’s Health and Diseases: A Review of the Literature. Children. 2022; 9(1):78. https://doi.org/10.3390/children9010078
[x] Přemysl Mladěnka, Kateřina Macáková, Lenka Kujovská Krčmová, Lenka Javorská, Kristýna Mrštná, Alejandro Carazo, Michele Protti, Fernando Remião, Lucie Nováková, on behalf of the OEMONOM researchers and collaborators, Vitamin K – sources, physiological role, kinetics, deficiency, detection, therapeutic use, and toxicity, Nutrition Reviews, 2021;, nuab061, https://doi.org/10.1093/nutrit/nuab061
[xi] Dai Q, Zhu X, Manson JE, et al. Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial. Am J Clin Nutr. 2018;108(6):1249-1258. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6693398/ (accessed 13/1/22)
[xii] Uwitonze, Anne Marie and Razzaque, Mohammed S.. “Role of Magnesium in Vitamin D Activation and Function” Journal of Osteopathic Medicine, vol. 118, no. 3, 2018, pp. 181-189. https://doi.org/10.7556/jaoa.2018.037
[xiii] Uwitonze, Anne Marie and Razzaque, Mohammed S.. “Role of Magnesium in Vitamin D Activation and Function” Journal of Osteopathic Medicine, vol. 118, no. 3, 2018, pp. 181-189. https://doi.org/10.7556/jaoa.2018.037
[xiv] Roohani N, Hurrell R, Kelishadi R, Schulin R. Zinc and its importance for human health: An integrative review. J Res Med Sci. 2013; 20/9/21), 18(2):144-157. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3724376/ (accessed 27/1/22)
[xv] 2020, Finzi E. Treatment of SARS-CoV-2 with high dose oral zinc salts: A report on four patients. Int J Infect Dis.; doi:10.1016/j.ijid.2020.06.006, 99:307-309
[xvi] Ahmed, M.H., Hassan, A. & Molnár, J. The Role of Micronutrients to Support Immunity for COVID-19 Prevention. Rev. Bras. Farmacogn. 31, 361–374 (2021). https://doi.org/10.1007/s43450-021-00179-w (accessed 13/1/22)
[xvii] Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017; 9(11):1211. https://doi.org/10.3390/nu9111211 (accessed 13/1/22)
[xviii] Bae, M.; Kim, H. The Role of Vitamin C, Vitamin D, and Selenium in Immune System against COVID-19. Molecules 2020, 25, 5346. https://doi.org/10.3390/molecules25225346 (accessed 13/1/22)
[xix] Cámara M, Sánchez-Mata MC, Fernández-Ruiz V, Cámara RM, Cebadera E, Domínguez L. A Review of the Role of Micronutrients and Bioactive Compounds on Immune System Supporting to Fight against the COVID-19 Disease. Foods. 2021; 10(5):1088 https://doi.org/10.3390/foods10051088 (accessed 13/1/22)
[xx] Milani GP, Macchi M, Guz-Mark A. Vitamin C in the Treatment of COVID-19. Nutrients. 2021;, 13(4):1172 https://doi.org/10.3390/nu13041172 (accessed 13/1/22)
[xxi] Bilal MY, Dambaeva S, Kwak-Kim J, Gilman-Sachs A, Beaman KD. A Role for Iodide and Thyroglobulin in Modulating the Function of Human Immune Cells. Front Immunol. 2017;8:1573. Published 2017 Nov 15. doi:10.3389/fimmu.2017.01573
[xxii] Avery JC, Hoffmann PR. Selenium, Selenoproteins, and Immunity. Nutrients. 2018; https://doi.org/10.3390/nu10091203 , 10(9):1203.
[xxiii] Australian National Health and Medical Research Council (NHMRC), Australian Government Department of Health and Ageing and the New Zealand Ministry of Health (NZ MoH). Nutrient Reference Values. 2017 https://www.nrv.gov.au/nutrients
[xxiv] Australian National Health and Medical Research Council (NHMRC), Australian Government Department of Health and Ageing and the New Zealand Ministry of Health (NZ MoH). Nutrient Reference Values. 2017 https://www.nrv.gov.au/nutrients
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