Immunonutrition 101: boosting the immune system

In the past few months there has been a lot of attention on supplements that can improve your ability to fight colds.

Supplements can help strengthen your immune system and many of them are taken to improve thyroid function.

Recent research has shown that vitamin D and zinc are two major supplements that aid in fighting the severe effects of many acute illnesses that affect the respiratory system (1, 2).

Both vitamin D and zinc are highly beneficial for thyroid function and reducing Hashimoto’s flare-ups.

Vitamin D and your immune system

Vitamin D plays a critical role in helping your immune system function optimally by (3):

  • Blocking molecules that promote inflammation
  • Reducing lung damage
  • Strengthening your immune system

Adults who are at risk of vitamin D deficiency include (4):

  • People with celiac disease, inflammatory bowel disease, and cystic fibrosis
  • The elderly
  • People who have low sun exposure (less than 20 minutes daily of exposing ½ of your skin)
  • People with liver cirrhosis
  • People who take medications such as phenobarbital, carbamazepine, dexamethasone, nifedipine, spironolactone, clotrimazole, and rifampin

Symptoms of vitamin D deficiency include (4):

  • Bone pain
  • Joint pain
  • Fatigue
  • Muscle pain, twitching, and weakness

Low vitamin D levels are defined as (5, 6):

  • Deficiency: less than 20 ng/ml
  • Insufficiency: between 21 and 29 ng/ml

If you have low levels, you can supplement with vitamin D2 or vitamin D3. It might take about eight weeks of treatment to reach the recommended blood levels (6).

How much vitamin D do you need?

Adults require a 600–800 IU (15–20 µg) daily dietary intake of vitamin D (5, 6).

The recommended dietary allowances for vitamin D are (5,6):

  • 0–12 months old → 400 IU (10 mcg)
  • 1–70 years old → 600 IU (15 mcg)
  • >70 years old → 800 IU (20 mcg)

Zinc and your immune system

Zinc is known to prevent acute respiratory infections in young children and adults.

It may potentially lower the risk of contracting respiratory infection, and shorten the length or severity of the disease (2). Daily recommended intake (RDI) of zinc is 2mg for children under 13 years, 8mg for females older than 13 years, and 11mg for males older than 13 years (7).

High doses of zinc or prolonged intake can cause anosmia — a loss of smell (8). Zinc is an essential part of the enzyme deiodinase, which converts T4 into functional T3. If zinc levels are low, T3 can’t be made (9).

Zinc has an important role in helping your immune system by (2):

  • Helping to build up immune cells that fight viruses and bacteria
  • Regulating how your body initially responds to viruses and bacteria
  • Enhancing molecules that fight infection

Adults at risk of zinc deficiency include people who (10–19):

  • Consume a predominantly plant-based diet
  • Consume high levels of cereals, potatoes, and legumes
  • Have chronic diseases (including IBS, anemia, and lung diseases)
  • Have a high alcohol intake

Symptoms of zinc deficiency include (20):

  • Slow wound repair
  • Recurrent infections
  • Headaches
  • Brain fog
  • Rough skin and thinning hair

Zinc supplements should be taken at least four hours apart from your thyroid medication, as they might prevent the uptake of thyroid medication in your gut.

How we write: our information is based on the results of peer reviewed studies using the National Library of Medicine platform. It is written by scientists and reviewed by external experts. If you believe we might have overseen crucial scientific information, please contact us at

Disclaimer: This information is not intended to mitigate, prevent, treat, cure or diagnose any disease or condition. If you want to change your treatment, lifestyle, your diet, include supplements in your diet or have concerns about your health, please consult your doctor before trying new approaches.


  1. Alexander J, et al. Early Nutritional Interventions with Zinc, Selenium and Vitamin D for Raising Anti-Viral Resistance Against Progressive COVID-19, 2019
  2. Arentz S, et al. Zinc for the prevention and treatment of SARS-CoV-2 and other acute viral respiratory infections: a rapid review, 2020
  3. Mora JR, et al. Vitamin effects on the immune system: vitamins A and D take centre stage, 2008
  4. Sizar O, et al. Vitamin D Deficiency, 2020
  5. Muscogiuri G, et al. Vitamin D and thyroid disease: to D or not to D, 2015
  6. Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline, 2011
  7. Institute of Medicine Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc , 2011
  8. Eby GA, et al. Ineffectiveness of zinc gluconate nasal spray and zinc orotate lozenges in common-cold treatment: a double-blind, placebo-controlled clinical trial, 2006
  9. Baltaci AK, et al. Opposite effects of zinc and melatonin on thyroid hormones in rats, 2004
  10. Allen LH. The nutrition CRSP: what is marginal malnutrition, and does it affect human function, 1993
  11. Ruel MT, et al. Plant breeding: a long-term strategy for the control of zinc deficiency in vulnerable populations, 1998
  12. Ferguson EL, et al. Dietary calcium, phytate, and zinc intakes and the calcium, phytate, and zinc molar ratios of the diets of a selected group of East African children, 1989
  13. Foster M, et al. Effect of vegetarian diets on zinc status: a systematic review and meta‐analysis of studies in humans, 2013
  14. Shah D, et al. Effect of gestational zinc deficiency on pregnancy outcomes: summary of observation studies and zinc supplementation trials, 2001
  15. Hess S, et al. Effects of maternal zinc supplementation on pregnancy and lactation outcomes, 2009
  16. Karimi A, et al. Zinc deficiency in pregnancy and fetal-neonatal outcomes and impact of the supplements on pregnancy outcomes, 2012
  17. Fraker PJ, et al. The dynamic link between the integrity of the immune system and zinc status, 2000
  18. Tudor R, et al. Zinc in health and chronic disease, 2005
  19. Mehta AJ, et al. Alcoholism causes alveolar macrophage zinc deficiency and immune dysfunction, 2013
  20. Prasad AS. Molecular, Genetic, and Nutritional Aspects of Major and Trace Minerals. Discovery of zinc for human health and biomarkers of zinc deficiency, 2017

Photo: Unsplash; Design: VLM Health

Originally published at on November 6, 2020.



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