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  • Writer's pictureJoshua Kleinstreuer

Vitamin D Supplements and COVID-19 Infections: What the Research Says

As the United States and the World continues to suffer from COVID-19 infections with no vaccine readily available, researchers are exploring all avenues possible to mitigate the effect of the pandemic. While mask-wearing and quarantines have helped to slow the spread, additional public health measures that can reduce the risk of infection and death are sorely needed. Some researchers are focusing on Vitamin D supplements based off of its success with similar symptoms from other infections.

The jury is still out on the true effectiveness of Vitamin D. There have been several clinical trials that reported that extra intake of vitamin D supplementation reduced the risk of influenza. However there also have been studies which found no effectiveness.

Calcifediol is a pre-hormone that is produced in the liver by hydroxylation of vitamin D₃. Physicians often measure this metabolite to determine a patient's vitamin D status.

Research supporting the role of vitamin D in reducing risk of COVID-19 include:

· Outbreak occurred in winter, a time when concentrations of Calcifediol are lowest

· Number of COVID-19 cases in SouthernHemisphere near the end of summer are low

· Vitamin D deficiency has been found to contribute to acute respiratory distress syndrome

· Case-fatality rates increase with factors associated with lower Calcifediol concentrations—such as old age and chronic disease comorbidity

These factors are leading some in the medical community to encourage anyone who is at risk of complications from influenza and/or COVID-19 to consider taking increased doses of Vitamin D3 supplements for a few weeks to rapidly raise Calcifediol concentrations in their body (Grant et al.).

In addition to reducing infections and spread in the community, research suggests that Vitamin D supplementation to increase Calcifediol blood level concentrations can help reduce hospital-associated infections (Youssef et al.). Study findings indicate that all health care providers as well as patients and staff, should consider taking vitamin D supplements to raise Calcifediol blood levels as an important step in preventing Healthcare Associated Infections (HAI).

Considerations for High-Doses of Vitamin D

It is important to note that, like with almost anything in life, there can be too much of a good thing.

Since Vitamin D aids with calcium absorption, too much of it will also lead to abnormally high calcium levels in your blood. High calcium levels, also known as hypercalcemia, can cause:

· digestive distress, such as vomiting, nausea, and stomach pain

· fatigue, dizziness, and confusion

· excessive thirst

· frequent urination

It is hard to set a universal standard concerning Vitamin D intake, as everyone’s body absorbs and processes vitamins and supplements differently. While the FDA has set a recommended daily intake for Vitamin D, anyone considering taking more should simply speak with their doctor first. There have been studies where people took excessive amounts of Vitamin D3 and it did not affect the incidence rate of kidney stone events or hypercalcemia (Malihi et al.).

Various federal agencies in the United States, including the FDA, U.S. Institute of Medicine, and others each have their own baseline for how much Vitamin D a person should consume on a daily basis which varies based on a person’s age, gender, and health status.

Natural Sources of Vitamin D

While supplements to boost your Vitamin D levels above the recommended daily intake are necessary to achieve the health benefits that could reduce the risk of infections or severity of symptoms, you may also obtain Vitamin D through your diet. Foods high in Vitamin D include:

· Cod liver oil

· Trout

· Salmon

· Mushrooms

· Milk

· Sardines

· Egg

· Liver

· Beef

· Tuna fish canned

If you are vegetarian or don’t like fish, it may be hard to find a natural source of Vitamin D. Fortunately, some food products that don’t naturally contain Vitamin D are fortified with it:

· Cow’s milk

· Soy milk

· Orange juice

· Cereal and oatmeal

In addition to Vitamin D supplements, health experts recommend taking Magnesium supplements, as research has shown all of the enzymes that metabolize vitamin D in the bloodstream require magnesium (Uwitonze & Razzaque).


The hypothesis that vitamin D supplementation can reduce the risk of the flu, COVID-19 infections, and the severity of COVID-19 symptoms which could potentially be fatal still needs further investigation. At this point in time, researchers have not established guidelines on concentration and dosage levels along with safety concerns (Han et al.).

Gombart and colleagues wrote in their article published in the journal Nutrients in January of 2020: “Although contradictory data exist, available evidence indicates that supplementation with multiple micronutrients with immune-supporting roles may modulate immune function and reduce the risk of infection. Micronutrients with the strongest evidence for immune support are vitamins C and D and zinc. Better design of human clinical studies addressing dosage and combinations of micronutrients in different populations are required to substantiate the benefits of micronutrient supplementation against infection.”.


Gombart A.F., Pierre A., Maggini S. A Review of Micronutrients and the Immune System-Working in Harmony to Reduce the Risk of Infection. Nutrients. 2020;12:236. doi: 10.3390/nu12010236.

Grant, W. B., Lahore, H., McDonnell, S. L., Baggerly, C. A., French, C. B., Aliano, J. L., & Bhattoa, H. P. (2020). Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients, 12(4), 988.

Han J.E., Jones J.L., Tangpricha V., Brown M.A., Brown L.A.S., Hao L., Hebbar G., Lee M.J., Liu S., Ziegler T.R., et al. High Dose Vitamin D Administration in Ventilated Intensive Care Unit Patients: A Pilot Double Blind Randomized Controlled Trial. J. Clin. Transl. Endocrinol. 2016;4:59–65. doi: 10.1016/j.jcte.2016.04.004.

Kaufman HW, Niles JK, Kroll MH, Bi C, Holick MF (2020) SARS-CoV-2 positivity rates associated with circulating 25-hydroxyvitamin D levels. PLoS ONE 15(9): e0239252.

Maghbooli Z, Sahraian MA, Ebrahimi M, Pazoki M, Kafan S, et al. (2020) Vitamin D sufficiency, a serum 25-hydroxyvitamin D at least 30 ng/mL reduced risk for adverse clinical outcomes in patients with COVID-19 infection. PLOS ONE 15(9): e0239799.

Malihi Z., Lawes C.M.M., Wu Z., Huang Y., Waayer D., Toop L., Khaw K.T., Camargo C.A., Scragg R. Monthly high-dose vitamin D supplementation does not increase kidney stone risk or serum calcium: Results from a randomized controlled trial. Am. J. Clin. Nutr. 2019;109:1578–1587. doi: 10.1093/ajcn/nqy378.

McCullough P.J., Lehrer D.S., Amend J. Daily oral dosing of vitamin D3 using 5000 TO 50,000 international units a day in long-term hospitalized patients: Insights from a seven year experience. J. Steroid Biochem. Mol. Biol. 2019;189:228–239. doi: 10.1016/j.jsbmb.2018.12.010.

Uwitonze A.M., Razzaque M.S. Role of Magnesium in Vitamin D Activation and Function. J. Am. Osteopath Assoc. 2018;118:181–189. doi: 10.7556/jaoa.2018.037.

Youssef, D. A., Miller, C. W., El-Abbassi, A. M., Cutchins, D. C., Cutchins, C., Grant, W. B., & Peiris, A. N. (2011). Antimicrobial implications of vitamin D. Dermato-endocrinology, 3(4), 220–229.


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