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Vitamin D and the Immune System

May 18, 2020

How it helps the immune system

Vitamin D plays a vital role in the function of the immune system. Many immune cells have receptors for Vitamin D. Once it binds to these receptors, Vitamin D helps certain immune cells called monocytes transform into specialized cells called macrophages that can kill bacteria and viruses. Also, metabolites of Vitamin D regulate production of proteins that can directly kill microbes and help reduce infections.


Research data shows that deficiency of Vitamin D is associated with an increased risk of respiratory infections. In addition, recent data analyses have determined that taking Vitamin D supplements can decrease the risk of acute respiratory tract infections.

Taking Vitamin D daily or weekly was found to be protective as opposed to taking the supplement less frequently and the researchers recommended taking 2000 IU of Vitamin D per day to support optimal immune function. [1] This recommendation corresponds to Endocrine Society guidelines and is within the daily tolerable upper limit for adults. [1,2]

Although there is no current scientific data proving that Vitamin D specifically protects against COVID-19, a recently published study found a possible association between low Vitamin D levels, number of COVID-19 cases, and deaths from COVID-19 in multiple European countries [3]. In addition, researchers in the Phillipines found that COVID-19 patients with higher blood Vitamin D levels had better clinical outcomes. [6]

Sources of Vitamin D

Our skin can use ultraviolet energy from the sun to make a precursor of Vitamin D that is then transformed into the active form of the vitamin in the kidneys and liver. Outside of the summer months, it is difficult for our skin to make enough Vitamin D from sun exposure if we live in northern latitudes (level of Virginia and north). Even in summer, we need to protect ourselves from skin cancer with sunscreen and this decreases our ability to make Vitamin D. Aging, air pollution and darker skin also decrease our ability to make Vitamin D.

Vitamin D can be found in eggs, beef, butter, fish and fortified foods such as milk, orange juice and cereal, but it is difficult to get adequate amounts from these sources.

Optimal blood levels

If you are thinking about supplementing with Vitamin D, it is best to talk to your doctor about getting your blood level tested. Recommendations vary, but most experts agree that optimal Vitamin D levels range between 30 to 60 ng/mL.[4,5] Knowing your blood level will help insure proper dosing and help prevent potential side effects of taking too much Vitamin D, such as high blood calcium levels and kidney stones.

For more information, check out these sources below:

1. Calder PC, et al. Nutrients. 2020 Apr 23;12(4).

2. Holick MF, et al. J Clin Endocrinol Metab 2011; 96(7): 1911-30

3. Ilie PC, et al. The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality. Aging Clin Exp Res (2020). https://doi.org/10.1007/s40520-020-01570-8

4. Grant WB, et al. Targeted 25-hydroxyvitamin D concentration measurements and vitamin D3 supplementation can have important patient and public health benefits. Eur J Clin Nutr 74, 366–376 (2020). https://doi.org/10.1038/s41430-020-0564-0

5. Gröber U, et al. “Vitamin D: Update 2013: From rickets prophylaxis to general preventive healthcare.” Dermato-endocrinology vol. 5,3 (2013): 331-47. doi:10.4161/derm.26738

6. Alipio, M Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 http://dx.doi.org/10.2139/ssrn.3571484