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COVID Prevention 102: Immune Boosting through Vitamin D

Updated: Jun 20, 2023

Vitamin D and immunity

In my first article on COVID prevention, I briefly reviewed the importance of the microbiome in preventing infections and boosting immunity to COVID. Another important factor to our immunity is vitamin D levels and the literature shows that those who are vitamin D deficient are experiencing more COVID associated complications.

Vitamin D is more of a hormone than a vitamin, which is produced in the skin by exposure to sunlight. It has multiple functions, most importantly around calcium absorption, regulation, and keeping bones strong. It has now become clear that vitamin D also plays a role in immune function and decreases infection and death. There are several functions of vitamin D including adaptive immunity, improving physical barriers, cellular natural immunity, and anti-oxidation activity. Vitamin D reduces viral replication rates, decreases pro-inflammatory cytokine concentrations, and increases anti-inflammatory cytokines. The pro-inflammatory cytokines are what cause “cytokine storm” in COVID patients, which many of us here about in the media.

Symptoms of vitamin D deficiency are vague in adults, some include fatigue, bone pain, muscle cramps, muscle weakness, and mood changes like depression. Vitamin D levels are lower in some because of aging and/or darker colored skin. Most people are indoors, especially in the winter months, and long periods of time without exposure to sun prevents vitamin D production. Sunscreen also contributes to low vitamin D production, but over exposure to the sun can cause skin cancer.

The best way to test vitamin D levels, is to do a blood test looking for 25-hydroxyvitamin D, or also known as 25(OH)D. Optimal levels vary by age, check with your health care provider to get the test and understand your optimal level. Eating foods high in vitamin D is one way to increase vitamin D levels, but often doesn’t help a person reach optimal levels. Foods that have high vitamin D include cod liver oil, swordfish, salmon, tuna, milk, yogurt, cheese, egg yolks, liver, and sardines. Getting sun exposure is another way to produce more vitamin D, but exposure time varies by the color of your skin. Generally, exposing the back, arms, legs, and face to the sun for 10-15 minutes three times a week will help most people. Darker skinned and older people will need slightly more time in the sun.

The most efficient way to get vitamin D, is through supplementation. Vitamin D3 is available over the counter and it is very difficult to overdose on vitamin D. It is highly recommended to work with a health professional to test, understand your level, and how to reach optimal levels. Vitamin K metabolism also may play a part in lung damage and thromboembolism, and deficiency in vitamin K could be a factor in making COVID worse. Yet, more research is needed in this area. It is known that vitamin D and vitamin K work synergistically and found to occur together naturally in many foods. Many integrative/functional medicine providers prescribe both together, though no formal recommendations have been made for vitamin K to be given with vitamin D. Vitamin K2 tends to be more deficient than vitamin K1, and many supplements offer both vitamin D3 and vitamin K2 together in liquid and pill form. Magnesium also activates Vitamin D through enzyme reactions in the liver and kidneys. Magnesium supplementation is recommended with vitamin D deficiency, again please consult your health provider to get appropriate dosing.

Simply improving your vitamin D levels can be a powerful immune booster in fighting COVID. For more information on testing Vitamin D levels and getting pharmaceutical grade vitamin D, vitamin K, and magnesium at an appropriate dose, please contact us at


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.

Janssen, R., Visser, M., Dofferhoff, A., Vermeer, C., Janssens, W., & Walk, J. (2020). Vitamin K metabolism as the potential missing link between lung damage and thromboembolism in Coronavirus disease 2019. British Journal of Nutrition, 1-8. doi:10.1017/S0007114520003979

McCall, B. (December 11, 2020). Vitamin D Deficiency in COVID-19 Quadrupled Death Rate.

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