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Vitamin D and COVID: what’s the link?

Last updated: Oct 27, 2021
6 min read


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

We all know the importance of vitamin D for maintaining healthy bones and strong teeth, but researchers have been investigating a new potential use for the vitamin: COVID-19 prevention and treatment. Does this theory hold any water? Let’s dig in.


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Vitamin D and COVID-19

When the pandemic hit, researchers were eager to study vitamin D for its potentially preventative and therapeutic benefits. Vitamin D is cheap, accessible, and easy-to-take, so it’s an attractive option that could have a massive public health impact—if it actually works, that is. 

Why did researchers even start looking at vitamin D for this purpose to begin with? Aside from boosting the immune system, vitamin D may also have anti-inflammatory properties—important since inflammation is responsible for some of the severe COVID-19 symptoms (Murai, 2021). 

Several observational studies looking at the role of vitamin D and COVID-19 prevention have shown mixed results. One review analyzing ten studies found that people with low vitamin D levels were at higher risk of contracting COVID-19 (Liu, 2021). Other studies have not shown an association (Lordan, 2021).

Vitamin D is also being investigated as a potential treatment for COVID-19. One study gave a type of vitamin D called calcifediol to 50 hospitalized COVID-19 patients. They found that the people who received vitamin D were less likely to be admitted to the intensive care unit (ICU) than the 26 COVID-19 patients who did not receive calcifediol. However, more people had diabetes and high blood pressure in the group that did not receive vitamin D, which may have affected the results, since diabetes and high blood pressure increase a person’s risk for severe consequences of COVID-19 (Entrenas Castillo, 2020). Another clinical trial looked at 240 hospitalized COVID-19 patients and found that giving a one-time, high-dose vitamin D treatment did not reduce hospital length of stay, ICU admission, the need for ventilation, or death compared to the patients that did not receive vitamin D (Murai, 2021). 

The jury is still out on vitamin D for COVID-19, but researchers haven’t given up hope that there may be something there. Larger, randomized controlled trials are ongoing to assess the potential benefit of vitamin D for COVID-19. As of now, there is no clear evidence that vitamin D can prevent you from getting sick or treat you if you are ill. Focusing on proven strategies, such as receiving the COVID-19 vaccine, is your best bet to keep yourself and others safe. 

What is vitamin D?

Vitamin D is a nutrient our bodies use to grow and function properly. When exposed to the sun, our skin makes vitamin D, but we can also get this nutrient from foods and supplements. Most people associate vitamin D with bone health since it helps our bodies absorb calcium—a main component of bones. But vitamin D receptors are present on most cell types in the body, so its role goes well beyond keeping our bones strong (Lordan, 2021). 

Vitamin D and immune function

Adequate vitamin D levels help the immune system fight off infections. One way is by increasing the body’s production of natural antimicrobial substances that can help kill foreign invaders like bacteria and viruses (Aranow, 2011). 

A 2017 meta-analysis evaluated whether or not vitamin D supplementation could decrease the risk of developing acute respiratory tract infections. The results showed that vitamin D was protective, especially in people with severe vitamin D deficiency (Martineau, 2017). 

The results of this study lead scientists to wonder what impact vitamin D might have on the prevention or treatment of other infectious diseases—hence, their investigation into the relationship between vitamin D and COVID-19. 

Healthy levels of vitamin D

While the effects of vitamin D for COVID-19 remain unknown, there is one thing that’s clear: Maintaining a healthy nutritional status—including having good vitamin D levels—is linked to better immune function and overall health. But how much do you need? 

The National Academy of Medicine (previously the Institute of Medicine) has established Recommended Dietary Allowances (RDAs) for vitamin D—the average daily intake needed to maintain levels in healthy individuals. 

While some people can get enough sunlight to meet their daily vitamin D needs, most of us probably don’t fall into that category. The NAM’s recommendations assume people receive limited sun exposure and that all vitamin D comes from the diet. The RDA for people 1–70 years old is 600 IU (15 mcg), while individuals over 70 should get 800 IU (20 mcg) of vitamin D daily (Ramasamy, 2020). 

Certain people are at an increased risk of vitamin D deficiency and may require supplementation to maintain adequate levels. Risk factors include: (NIH, 2021; Ramasamy, 2020)

  • Breastfed infants, as vitamin D doesn’t travel into breastmilk well
  • People with chronic kidney disease 
  • Long-term use of certain seizure medications, including phenobarbital, carbamazepine, phenytoin, and valproate 
  • People with obesity or those who’ve undergone gastric bypass surgery 
  • Older adults 
  • People with conditions that affect fat absorption, such as cystic fibrosis, celiac disease, Crohn’s disease, ulcerative colitis, and certain forms of liver disease 
  • People with limited sun exposure 

How to get enough vitamin D

Most people in the United States don’t get the recommended amount of vitamin D (NIH, 2021). Here’s how the sun, foods, and supplements can help increase your levels. 

Sun exposure 

When UVB (ultraviolet B) rays from the sun come into contact with your skin, your body produces vitamin D. While some people may get the majority of their vitamin D through this process, several factors make it difficult to rely on the sun. Older age, darker skin color, the season, time of day, and the use of sunscreen can all affect vitamin D production (NIH, 2021). 

Since UV exposure is the most preventable cause of skin cancer, limiting your time in the sun is important for reducing your risk, which is why most of us need additional sources of vitamin D (NIH, 2021). 

Food sources

Only a few foods naturally contain vitamin D. These include fatty fish like trout, salmon, tuna, and sardines, cod liver oil, egg yolks, and mushrooms. Most people consume most of their dietary vitamin D through fortified foods—foods that have vitamin D added—such as milk (both dairy and plant-based products), cereal, and certain yogurts and orange juice. One cup of milk typically has at least 120 IU (3 mcg) of vitamin D added, which is about 15–20% of the recommended daily intake, depending on your age (NIH, 2021). 

Dietary supplements

Your healthcare provider may recommend a vitamin D supplement to help you meet your nutritional goals. Vitamin D supplements come in two forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). While both effectively raise vitamin D levels, most studies suggest that vitamin D3 increases levels to a greater extent and for longer than vitamin D2 (NIH, 2021).  

Typical dosing ranges from 600 to 1000 IU (15–25 mcg) per day, although your doctor may recommend higher dosing depending on your situation. 

At the start of the pandemic, sales of supplements and natural products skyrocketed as people attempted to boost their immune system and protect themselves from the coronavirus. Unfortunately, companies seized this opportunity and began promoting various products—including vitamin D—with unproven claims of COVID-19 protection (Lordan, 2021). While we can’t depend on any of these products to protect us from COVID-19 infection, maintaining a healthy diet and nutritional status improves overall health. Let your healthcare provider know if you’re concerned about your vitamin D status. They may suggest a blood test to check your levels and recommend a vitamin D supplement if needed. 


  1. Aranow, C. (2011). Vitamin D and the immune system. Journal of Investigative Medicine: The Official Publication of the American Federation for Clinical Research, 59(6), 881–886. doi: 10.2310/JIM.0b013e31821b8755. Retrieved from 
  2. Entrenas Castillo, M., Entrenas Costa, L. M., Vaquero Barrios, J. M., Alcalá Díaz, J. F., López Miranda, J., Bouillon, R., et al. (2020). Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study. The Journal of Steroid Biochemistry and Molecular Biology, 203, 105751. doi: 10.1016/j.jsbmb.2020.10575. Retrieved from 
  3. Liu, N., Sun, J., Wang, X., Zhang, T., Zhao, M., & Li, H. (2021). Low vitamin D status is associated with coronavirus disease 2019 outcomes: a systematic review and meta-analysis. International Journal of Infectious Diseases : IJID: Official Publication of the International Society for Infectious Diseases, 104, 58–64. doi: 10.1016/j.ijid.2020.12.077. Retrieved from 
  4. Lordan, R. (2021). Notable developments for vitamin D amid the COVID-19 pandemic, but caution warranted overall: a narrative review. Nutrients, 13(3), 740. doi: 10.3390/nu13030740. Retrieved from 
  5. Martineau, A. R., Jolliffe, D. A., Hooper, R. L., Greenberg, L., Aloia, J. F., Bergman, P., et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ (Clinical research ed.), 356, i6583. doi: 10.1136/bmj.i6583. Retrieved from 
  6. Murai, I. H., Fernandes, A. L., Sales, L. P., Pinto, A. J., Goessler, K. F., Duran, C., et al. (2021). Effect of a single high dose of vitamin D3 on hospital length of stay in patients with moderate to severe COVID-19: a randomized clinical trial. JAMA, 325(11), 1053–1060. doi: 10.1001/jama.2020.26848. Retrieved from 
  7. National Institutes of Health (NIH). (2021, August). Vitamin D: fact sheet for health professionals. Retrieved on Oct 15, 2021 from 
  8. Ramasamy, I. (2020). Vitamin D metabolism and guidelines for vitamin D supplementation. The Clinical biochemist. Reviews, 41(3), 103–126. doi: 10.33176/AACB-20-00006. Retrieved from 

Dr. Steve Silvestro is a board-certified pediatrician and Senior Manager, Medical Content & Education at Ro.