Provider Practice Essentials registered nurse continuing education

The Neglected Benefits of Vitamin D

Lindee Abe, ARNP

Vitamin D is back! In the beginning of the 20th century, it was not uncommon for patients with infectious diseases (like influenza and tuberculosis) to be placed outside. One rationale for this is that the fresh air created a natural ventilation system that decreased the spread of the infectious disease particles. While this is true, there is another factor that contributed to the recovery of these patients. Sunlight from the outdoors provided the patients with Vitamin D, which can also help with the patients’ immune response to illness. We now use indoor hospitals that help us contain infection, house appropriate equipment, and control environmental. Perhaps we have neglected the importance of sunlight in the healing process and immune response our body need in order to fight infection.


So what is Vitamin D?


There are two forms of Vitamin D: D2 and D3. D2 is the form that is absorbed from UVB exposure and D3 is found through diet. Vitamin D supplementation comes in both D2 and D3. Both forms of vitamin D are effective. The body can convert these forms into active vitamin D. Vitamin D is also unique in that it is the only vitamin that is a hormone as well. It is absorbed by the body and then synthesized into its active form. Calcitriol is the the active form of vitamin D. This factors into the ability to test for vitamin D, but more on that later.

Vitamin D plays a role in bone health. It wasn’t until recently that there has been more literature indicating the importance of Vitamin D in immune health. Vitamin D is found on immune cell receptors – specifically antigen-presenting cells, B cells, and T cells. It is also found in intestinal cells. Here, it plays a role in promoting normal gut flora and a healthy microbiome.

Vitamin D Conversion Pathway

How do we know that it affects immunity?

This is more difficult to answer. We have studies that show a relationship between autoimmune disease and low vitamin D levels. Associations have been found between vitamin D deficiency and diabetes mellitus type 1, multiple sclerosis, systematic sclerosis, inflammatory bowel disease, and rheumatoid arthritis. This is in addition to systemic lupus, that not only showed increased incidence of disease, but also an association between lower levels of vitamin D and high incidence of flares of the disease.

There is evidence of increased risk of infection, specifically tuberculosis, in patients with low vitamin D levels. As much as a 5 fold increase in risk between latent tuberculosis and progression to active tuberculosis has been found in those with low levels of Vitamin D. There have also been theories that low levels of vitamin D have a role in the increased incidence of tuberculosis in the winter months when vitamin D exposure is at its lowest.


How do we test for it


Vitamin D is measured by laboratory testing – specifically the 25-hyroxyvitamin D laboratory test. There are two tests for vitamin D, the 25-hydroxyvitamin D and the 1,25- hydroxyvitamin D. These measure two different forms of vitamin D, inactive and the active hormone. The preferred test for vitamin D is the 25-hydroxyvitamin D, which test the inactive form of vitamin D, because the inactive form has a longer half-life.

The Endocrine Society has established guidelines that below 20 ng/mL should be considered deficient, between 20-29 ng/mL insufficient, and greater than 30 ng/mL is sufficient. However, the optimal Vitamin D levels seem to vary by different organizations. The Vitamin D Council also recommends levels between 50 to 80 ng/mL. When reviewing the varying opinions, the most frequent goal vitamin D level is between 30 to 50 ng/mL.

What dose of vitamin D is appropriate?

The next question is how much Vitamin D should healthcare providers be recommending? As one would suspect, there are many different answers. Vitamin D toxicity has been noted to occur at the injection of greater than 10,000 iu of Vitamin D a day, but some organizations theorize that it is actually closer to above 60,000 iu per day. It is recommended to stay below 10,000 units per day for adults to follow the Endocrine Society’s guidelines. The most common initial treatment for Vitamin D deficiency is with a 50,000 iu dose per week for 6-8 weeks and then 1,000-2,000 iu per day. It should also be noted that persons can consume too much vitamin D. Hypervitaminosis D can lead to hypercalcemia in some patients.

Vitamin D and COVID-19


The question that we have seen arise over the past year is what role vitamin D has with COVID-19. The medical community has been desperately searching for treatments and ways to reduce risk of complications with this pandemic. There have been several article that have reviewed vitamin D and COVID-19, but in the end it has been more of a hypothesis than a proven relationship. That is until a recent study from the University of Chicago and Medicine. The University of Chicago and Medicine study was a retrospective study that showed persons with vitamin D levels that were above 40 ng/mL were less likely to contract Covid-19. This was especially true for Black patients that would also have more difficulty with synthesizing vitamin D from sun exposure. This study also may provide insight into why minorities have been noted to be more at risk for COVID-19.


There is much more research to be done regarding vitamin D and COVID-19 as we continue to learn more about this virus. While vitamin D levels aren’t a cure for COVID-19, it can be modifiable factor that providers can address as a preventative strategy for COVID-19 and respiratory illness in general. Dr. Fauci even recommended vitamin D supplementation for immune health and takes vitamin D himself to help keep himself healthy.

Would I recommend supplementation to everyone?

I’m not sure that supplementation is necessary for every person. Will I consider it as part of a comprehensive approach to better health? Of course. I will continue to use this in open dialogue with patients and consider it as an additional test that could be ordered if vitamin D deficiency is suspected. While more research is likely to come out regarding vitamin D and COVID I will continue to look read and make sure to share my findings with patients and colleagues. I am sure that in the coming months, there will be more research available regarding a potential relationship between vitamin D and COVID-19.

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Caldwell, A. Study suggest high vitamin D levels may protect against COVID-19, especially for
Black people. Retrieved from https://www.uchicagomedicine.org/forefront/coronavirus-diseasecovid-19/vitamin-d-covid-study.

Martens, P., et al. Vitamin D’s Effect on Immune Function. Nutrients 2020, 12, 1248.
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Holick, M.,et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine
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Singh, S., & Gambert, S. (2014). VITAMIN D Health Practitioner’s Guide to Prescribing
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Talat, N., et al. (2010). Vitamin d deficiency and tuberculosis progression. Emerging infectious
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