COVID-19 and Vitamin D

Vitamin D is a fat-soluble hormone that we naturally synthesize from cholesterol in sun-exposed skin. There are no food sources that can provide an adequate supply, though irradiated dairy products, fatty fish, eggs and beef liver do have some (but not in sufficient quantities). Most Vitamin D-deficient people respond well to oral supplementation, although some people can have difficulty absorbing it, and some obese patients have a very difficult time getting their levels up with standard doses. The studies on Vitamin D supplementation seem to offer contradictory results, and I don't have the time to get into the the various reasons for this. However, I will say that most of the negative studies (ones showing no benefit from Vitamin D supplementation) have common methodological errors, not least among them that they did not administer it in a manner anywhere near how Integrative Practitioners actually prescribe. Despite this confusion, it is known that Vitamin D has immunomodulatory effects and that adequate levels reduce the incidence of respiratory infections and help the immune system fight viral infections at various stages of infection (1).

Since the pandemic is new, published, peer-reviewed research on Vitamin D and SARS-CoV-2 infection is lacking. However, there are some studies in pre-print that are interesting to consider (caveat: during this pandemic we have learned the hard way about accepting these pre-print studies at face value). One study out of Chicago linked those who were expected to have low Vitamin D levels (based on previous Vitamin D measurement and/or lack of supplementation) with a 77% greater risk of testing positive for SARS-CoV-2 than those with known or presumed adequate levels of Vitamin D (2). Another study in Israel actually measured Vitamin D levels and found that those with insufficient amounts (<30 ng/mL) were 45% more likely to test positive for infection and 95% more likely to be hospitalized with COVID-19 (3). The results were even more impressive when looking at levels of Vitamin D <20ng/mL. A small study in New Orleans demonstrated that people admitted to the ICU with COVID-19 were more likely to have low levels of Vitamin D than those admitted to the hospital but not requiring ICU management. The authors pointed out that people who have been particularly at risk for the worst outcomes with COVID-19 are often the elderly, black people, diabetics and people with hypertension are known to be more likely to have low levels of Vitamin D (4). A more recent analysis in northeastern England (where Vitamin D deficiency is common) has similar findings (5). One hospital in Singapore took this evidence to heart and treated patients admitted with COVID-19 with a combination of Vitamin D, magnesium (needed to activate Vitamin D in many functions), and Vitamin B12 (to promote a healthy gut microbiome). Only 18% of the treated patients required oxygen supplementation or ICU management, compared to 62% of those who were not treated (6) (some of the weaknesses of this study are that they did not measure Vitamin D levels before treatment and it was small cohort comparison, not randomized).

Since we have left our scantily clad, hunter-gatherer ways and many of us no longer live at the equator, Vitamin D deficiency is common. Vitamin D supplementation is generally regarded as safe (although very high doses can precipitate kidney stones). Given the potential benefit of adequate levels in safely surviving COVID-19, it is not unreasonable to have your levels checked. I consider levels <30 ng/mL to be deficient (some set that level at 20 ng/mL) and levels 40-80 ng/mL to be ideal. One can get this tested at your primary care physician's office. Some insurances don't cover the cost except for certain medical conditions, but the test is usually in the $50 - $80 range. If you are fair-skinned and spend time regularly outdoors, you are probably OK during the summer months. I encourage my Wisconsin patients to supplement with 1000 IU daily during the 6 months of darkness and cold we experience, and my black patients likely need to take a supplement year-round (a recent study called this into question, but I haven't reviewed it yet). It is best absorbed when taken with food and I prefer the capsule form to tablets since fat helps with absorption.

1. https://pubmed.ncbi.nlm.nih.gov/21736791/

2. https://www.medrxiv.org/content/10.1101/2020.05.08.20095893v1

3. https://www.medrxiv.org/content/10.1101/2020.07.01.20144329v1.full.pdf

4. https://www.medrxiv.org/content/10.1101/2020.04.24.20075838v1

5. https://onlinelibrary.wiley.com/doi/abs/10.1111/cen.14276

6. https://www.medrxiv.org/content/10.1101/2020.06.01.20112334v2