Vitamin D and COVID, how much proof do we need?
Vitamin D has been maligned and praised throughout 2020 and into 2021.
As a cheap supplement that nearly everyone has access to, why is it getting so much attention?
Many studies show a strong association between vitamin D deficiency and increased numbers and severity of respiratory infections. These studies show a relationship between vitamin D and COVID, not that vitamin D deficiency causes COVID. This distinction is important because a third variable may actually be responsible for the effect. Imagine studying 100 people who have double the number of respiratory infections per year compared to the baseline population. They all have low levels of vitamin D.
Vitamin D and COVID
Is having low levels of vitamin D cause their increased risk of respiratory infections?
Maybe they live in a crowded, understaffed nursing home. They do not get outside and eat a poor diet. These factors could explain the increased risk for infection and the low vitamin D levels. But you would not know that unless you were looking for it or structured your study to remove the effect of other variables that are not measured. Here are five studies that support the relationship between vitamin D deficiency and more severe respiratory diseases.
Researchers in Germany followed 9548 adults aged 50-75 for 15 years to evaluate their respiratory disease mortality. Among study participants, 44 percent had low vitamin D levels, and 15 percent were vitamin D deficient. Overall, after adjusting for sex, age, the season of blood draw, school education, BMI, physical activity, and fish consumption, 41 percent of respiratory disease mortality was statistically because of low vitamin D levels.
A meta-analysis published in the British Medical Journal in 2017 reviewed 25 randomized, double-blind, controlled trials that had 11,321 participants. Vitamin D supplements reduced each individual’s risk by at least one respiratory infection. When all the results were averaged together, there was a slight protective effect. While daily and weekly doses of vitamin D reduced risk, single large doses of vitamin D did not. Protective effects of vitamin D were greatest in those with the lowest vitamin D levels.
In a retrospective study in 2020, Quest Diagnostics in the U.S. looked at the labs for vitamin D levels and SARS-CoV-2 positivity for 191,779 de-identified participants. The authors found a strong inverse relationship between vitamin D levels and SARS positivity that persisted across latitudes, races/ethnicities., sexes, and age ranges. They found the risk of being positive for SARS-CoV-2 was 1.6% lower with each vitamin D increase by 1 ng/ml. A previous study showed that for every 4ng/ml increase in vitamin D, there was a 7% decrease in risk for seasonal respiratory infections.
When researchers at the University of Chicago Medicine reviewed the health records of 489 patients who had vitamin D testing within the previous year, they found that the relative risk for testing positive for COVID was 1.77 times greater for vitamin D deficient patients when compared to those who were not. Two-thirds of the study participants were non-white, and 47 percent had a BMI greater than or equal to 30 (obese). Though the results were significant, the authors point out that this was a retrospective study. There may be unknown confounding variables that increase the risk for both vitamin D deficiency and COVID.
So what is my recommendation for taking Vitamin D?
The best thing to do is check with your doctor to see if you might have low vitamin D, and if it is low, you’ll def need to get more vitamin D, especially during the winter months.
The common question is, How much Vitamin D should I take a day?
Personally, I take 1,000 IU per day. I know that I’m not going to run anywhere near toxic levels of vitamin D with that dose, while at the same time, I know that I won’t be vitamin D deficient.
Doctor Mike Hansen, MD
Internal Medicine | Pulmonary Disease | Critical Care Medicine
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