Vitamin D: Evidence, Speculation, and COVID-19

As we struggle with this pandemic, cheap answers have great appeal. Some are absurd, like bleach for purposes other than cleaning. Others present a puzzle with many dimensions to resolve. Such is the case of vitamin D. This week three authoritative health groups in England sorted through all the evidence on vitamin D and COVID-19. Their conclusion presents a mixed message. People should follow standing advice to take modest doses (400 I.U. per day) of vitamin D for bone and muscle health in fall and winter months. But current evidence does not support taking larger doses to prevent or treat COVID-19.

Absence of Proof

Right now, we have an abundance of pre-print studies about vitamin D and COVID-19. Because they are pre-prints, lacking the benefit of peer review, they come with a grain of salt. And the findings vary wildly.

British authorities conducted and published not one, but two evidence reviews on vitamin D. Public Health England launched a review by the Scientific Advisory Commission on Nutrition (SACN). At about the same time, the National Institute for Health and Care Excellence (NICE) conducted a related evidence review. They landed on more or less the same conclusions, summarized here by NICE:

“The expert panel supported current government advice for everyone to take the supplement throughout the autumn and winter, however the panel concluded that there is currently not enough evidence to support taking vitamin D solely to prevent or treat COVID-19.”

Of course, absence of proof is not proof of absence. All of these organizations endorsed the need for more and better research to resolve the open question. Can vitamin D either prevent or help in the treatment of COVID-19? The current evidence is not adequate to resolve ongoing speculation.

Vitamin D and Respiratory Infections

SACN focused its report on the overlapping question of vitamin D and respiratory infections. This is where we see a flood of testimonials. I’ve been taking vitamin D for years and I never get colds or flu anymore! This is the form they follow. But data is not the plural of anecdote. The conclusions of SACN were cautious:

“Evidence considered in this update suggests, overall, that there may be some benefit from daily, low-dose vitamin D supplementation (between 10 and 25 µg/day; 400 to 1000 IU/day) in reducing risk of acute respiratory tract infections (ARTI). The size of any potential benefit of vitamin D in reducing ARTI risk may be small.”

Separating Speculation from Facts

The passion of the vitamin D fan club is striking. However, neither passion nor speculation should be a substitute for facts. Right now, the facts tell us that the reason to take a vitamin D supplement is to protect our muscles and bones. Any thought that it will help with COVID-19 is speculation, and taking too much would be quite unwise.

Click here for the NICE report and here for the SACN report. For further perspective, click here, here, and here.

Vitamin D on Wood, photograph © Ted Kyle / flickr

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December 20, 2020