There are multiple studies showing a link between vitamin D deficiency and severe COVID-19. But whether (extra) vitamin D can also help prevent you from becoming seriously ill from the corona virus, we do not know yet.

Vitamin D is produced when you walk outside in the sun and you can also get it through food or extra vitamin pills. Relatively early on in the corona crisis, vitamin D deficiency was suggested as one of the possible reasons that some people only get a mild cold from the corona virus, while others become seriously ill. What do we know now?

What is vitamin D good for?

Vitamin D is important for, among other things, the maintenance of strong bones and teeth, muscle strength and plays a role in the immune system. Children up to four years old, the elderly and anyone with a tinted or dark skin color are recommended by the Nutrition Center to take extra vitamin D.

Renate de Jongh, internist-endocrinologist at the Amsterdam UMC, is conducting research into the function of vitamin D. She says that we do not yet know whether taking vitamin D reduces the risk of becoming seriously ill due to the corona virus.

Vitamin D lowers the risk of respiratory infections We do know that taking vitamin D pills daily or weekly, especially in people who have a shortage of them, slightly reduces the risk of respiratory infections. This emerged from an analysis of 25 well-conducted studies.

De Jongh explains that this is probably because vitamin D in the lungs enhances the production of antibodies against viruses and bacteria. Sufficient vitamin D thus helps the lungs to be better prepared against intruders.

Although we do not yet know whether vitamin D helps against corona, according to de Jongh it does not hurt to take vitamin D, especially in winter.

"There is a kind of optimal amount. So more is not necessarily better. If you take enormous amounts of vitamin D, it can even be bad for your health. But a little extra vitamin D has no adverse effects."

What about the studies that found a link? Why don't we really know whether vitamin D helps against corona? Several studies did find indications that the number of people with a vitamin D deficiency in a country is related to the number of hospital admissions and deaths as a result of COVID-19. In some studies, people with a vitamin D deficiency are also more likely to have a severe COVID-19 infection than those without deficiency.

De Jongh emphasizes that these types of studies do not tell whether vitamin D deficiency is also the cause of severe COVID-19. "We know, for example, that obese people, people with respiratory diseases such as asthma and COPD, and the elderly are often deficient in vitamin D." These are groups that are also relatively at risk for severe COVID-19. But whether this is due to a lack of vitamin D or other underlying causes, we do not know.

To answer this question, according to De Jongh, you need studies in which some of the participants take extra vitamin D and some of the participants take a pill without any active ingredients, a placebo. Differences between these groups can probably tell you something. "These kinds of studies with placebos are now being done in several places around the world, we just don't have results yet."