Covid-19 and Vitamin D Deficiency - Is There a Link?

Academic studies find a correlation between the severity of Covid-19 infection and vitamin D levels

Photo by Erik Mclean on Unsplash
Patient studies in The Philippines and Indonesia, and a longitudinal study in Ireland have found a correlation between the severity of Covid-19 infection and levels of vitamin D.

The problem is that, while there are plausible theories why adequate vitamin D levels might protect patients, there is no provable link.

The Philippines and Indonesian studies made actual measurements of vitamin D levels in patients who had the Covid-19 infection and found that severe levels of infection were often accompanied by low vitamin D levels.

The Irish research found correlations between the severity of Covid-19 infection and vitamin D levels in various European countries.

It should emphasized that papers that describe the first two studies are only pre-publications, not having been peer-reviewed at the time of writing. In contrast, the paper on the longitudinal study was published in the Irish Medical Journal in May.

Vitamin D levels and Covid-19 deaths in Europe

The Irish study was conducted by Dr. Eamon Laird and Professor Rose Anne Kenny, School of Medicine, with Professor Jon Rhodes at University of Liverpool. They found relatively low levels of vitamin D in northern Italy and Spain, where the Covid-19 outbreak has been particularly devastating. While in Scandinavian countries, where the severity appears to be lower, vitamin D levels were higher.

Vitamin D is found in some foods but mostly it is produced in the skin through exposure to the Sun, so this finding may seem counter-intuitive, as Spain and Italy enjoy higher levels of sunlight than the more northern countries. 

But it is precisely because of this lack of sunlight that vitamin supplements and food fortification are more common in the Nordic countries. Consequently, vitamin D levels these populations are actually higher than in the south.

The authors suggest that healthy levels of vitamin D might reduce serious Covid-19 complications but are not suggesting that it will prevent the disease. 

Vitamin D is important in regulation and suppression of the inflammatory cytokine response, the ‘acute respiratory distress syndrome’ that is the cause of death in many Covid-19 cases, so this could be a possible mechanism by which the most severe symptoms are reduced.

Vitamin D and the severity of Covid-19

The studies from the Philippines and Indonesia looked at actual cases of Covid-19 and examined the severity of the disease in patients with their observed levels of vitamin D.

Both studies found strong correlations between the clinical outcomes and vitamin D insufficiency or deficiency with severe symptoms and death being associated with the poorer levels of vitamin D.

But correlation is not causation.

The most at risk groups from the pandemic are the old and those with underlying health problems. And it is precisely these groups who are likely to suffer more from vitamin D deficiency. So it may not be a surprise that they found this correlation - older people have lower levels of vitamin D and are also more susceptible to disease but the two things may not be connected.

It also seems that people of color are more likely to become severely ill compared to those with lighter skin. 

Again, this could make sense as people with paler skin can produce more vitamin D the darker-skinned population. This could be significant in northern climes where there is less sunlight and vitamin D supplementation is not normal. But, again, it could be coincidence.


This is currently all speculative. No randomized tests have been carried out and no explanatory theory has been proved. There may well be another explanation.

Get more sunshine?

The authors of the Irish paper are calling on government to support the use vitamin D supplements. This may be a reasonable precaution as, while vitamin supplements are not thought to be particularly useful to healthy individuals under normal circumstances, they do not appear to be harmful either.

On the other hand, topping up your vitamin D levels with a little more fresh air and sunshine can’t be a bad idea either, can it?


E. Laird, J. Rhodes and R.A.Kenny, Vitamin D and Inflammation: Potential implications for the Severity of Covid-19, Irish Medical Journal, May 2020.

Raharusun, Prabowo and Priambada, Sadiah and Budiarti, Cahni and Agung, Erdie and Budi, Cipta, Patterns of COVID-19 Mortality and Vitamin D: An Indonesian Study (April 26, 2020). Available at SSRN:

Alipio, Mark, Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 (COVID-19) (April 9, 2020). Available at SSRN: or


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