As evidence builds that COVID-19 patients with vitamin D deficiency are much more likely to experience severe clinical outcomes (ICU risk is 20-fold greater, international data suggests), urgent trials in Europe and North American are underway to evaluate whether vitamin D could be used to treat or prevent the disease. 

In early, April two studies by researchers in Ireland drew international attention by highlighting vitamin D’s potential role in priming the body’s defences against COVID-19. The Irish researchers, part of the TILDA study group, described vitamin D “as a potent immune modifying micronutrient” and suggested that, at sufficient levels, it could play an important role in protecting vulnerable adults, particularly those who are obese and those with pre-existing lung conditions – both groups among those known to be more susceptible to complications from COVID-19. 

Findings in Europe and North America that black and Asian minority ethnic (BAME) groups are disproportionately affected by COVID-19, and more likely to die from it, raised further questions about vitamin D’s role. While socio-economic factors are likely to contribute to this, there is mounting concern that poorer absorption of vitamin D from sunlight in people with darker skin may be playing an important role. 

Similarly, elderly and other institutionalised groups may be more susceptible to serious complications from COVID-19 due to poor vitamin D status. The problem is likely to have been compounded by the lockdown itself, which may have shifted larger parts of the population – who have spent weeks indoors – to an at-risk status. 

While the high death rates seen in Italy and Spain might seem to weaken the logic beyond the vitamin D-COVID-19 outcome connection, vitamin D awareness and supplementation are low in southern Europe (in contrast to, say, Nordic countries where vitamin D supplementation and fortification is common, or even mandated, and where death rates have been much lower). 

Urgent studies into the effect of vitamin D status on COVID-19 outcomes are now being carried out in France, Spain and the United States. 

One striking study carried out earlier this year in the Philippines examined vitamin D status, and hospitalisation outcomes in 212 COVID-19 patients. Lead researcher, Mark Alipio, observed: “Vitamin D status is significantly associated with clinical outcomes (p<0.001). For each standard deviation increase in serum 25(OH)D, the odds of having a mild clinical outcome rather than a critical outcome were increased approximately 19.61 times.”

“Human nature is such that simple solutions to complex issues, for example vitamin C for scurvy, and hand washing prior to baby delivery, are often not readily embraced”

The study also showed that of nine patients with mild clinical outcomes, 47 had ‘normal’ vitamin D levels. Conversely, only two of the 48 critical patients had ‘normal’ vitamin D levels.

In late April a group of 25 International researchers were joint signatories to a letter to the BMJ on this subject, written by US expert Robert A Brown, chair of the McCarrison Society. Brown – who, in a paper from earlier this year, “hypothesised that vitamin D deficiency may significantly compromise, respiratory immune response function, thus greatly increasing risk of COVID-19 hospitalisation, severity and mortality” – calls for urgent new research to be carried out into vitamin D status and COVID-19 outcomes.

Brown also warns against dismissing “simple solutions to complex issues”. He writes: “Human nature is such that simple solutions to complex issues, for example vitamin C for scurvy, and hand washing prior to baby delivery, are often not readily embraced; but surely the scale and impact of the COVID-19 pandemic demands all avenues are fully explored; more so when no other effective treatment strategies as yet exist. A safe simple step, the correction of a deficiency state, vitamin D this time, convincingly holds out a potential, significant, feasible COVID-19 mitigation remedy”.