Preliminary findings from a yet-to-be-peer-reviewed study from the UK's Queen Elizabeth Hospital Foundation Trust and the University of East Anglia indicate that a vitamin D deficiency may be associated with a higher mortality in Covid-19 patients. The association has brought into question whether or not it’s advisable for people in countries associated with lower levels of vitamin D to take supplements as a precaution.

Vitamin D is produced by our skin cells when we are exposed to the Sun and is needed to regulate the amount of calcium and phosphate in the body. We can also absorb vitamin D from foods such as fish and mushrooms, and the nutrients it provides are needed to keep bones, teeth, and muscles healthy. A significant deficiency of vitamin D can lead to rickets and osteomalacia. There’s also emerging evidence of the vitamin's role in the immune system, as low levels have been associated with autoimmune conditions. The new preliminary study has also linked a deficiency of vitamin D with mortality rates for Covid-19 in countries across Europe.

The connection was made following a review of existing data on the average levels of vitamin D among the citizens of 20 countries across Europe. This data was then compared to the mortality rates from Covid-19 in the same 20 countries. A statistical analysis of the figures revealed a significant correlation between the figures, with the areas suffering the highest mortality rates from Covid-19 also being among the lowest average concentrations of vitamin D in the general population.

"The most vulnerable group of population for Covid-19 is also the one that has the most deficit in vitamin D," the researchers conclude in their preliminary report.

The UK's National Health Service (NHS) currently suggests taking a daily vitamin D supplement to keep your bones and muscles healthy. "This is because you may not be getting enough vitamin D from sunlight if you’re indoors most of the day," it says on the website, though it adds there is no evidence that vitamin D reduces risk of coronavirus, and to not buy more than you may need. 

However, experts warn it’s not yet time to make a dash for the vitamin aisle. Such cross-sectional reports must be considered with care, as they only consider one variable and as such it’s false to confuse correlation with causation. Areas with higher vitamin D levels might be benefiting from some other physiological benefit that is lowering their mortality risk from Covid-19, which would make taking supplements both ineffective and could potentially lead to other health issues due to unnecessary supplementation. 

However, if they pass peer review the findings could certainly suggest that vitamin D is a worthy area of investigation for identifying lifestyle factors that could improve or worsen the degree of disease experienced. Vitamin D has previously been associated with preferable outcomes surrounding respiratory illnesses such as influenza and tuberculosis.