As worldwide coronavirus cases continue to rise, could having sufficient levels of vitamin D protect you from the virus?
As we enter the winter months in the Northern hemisphere, a resurgence of new coronavirus cases can be seen in countries across Europe. Some European nations are even exhibiting higher cases in October than they did at the start of the pandemic in the spring. In light of this we ask whether keeping our vitamin D levels up should be a priority as winter approaches.
Vitamin D deficiency has been a proposed risk factor for COVID-19 almost since the pandemic’s start. Vitamin D deficiency is common, especially during the winter when reduced exposure to sun light gives our bodies less opportunity to make the vitamin. Rates of vitamin D deficiency are higher among people with darker skin or groups with reduced sun exposure, such as nursing home residents.1,2,3 There is a correlation between these groups and those hit hardest by the pandemic.4,5 The difference in vitamin D levels could partly explain why Black and Asian citizens have been hit disproportionately hard by COVID-19, though socio-economic factors are likely to play an important role too.
So, what is vitamin D and what is the evidence that suggests it can help in the fight against coronavirus?
What is vitamin D and what are the benefits?
Vitamin D is not one chemical but many. The naturally occurring form that our bodies make in response to sunlight exposure is known as vitamin D3. In contrast, most supplements contain vitamin D2. Nonetheless, because the two forms have very similar functions, they are generally both referred to as vitamin D.
Vitamin D regulates the uptake of calcium and phosphorus in our bodies. Absorbing a sufficient amount of vitamin D is important for natural growth as well as the development of healthy bones and teeth. Crucially, vitamin D also facilitates normal immune system function; it has been found to decrease the risk of other viral respiratory infections, including influenza, especially in people with vitamin D deficiency.6
Does vitamin D protect against COVID-19?
There is mounting evidence to suggest that vitamin D can help to defend against SARS-CoV-2 infection, either by reducing the risk of severe outcomes or helping to prevent infection in the first place.
Prevention
Analysis of medical records by Professor David Meltzer at the University of Chicago found that those with deficient vitamin D had a 21.6 percent chance of testing positive for COVID-19, whereas the risk was reduced significantly to only 12.2 percent among those whose vitamin D levels were in the healthy range.7 This study used the medical records of 489 patients who had been tested for COVID-19 and had a vitamin D reading taken within the past year.
Another study by vitamin D expert Dr Michael Holick found that those with insufficient circulating vitamin D levels were 54 percent more likely to become infected with SARS-CoV-2.2 This was a large-scale study looking at data from more than 190,000 patients from all 50 US states.
Adverse events
Recently, there has been more evidence that vitamin D can also decrease the risk of the serious complications resulting from COVID-19.
Researchers from Boston University looked at blood samples from 235 patients admitted to hospital with COVID-19.8 Compared with those who were deficient, patients with sufficient levels of vitamin D were 51.5 percent less likely to die from the disease.
This study demonstrated that vitamin D sufficiency was linked to a significantly lower level of inflammatory markers and higher levels of immune cells, known as lymphocytes, in the blood. Higher levels of lymphocytes reduce the likelihood of cytokine storms, the immune reaction that causes many of the adverse effects and deaths from COVID-19.
Conclusion
It is hard to run a randomised controlled trial, the gold standard of medical evidence, on this subject as this would mean not treating some people with a deficiency that is associated with a wide array of negative effects. However, a stream of new evidence is appearing to suggest that vitamin D can help protect against COVID-19, and as winter draws closer, it is also worth remembering the general health benefits of vitamin D.
By Jess Quirke