It is known to us in functional medicine world that vitamin D supplementation is a basic and one of the core supplements that I feel is a universal need for our area of the world.  It has been estimated that vitamin D deficiency is extremely common especially the further away you live from the equator.  

I certainly have seen this in practice living here in the Northeast.  There is an interesting article that uses fatality rates (number of COVID deaths / the number of confirmed COVID cases) and notes mortality from the virus increased with latitude.  There are outliers of course but for the most part researchers at John Hopkins estimated fatality rate 6 % in the northern states compared to 3 % in the southern states!  Vitamin D production is stimulated by sun exposure to our skin and hard to get from food alone.  We know that vitamin D is an important modulator of the immune system.  Outbreaks for viral infections peak in winter months when our sun exposure and thus our vitamin D levels are at their lowest.  In addition, vitamin D deficiency promotes a more inflammatory state and in the case of COVID-19, we know that the inflammatory cytokine storm is a hallmark in people with more severe manifestations. 

 I feel it is of course best to obtain vitamin D levels periodically to know if we are getting the right amount.  It is usually a safe bet to take 2000 – 5000 IU daily and I have included it in my anti-viral maintenance regimen.  Because it is the kind of vitamin that will build up in your system, checking levels are important but it is very rare that I see a level that exceeds the safe range in blood.    I tend to just reduce dosing in the summer but this year, I am feeling more inclined to test to make sure we are keeping those levels optimized.