Last study I read put a 99% correlation on vitamin d deficiency and getting a severe case of covid19. Which was significantly more than age correlated on the same dataset.
Vitamin-D deficiency may cause severe covid-19, or severe covid-19 may cause vitamin-D deficiency (covid-19 affects the kidneys second worst after lungs it seems, and you need kidneys for vitamin-D processing), or a little bit of both.
Vitamin D is fat soluble and “buffered” in the body; all of which is to say that no one goes from good vitamin D levels to being vitamin D deficient in the time it takes to get infected and develop serious Covid-19 symptoms.
What is usually measured is the calcifediol - aka 25(OH)D - in the blood. It is the liver that produces calcifediol from cholecalciferol - aka vitamin-D3. The kidneys (mostly) then turn that in calcitriol, the actual hormon.
Vitamin-D2 aka ergocalciferol works similar in that is is eventually converted by liver and kidneys into calcitriol.
Ergocalciferol, calcifediol and it's various precursors can indeed be stored in fat tissue.
It is unclear however how severe covid-19 can affect the kidney and liver functions relating to this and release of substances from fat tissue.
Right now a lot of research seems to point in the direction that vitamin-D deficiency can indeed lead to more severe covid-19. At the same time there is different research suggesting that covid-19 itself messes with vitamin-D levels as well.
As someone who is severely Vitamin D deficient (I take 50,000IU a week via prescription and still have very low blood test results), both my GI doctor and PCP have indicated it as a risk factor if I was to get infected.
That seems very right. It doesn't matter if covid-19 causes/worsens deficiency or deficiency causes severe covid-19, or both. If you're already deficient the outcome will be that it gets even worse for a deficient person.
I was more making my initial comment thinking in the opposite direction: that people who are not deficient shouldn't feel overly secure (and take more risks) just because there is a correlation - with unclear causation.
You have to be careful in general whenever you are correlating two common features. If 80% of your deaths to a disease are among people who are overweight or obese, and 70% of your population is overweight or obese ... yes, there is a correlation. But it's a much weaker and less interesting correlation than if 20% of your population were overweight or obese, or if 97% of the people who died were obese or overweight.
So you made me curious and I googled. Not quite most everyone, it rather seems to be regional: under 20% in Northern Europe, 30-60% in rest of Europe, up to 80% in Middle East.
Huh, weird. I would have assumed deficiency would be inversely proportional to amount of sunshine. Do people in northern europe really experience so much more “sun on skin” time or is it wholly diet driven?
Melanin reduces the amount of vitamin D synthesized in the skin for the same reason it has protective effects against sunburns.
Historically this wasn't a problem since people with more melanin live in sunnier, more UV intense regions. In fact, pale skin may have been an adaptation as people moved north from the equator to combat the decrease in sun exposure/intensity. But people spend much less time outdoors today with AC and the internet, so vitamin D deficiency is especially prominent in dark skinned populations.
> The generally adequate vitamin D status in the Nordic countries is due to the use of cod liver oil and supplements (46) and vitamin D fortification, leading to a great improvement in Finland during the last decade (47).
Doesn't surprise me; here in the South we don't get deficient enough to cause obvious issues, so we don't pay attention to it.
At least in Sweden all children are given supplements, up to at least the age of 5, and just anecdotal, many of friends and grownups in my extended family do so too.
