I've already explained this. Go back and read it again.Again, based on common sense, how could those 1% studies be accurate when I can double the US infection count (which there's no way it's not at least double) and get an IFR of under 1% in a wealthy country with a higher than average elderly population?
There is no convincing evidence that loading up with Vit D above existing guidelines improves immune system function.Technically insufficient as defined by the paper, which is a UK study. Vitamin d is no longer just viewed as important for bone health and avoiding rickets, which is what the UK's recommendations are based off. We need more vitamin d than we've thought. The fact that the UK recommendation is a 400 IU supplement daily shows how behind the times they are. What you need to not get rickets and what your immune system needs are 2 different values.
Now, that out of the way... the UK recommendations are in line with virtually every major Western health body. The NIH, for instance, recommends 15 micrograms a day: that's total. Bearing in mind a chunk comes through diet, there is absolutely no need at all for more than 10 micrograms supplement (with the exception of people with certain conditions). .
I couldn't give a monkey's what that paper decides to define as "insufficiency". If you really understand what happens when these levels are estimated, you'd realise they are very vague, and usually conservative, measures. What actually defines the 50 nmol/L is that a long time ago they had a conference and thought that was a pretty good sort of ballpark concentration for a person to have. It was in no way an argument that 40 nmol/L, or 30, or even 20 was not adequate for a normal human being, never mind considering individual variation. That's why actual "deficiency" is the much lower figure that needs to be watched out for where there is substantial evidence there may be problems.
Also you need to bear in mind that Vit D is actually relatively toxic for a nutrient. If you consider how scarce Vit D is in normal diet, then obviously we are not designed to consume large quantities of it. Although full on toxicity is rare, even at non-toxic but high levels it can cause increased calcium metabolism with risk of illness, kidney stones, and is associated with greater mortality. So when they are recommending about 10-25 microgram supplementation a day, they do so because it will almost certainly ensure good levels of Vit D with minimal risk of adverse effects from overconsumption.
The current Vit D shit is almost certainly another one of those transient fads that run through the nutrition world occasionally because someone read a paper and grotesquely overhyped it, just like years ago people thought it was a great idea to stuff themselves full of huge quantities Vit C to no significant benefit whatsoever. And they all said things like "Linus Pauling does it and he's got a Nobel Prize" too, but it was still overhyped bullshit.