That is a good question that I don't know that the jury is completely out on it yet.

One doctor I follow believes that all the associational data supporting the idea that vitamin D levels are so important for prevention of bad outcomes for viral infections thinks the low vitamin D levels are just a marker of other problems, namely metabolic syndrome. In other words it is associated with the problem but not the core cause. The reason he believes this is that studies where vitamin D was supplemented to bring levels up was not all that successful in disease prevention or better outcomes. That may or may not be correct, but it is one line of thought on the subject. In his way of thinking, fix the metabolic problems (insulin resistance and resulting over weight and poor metabolic health) that would be fixing the core problem.

From what research I have done it is extremely hard to overdose on vitamin D. It takes large doses for quite a while to do so to the point there can be toxicity. So my plan of attack has been to go ahead and take the 5,000 unit D pills with 100 mcg of vitamin K2 through the summer also. Just some time out in the sun with skin exposure can get tens of thousands of units so it appears to me the body is used to dealing with large doses of D. I definitely am taking the K2 with the D3 supplement though. K2 is very important and works along with the D3 to help determine where calcium goes in the body (you want it in the bones and hard tissues, not in the soft tissues like arteries). At least that is what I have heard. A person needs to do their own research and make up their own mind. Definitely don't listen to me. Because I do not know.

There is more than one avenue of thought on vitamin D3. I'm not sure anyone knows with absolute certainty.

It seems like any more I wear a long sleeve shirt much of the time and all the exposure I get to the sun in the summer is just my hands and neck, which are dark tanned. So not sure how much sun exposure I even get in the summer. My MIL is older and she hardly gets outside, let alone much sun, so we supply her with the pills year around.

That is my idea on the subject. I realize it is not a very good answer to the question.

Here are the two sources we have used for vitamin D3/K2 supplement. I am not promoting them. I get no commission.  They have not killed me yet so they seem to be ok.

https://www.amazon.com/gp/product/B08X4V8QMQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B06Y3X5SDZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1