Quote Originally Posted by Mike T View Post
Is a good Vitamin D level just a lifestyle marker - of a good diet (oily fish, mushrooms) and sunshine exposure from outdoors exercise, in other words are we looking at association rather than causation.
Vitamin D does increase calcium absorption, and there are concerns re kidney stones and vascular calcification if excessive supplements are taken. Don't take more than 10 micrograms/400 international units except under medical supervision.
I have heard that argument, suggesting it might be association rather than causation. That possibility can't be discounted. There was a recent Spanish study however where one group of Covid patients were given doses of vitamin D, while the other group weren't. The outcomes for the first group were significantly better than for the latter.

I'm surprised that there isn't more of an official drive from the Government to combat vitamin D deficiency. What's the worst that could happen? It may be that in terms of Covid it is just association rather than causation as you suggest and vitamin D has no effect. There would still be other health benefits for bones, teeth and the immune system. Not to mention the links with improved mental health - pretty important right now. The best case could be that vitamin D is a game changer with regard to Covid and thousands of lives are saved. There is literally no downside to people taking vitamin D supplements in autumn/winter. They are safe and also happen to be cheap as chips.

I was interested in the figure you gave for dosage. That seems to be very low for winter in a northern location like the UK. I looked at my supplements and they are 25 mcg / 1000 IU as I thought - one to be taken per day. This article addresses how much you should take.

https://www.healthline.com/nutrition...amin-d-to-take

It says:

All things considered, a daily vitamin D intake of 1000–4000 IU, or 25–100 micrograms, should be enough to ensure optimal blood levels in most people.

4000 IU is the safe upper limit according to the Institute of Medicine (IOM). Make sure not to take more than that without consulting with a health professional.

The issue of overdose and toxicity is addressed.

The upper level of harmless intake is set at 4000 IU, or 100 micrograms, per day.

However, up to 10,000 IU per day has not been shown to cause harm to healthy individuals

That being said, very few people actually need more than 4000 IU a day.

A study of 17 thousand people taking varying doses of vitamin D, up to 20,000 IU/day, did not demonstrate any signs of toxicity. Their blood levels were still lower than the upper range of normal, which is 100 ng/ml, or 250 nmol/l.