Latest research in:
The amount of Vit D given was 25-50 micrograms per day.
I'm amused they say "Going to see your GP is a key part of the message we want to give - I don't think it would be appropriate to just start taking vitamin D without knowing whether you have vitamin D deficiency or not and we don't yet know what the threshold of vitamin D is below which you will have a benefit."
That would help if GPs actually knew anything about Vit D apart from getting rickets if you're deficient! But an interesting read all the same.