I cannot answer your question, but following my latest consultation, my neuro has recently confirmed in writing I should be on 2000 IU per day (which is fine, as I have been ever since before diagnosis, when the penny began to drop it was MS).
He also recommends all first degree relatives should be doing the same (I can already predict my brother’s reaction to that: “Pah, cobblers! I don’t need to worry about MS - it’ll never happen!”)
Ironically, though, I have never, ever been prescribed them. I find it really odd that the NHS - through my consultant - should be recommending I I take something, but never offering to supply it.
True, Vitamin D is among the less expensive things one might be advised to take, and a prescription is almost certainly dearer than the over-the-counter cost. Then again, although I still pay for my prescriptions (despite having v. low income AND not eligible for any benefits, due neither sick nor poor enough yet), I always invest in a prepay certificate, which means I do not pay any extra for my medicines, no many how many I have, so simply adding Vitamin D to the list would effectively be free (to me) instead of self-funded.
Can’t think of any other case where a doctor says you should be on something, but you are supposed to go out and buy it yourself.
I am not sure the Society make blanket medical recommendations: I think they would say: “Ask your neuro.” Sorry this doesn’t help much - especially if your neuro says something completely different to mine!