I have diet related b12 deficiency (I have a vegetarian/vegan diet and knew nothing about b12 until I became ill) and have had pretty serious problems caused by it and I am still having neurological problems which I have voiced regularly on this site.
I was reading the NHS site today and came across this section:
If your vitamin B12 deficiency is caused by a lack of the vitamin in your diet, you may be prescribed vitamin B12 tablets to take every day between meals. Alternatively, you may need to have an injection of hydroxocobalamin twice a year.
People who find it difficult to get enough vitamin B12 in their diets, such as those following a vegan diet, may need vitamin B12 tablets for life.
Although it's less common, people with vitamin B12 deficiency caused by a prolonged poor diet may be advised to stop taking the tablets once their vitamin B12 levels have returned to normal and their diet has improved.’
My doctor and the nurses equate b12 deficiency with PA and have completely dismissed my neurological damage which relates to brain malfunctions. I was wary of pushing my case given their stance and, reading this statement from the NHS, I think I was very wise to do so.