I've just read an article on the importance of B vitamins and cognitive decline:
Which led me to an article in the Mail Online:
The flag up for me and it's relevance to this forum was the following, taken from the above:
"The diabetes drug metformin also reduces B12 absorption by 30 per cent, according to a trial published in the BMJ this summer".
Now, for me as an omnivore, a reduction in B12 opf 30% would alarm me greatly, but for a vegetarian or vegan would be an unmitigated disaster, as the only reliable source (I emphasise reliable) is from animal foods.
The take home? If you are on Metformin then supplementation of B12 could be advisable and if vegan essential.
As usual, do your own research and make your own mind up - this should not be considered medical advice.