An interesting case:
80 Year Old Vegan Not Supplementing with B12 Develops Nerve Problems Damage
Bernstein (2000, USA) describes a man in his eighties who had been in excellent health, and was a runner. He had been vegan for 38 years and attributed his ability to outperform younger people to his diet. In the span of a few weeks, mental disturbances began to set in. He cried, was confused, got lost, was incontinent, lost control of his bowels, and lost...