Is Vitamin B12 good for longevity?

The evidence points that way, though it's not yet conclusive. B12 deficiency is common enough in older adults to warrant real clinical attention, and a systematic review documents meaningful rates of subnormal B12 and associated anaemia in this group. That's reflected in an evidence score of 40/100 for its role in overall longevity, drawn from 10 studies, with an estimated impact on longevity rated limited (20/100).