Vitamin B12

Research summary

• 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.
• However, the evidence for supplementation benefiting cognition in the broader population is weaker than commonly assumed: a Cochrane review found insufficient evidence that B12 improves cognition, and a separate Cochrane review of vitamin and mineral supplementation broadly found no clear benefit for maintaining cognitive function in cognitively healthy people.
• More recent meta-analyses of B-vitamin supplementation report modest, inconsistent effects on cognitive decline and dementia risk.
• A parallel story holds for cardiovascular disease: B12 (with folate and B6) reliably lowers blood homocysteine levels, but two independent Cochrane reviews of homocysteine-lowering interventions found this does not translate into a clear reduction in cardiovascular events.
• The clearest, best-supported use case remains treating diagnosed deficiency rather than general supplementation.