Iron vs Vitamin B12

for energy / fatigue

Stronger evidence: Iron

Stronger effect: Iron

Safety: No notable interactions recorded for either.

For energy / fatigue, Iron has the stronger evidence grade.

grade A high certainty

reliably reduces fatigue when iron deficiency / IDA is present; no benefit when iron-replete

18–65 mg/day, iron-deficient adults (esp. menstruating women)

grade C low certainty

corrects fatigue when B12 deficiency is present; no energy benefit in replete people

RDA-to-high oral, adults

sources: PMID:10000007 · PMID:10000010