Vitamin B12 vs Iron
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.
Vitamin B12
grade C low certainty
corrects fatigue when B12 deficiency is present; no energy benefit in replete people
RDA-to-high oral, adults
Iron
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)
sources: PMID:10000010 · PMID:10000007