The effects of oral iron supplementation on cognition in older children and adults: a systematic review and meta-analysis

Systematic review and meta-analysis of randomized controlled trials of oral iron supplementation in people aged 6 years and older. The included studies were mainly in children and adolescents and pre-menopausal women; no trials included men or older adults.

Oral iron supplementation was evaluated across randomized trials using tablets, capsules, pills, or capsules delivering about 17 to 260 mg/day, or 2 to 4 mg/kg/day, for 4 to 29 weeks. The active regimens were compared mainly with placebo or no iron, and included elemental iron or ferrous iron preparations.

Oral iron showed some evidence of benefit for cognition, but the effects were domain- and subgroup-specific. Attention and concentration improved in older children and women, and IQ improved in anaemic children and women, whereas memory, psychomotor function, and scholastic achievement were not improved in other groups. Overall, the findings suggest a modest positive effect of iron on selected cognitive outcomes, but not a broad cognitive benefit.

The evidence base was limited by small sample sizes, short treatment durations, and generally weak study methods. The review also noted potential publication bias and limited generalizability because no studies included men or older adults, and follow-up rarely approached one year.