Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults: A meta-analysis and systematic review

Eighteen studies (12 randomised trials, 6 pre-post) covering 1,408 people — 1,176 menstruating adults averaging 34.6 years and 204 children and adolescents averaging 13.9 years — were reviewed, with 16 meta-analysed. In the randomised trials, iron supplementation improved anxiety (d = 0.34), fatigue (d = 0.34), physical well-being (d = 0.42), cognitive intelligence (d = 0.46) and short-term memory (d = 0.53), but not attention or depression. Uncontrolled pre-post studies reported much larger apparent effects for depression (d = 0.93), fatigue (d = 1.01) and overall psychiatric symptoms (d = 1.13). Crucially, effects disappeared when iron-deficient participants were excluded, indicating benefit is confined to those who are actually iron deficient even without anaemia.