Research synthesisModerate evidenceMixed effect size4 studies · 4 beneficial · 0 neutral · 0 harmful
Across 4 studies, all reported beneficial effects of iron supplementation or fortification on reducing iron deficiency, with effect sizes ranging from small to large (2 large, 1 moderate, 1 small). The strongest evidence comes from meta-analyses in pregnant women and general populations, showing large reductions in iron deficiency risk (e.g., RR 0.24 for maternal deficiency at term; RR 0.36 for iron deficiency with food fortification). Doses varied widely (0.2–112.8 mg/day or per serving), and the most-studied population was pregnant women.
- Studied populations: pregnant women, general populations (including children over 2 years and adults)
Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). All 4 studies show significant beneficial effects, but the evidence quality for most is low-certainty due to risk of bias or imprecision. Doses and forms varied widely across studies (fortification vs. supplementation, different compounds), limiting direct comparability. The effect sizes were mixed (small to large), and no single dose or form emerged as clearly optimal.
Generated Jun 16, 2026