Iron and Calcium Supplementation for Reducing Blood Lead Levels: A Systematic Review and Meta-Analysis

Approximately half of children in low- and middle-income countries have elevated blood lead levels. The WHO recommends calcium and iron supplementation for lead-exposed individuals with nutritional deficiencies, but acknowledges this is based on “very low-certainty evidence.” We conducted a systematic review and meta-analysis of 11 randomized controlled trials (n=3,666 enrolled). Across all seven calcium studies, the pooled effect on blood lead was −1.33 μg/dL (95% CI: −2.87 to +0.21 ; p=.078 ), attenuating to −0.36 μg/dL when restricted to 4 low-risk-of-bias studies. Iron supplementation reduced blood lead by −0.31 μg/dL (95% CI: −0.61 to −0.02 ; p=.045 ). The three studies from settings with widespread calcium deficiency—which are also the three high-risk-of-bias studies—showed substantially larger effects. We rate certainty of evidence as very low for calcium and moderate for iron. These interventions offer modest potential benefits at low cost but cannot substitute for primary prevention.