Onyena et al. 2024 — Lactational Metal Exposure in Sub-Saharan Africa vs Mediterranean Europe
This systematic review and meta-analysis pooled data from 42 studies to compare breast milk concentrations of Cd, Pb, Hg, Se, and Fe between Sub-Saharan Africa and Mediterranean Europe, documenting dramatically higher toxic metal levels in SSA breast milk.
Key numbers
Weighted mean breast milk concentrations (µg/L) by region:
| Metal | Sub-Saharan Africa | Mediterranean Europe | p |
|---|---|---|---|
| Cd | 12.38 ± 1.21 | 0.22 ± 0.51 | <0.0001 |
| Pb | 14.96 ± 8.10 | 1.16 ± 4.00 | <0.0001 |
| tHg | 2.01 ± 1.37 | 0.95 ± 4.32 | 0.008 |
| Se | 7.38 | 13.09 | — |
SSA vs Mediterranean Europe: Cd 56×, Pb 13×, Hg 2× higher in SSA. Conversely, essential elements (Cu, Fe, Se) were significantly higher in Mediterranean Europe, suggesting nutritional differences as well as industrial contamination differences.
Methods
Systematic review + meta-analysis, 42 studies (25 SSA, 17 Mediterranean Europe). Statistical comparison of weighted means. Publication bias not quantified in available excerpt. Study investigated intrinsic factors (lactation stage, parity) and extrinsic factors (diet, smoking, dental amalgam, mining proximity).
Significant limitation: SSA studies disproportionately come from mining or industrial areas (Nigeria, Ghana, South Africa near mines); Mediterranean Europe studies largely from lower-exposure urban populations. Direct comparison may reflect publication bias toward high-exposure communities in SSA rather than representative regional averages.
Implications
Health: The Cd disparity (56×) is striking and reflects both dietary and environmental exposure differences. SSA Pb levels (mean ~15 µg/L) are above values in many high-income countries; driven by leaded gasoline legacy, artisanal gold mining, and e-waste processing.
Certification: Breast milk metal burdens in SSA indicate that lactational exposure to Cd and Pb may be a significant pathway for infant toxicant exposure in these regions, independent of dietary formula or food sources.