Overview
Vulla and colleagues from the University of Malawi and the University of Dar es Salaam conducted a narrative review of the evidence on geophagy during pregnancy in sub-Saharan Africa. The review synthesized published literature on prevalence, cultural and physiological drivers, nutritional consequences, toxic metal exposures, associations with maternal anaemia, and intervention strategies. The authors report that geophagy is practiced by an estimated 36% of pregnant women globally, with some sub-Saharan African settings recording prevalence as high as 73%. The principal heavy metal concern is the documented presence of lead, arsenic, cadmium, mercury, and chromium in geophagic materials from Ghana, Tanzania, Nigeria, South Africa, Cameroon, and elsewhere, with several reported concentrations exceeding WHO or FAO reference values and generating carcinogenic or non-carcinogenic hazard quotients above acceptable thresholds.
Key numbers
No primary measurements are reported. The review summarizes findings from earlier studies:
Table 1 (p. 8): Heavy metals identified in geophagic materials
| Metal | Common presence | Major health risk |
|---|---|---|
| Lead | Very common | Neurotoxicity, anaemia, cancer risk |
| Arsenic | Natural geological deposits | Carcinogen (skin, lung, bladder) |
| Cadmium | Agricultural and environmental contamination | Kidney damage and cancer |
| Mercury | Industrial contamination | Neurotoxicity, developmental toxicity |
| Chromium | Industrial areas | Strong carcinogen |
Table 2 (p. 9): Selected studies from sub-Saharan Africa on heavy metal contamination
- Nkansah et al. (Ghana, Kumasi, white clay): arsenic and lead exceeded WHO/FAO maximum permitted daily intake; noted carcinogenic risk from arsenic and lead.
- Mouri et al. (South Africa, Limpopo, 12 geophagic materials): arsenic, chromium, and lead exceeded recommended levels; risk assessment based on geochemistry and XRF.
- Kortei et al. (Ghana, Volta Region): target hazard quotients (THQ) for arsenic, lead, and nickel exceeded 1; total target hazard quotient (TTHQ) exceeded 15, indicating high level of unsafety.
- Ekosse et al. (Cameroon, geophagic clay): non-carcinogenic risk indices for iron, cobalt, nickel, chromium, copper, zinc, lead were below 1 in that study; carcinogenic risk for nickel and chromium above 10^-4.
- Rukondo et al. (Tanzania, dry soil sticks): cancer risk index (CRI) minimal but present; carcinogenic risk for nickel and chromium above 10^-4 in some sites.
Prevalence (Figures 2-3): Ghana approximately 50%, Kenya approximately 65%, Tanzania approximately 50%, Nigeria approximately 50%, South Africa approximately 50%, Uganda approximately 50%, Malawi approximately 30%, Zambia approximately 30%, Namibia approximately 45%, Sudan approximately 35%, Congo DRC approximately 50%.
Common types of geophagic materials (Section 3.3): clay-rich soils including bentonite and kaolin, fertile earths, mud from specific sites, and mineral-rich soils.
Methods (brief)
Narrative review. Literature retrieved from PubMed, Scopus, Web of Science, ScienceDirect, and Google Scholar using Boolean search strategies. Reporting guided by the Scale for the Assessment of Narrative Review Articles (SANRA). No formal meta-analysis or statistical pooling was conducted. Inclusion criteria: peer-reviewed articles, review papers, books, conference proceedings, and reports from recognized organizations reporting geophagy or pica during pregnancy. Exclusion criteria: non-maternal population focus, insufficient information.
LOD/LOQ: not applicable (review). CRM and recovery: not applicable.
Evidence Fitness
EF-4 (review synthesis). No new primary measurements. The review is a useful map of the literature on geophagic material contamination across sub-Saharan Africa but does not report or verify the numerical values it cites from primary sources. The Table 2 summary of carcinogenic and non-carcinogenic risk quotients draws on multiple primary studies at different locations and with different matrices. This paper is evidence for the existence and direction of the problem, not a source of specimen-level concentration data. Use primary studies (Kortei 2019, Kortei 2020, Rukondo 2024) for concentration data.
Implications
Products: Provides regulatory and risk context for the supplements-clay-mineral-earth row. The consistent cross-regional finding that geophagic clays carry lead, arsenic, cadmium, mercury, and chromium at concentrations that generate hazard quotients above 1 supports classifying this row as a heavy-metal-elevated category requiring testing. The prevalence data documents the scale of direct clay ingestion in vulnerable populations.
Courses: Useful for the dietary exposure module. The prevalence data, geographic map, and common material types (bentonite, kaolin) are strong anchors for describing geophagy as a recognized oral exposure pathway.
Related evidence
- Clay and geophagy
- Elemental minerals and microbial compositions as well as knowledge and perceptions regarding kaolin (clay) consumption by pregnant women in the Ho municipality of Ghana
- Potential health risk assessment of toxic metals contamination in clay eaten as pica (geophagia) among pregnant women of Ho in the Volta Region of Ghana
- Mineral composition and heavy metal risk assesment of selected geophagic soils from Tanzania
- Geophagia among pregnant women: evaluating the microbiological and toxicological safety of calabash chalk and its implications on maternal health
Update history
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