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Current status of research and gaps in knowledge of geophagic practices in Africa

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Overview

Theophilus C. Davies of Mangosuthu University of Technology provides an updated critical review of human geophagy in Africa. The paper identifies key knowledge gaps, compiles a bibliography of post-2005 literature, and outlines research priorities. It covers the nature of consumed Earth material, aetiology (micronutrient supplementation, detoxification, and other theories), animal geophagy, social and cultural dimensions, and the demerits of the practice including heavy metal ingestion and microbiological infection. The review notes that geophagy in Africa is most commonly recorded in pregnant women and children and that the practice is largely misunderstood by health practitioners and researchers alike.

Key numbers

Prevalence:

  • MUV (Medical University of Vienna, cited as ref 15) estimates 30-80% of Africans, especially women, eat clayey soil on a regular basis consuming 100-400 g per day (source p. 3)
  • Geophagy in pregnancy (GiP): a 2016 meta-analysis (Fawcett et al., cited as ref 18) found worldwide prevalence of pica during pregnancy varied substantially; Africa was among the highest-prevalence regions

Composition and contamination context:

  • African soils are diverse; more than 60% of World Reference Base soil types are represented on the African continent, with hot, arid or immature soil assemblages predominating (>60% of land area covered by sandy soils 22%, shallow stony soils 17%, and young weakly developed soils 11%) (source p. 3)
  • Geophagic material can contain potentially harmful elements (PHEs) at total concentrations significantly higher than WHO guideline limits (source p. 8, citing refs 87, 88)

Bioavailability:

  • The bioavailability of a PHE is the fraction reaching the human systemic circulation from the gastrointestinal (GI) tract; it is strongly dependent on bioaccessible soil-PHE (source p. 8)
  • Both bioavailability and bioaccessibility are influenced by soil mineralogy, particle size, morphology, age, gender, socioeconomic status, and WHO nutritional status (source p. 8, citing refs 90, 91)
  • In vitro bioavailability and bioaccessibility (IVBA) procedures developed by research groups including USEPA (United States Environmental Protection Agency) are described; methodological criticisms exist including lack of CRMs and insufficient in vivo validation data (source p. 8, citing refs 92-94)

Iron and anemia context:

  • Excess Earth material consumption can interfere with bioavailability of minerals and vitamins, potentially leading to micronutrient deficiencies (source p. 8, citing refs 65, 78, 79)
  • Some researchers (66, 79, 80) believe excessive consumption of Earth materials can interfere with bioavailability of micronutrients, potentially exacerbating iron and vitamin deficiency and causing infectious disease, lead poisoning, intestinal impaction, and hyperkalemia (source p. 9)

Research gaps explicitly stated:

  1. Accurate determination of bioavailability and bioaccessibility of PHEs in consumed Earth material from a particular contaminative source (source p. 9)
  2. During pregnancy, excessive amounts of soil consumed and potential implications on health, including for cobalamin (vitamin B12) supplementation; national guidelines on micronutrient deficiency control are largely silent on the subject of GiP (source p. 9)
  3. Enhancement of unitary or non-unified approach in design of in vitro studies in bioavailability and bioaccessibility of geophagy (source pp. 10-11)
  4. Role of geophagy in supplementing cobalamin and possibly inducing pica in pregnancy (source p. 6)
  5. Accurate determination of types of clay consumed and their mineralogy and geochemistry (source p. 10)

Social and cultural context:

  • Table 2 of source lists published perspectives on geophagy in Africa by region: psychiatric disease (urban South Africa), religious geophagy (Christianity, Islam, Hinduism, hoodoo folk magic worldwide), cultural norm (Africa, India, worldwide), geophagy as social and cultural factors (Geita District, Tanzania), and other perspectives

Microbiological risks:

  • Soil-transmitted helminth infections affect approximately 1.5 billion people worldwide; eggs present in soil areas with poor sanitation can contaminate geophagic material (source p. 8)
  • Studies cited (101, 103, 104) show occurrence of geohelminth infection among children in Africa is linked with eating dirt; specific species involved remain unclear in most cases
  • Dental damage (enamel erosion), colon obstruction, peritonitis, eclampsia, and iron deficiency anemia are among the clinical demerits cited (source p. 9, citing refs 108, 118)

Evidence Fitness

This is a critical review (EF-4: context only). No primary measurements are reported; all quantitative values are syntheses of cited studies. The prevalence estimates (30-80% of Africans consuming clay; 100-400 g/day) are drawn from a single cited source (MUV, ref 15) and are themselves averages across heterogeneous populations. The bioavailability discussion is conceptual rather than empirical. The paper does not provide clay-specific metal concentration values in tabular form; it describes PHE contamination as a known hazard with reference to other studies that contain the actual measurements. This review is valuable as a framework document and research-gap identification resource, but its numerical claims require tracing to the primary cited studies before use as occurrence data.

Methods (brief)

Updated critical review. Literature search focused on post-2005 publications on geophagy in Africa and other animal geophagy. The author compiled a bibliography intended to serve as a baseline and rough search framework for researchers in Medical Geology and allied fields. No systematic search protocol, PRISMA statement, or risk-of-bias assessment is described. The author is a sole author affiliated with a South African university.

Implications

Certification: Establishes that the bioavailability of PHEs in consumed Earth material depends critically on soil type, mineralogy, and consumer physiology, and that total-metal concentrations overestimate bioavailable exposure. This is relevant to interpreting clay concentration data: total-metal values from AAS or ICP-MS are upper bounds on what can be absorbed, not equivalent to what is actually absorbed.

Courses: The table of aetiology theories (Table 1 of source) is well-structured for teaching. The micronutrient supplementation theory (iron, calcium, cobalamin) and detoxification theory (binding mycotoxins, bacterial endotoxins, plant secondary compounds) provide mechanistic context for why populations practice geophagy despite awareness of health risks.

App: No primary concentration data applicable to the contamination profile.

Microbiome: The review (Figure 6 of source) illustrates how soil microbiota in pre-industrial cycles can directly influence human intestinal microbiome through contact. This soil-to-gut microbial pathway is distinct from, and additional to, the metal exposure pathway. It is relevant to the metal-gut relationship.

Provenance notes

Open access, CC BY license. Full text retrieved from PubMed Central (PMC9987423). SHA-256 verified against MANIFEST.csv for HMI-FILL-0002. No retraction flag. DOI resolves. Single author; no conflicts of interest declared.

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