Abstract
Geophagia, the intentional practice of consuming soil, occurs across the African esophageal cancer corridor, particularly during pregnancy. We investigated whether this practice is linked to endemic esophageal squamous cell carcinoma (ESCC) in this region. We conducted ESCC case‐control studies in Tanzania, Malawi and Kenya. Cases were patients with incident histologically/clinically confirmed ESCC and controls were hospital patients/visitors without digestive diseases. Participants were asked if they had ever eaten soil (never/regularly/pregnancy‐only). Odds ratios (OR) are adjusted for sex, age, tobacco, alcohol, country, religion and marital status. Overall, 934 cases (Malawi 535, Tanzania 304 and Kenya females 95) and 995 controls provided geophagia information. Among controls, ever‐geophagia was common in women (Malawi 49%, Kenya 43% and Tanzania 29%) but not in men (10% Malawi, <1% Tanzania). In women, ESCC ORs were 1.25 (95% CI: 0.70, 2.22) for regular versus never geophagia and 0.88 (95% CI: 0.64, 1.22) for pregnancy‐only versus never. Findings were stronger based on comparisons of cases with hospital visitor controls and were null using hospital patients as controls. In conclusion, geophagia is too rare to contribute to the male ESCC burden in Africa. In women, the practice is common but we did not find consistent evidence of a link to ESCC. The study cannot rule out selection bias masking modest effects. Physical effects of geophagia do not appear to have a large impact on overall ESCC risk. Research with improved constituent‐based geophagia exposure assessment is needed.
Highlights
Analogous to the Asian esophageal cancer belt, an African esophageal cancer corridor stretches from Ethiopia down to the Eastern Cape of Southern Africa.[1]
To understand the population prevalence and patterns of geophagia practice and identify factors that might lead to confounding of any geophagia-esophageal squamous cell carcinoma (ESCC) association, we examined how geophagia habits in controls varied by socio-economic factors and ESCC risk factors, tested using chi-squared statistics
Sensitivity analyses were conducted by type of control to investigate the impact of the choice of the control group, and we examined the potential effect modification by age (
Summary
Analogous to the Asian esophageal cancer belt, an African esophageal cancer corridor stretches from Ethiopia down to the Eastern Cape of Southern Africa.[1]. In 2009, Ogbonnaya reported a prevalence of 63% in Kenya,[16] while in Tanzania Kawai reported a prevalence of 29%.17 In these countries the practice is known as kula udongo in kiSwahili, while in Malawi the practice of geophagia, kudya dothi in chichewa, is considered culturally as a confirmatory sign of pregnancy.[18] In contrast to women, there are limited studies on geophagia involving men, presumably because the prevalence is low.
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