Africa's Oesophageal Cancer Corridor: Geographic Variations in Incidence Correlate with Certain Micronutrient Deficiencies

Abstract

Background: The aetiology of Africa's easterly-lying corridor of squamous cell oesophageal cancer is poorly understood. Micronutrient deficiencies have been implicated in this cancer in other areas of the world, but their role in Africa is unclear. Without prospective cohorts, timely insights can instead be gained through ecological studies.

Methods: Across Africa we assessed associations between a country's oesophageal cancer incidence rate and food balance sheet-derived estimates of mean national dietary supplies of 7 nutrients: calcium (Ca), copper (Cu), iron (Fe), iodine (I), magnesium (Mg), selenium (Se) and zinc (Zn). We included 32 countries which had estimates of dietary nutrient supplies and of better-quality GLOBCAN 2012 cancer incidence rates. Bayesian hierarchical Poisson lognormal models were used to estimate incidence rate ratios for oesophageal cancer associated with each nutrient, adjusted for age, gender, energy intake, phytate, smoking and alcohol consumption, as well as their 95% posterior credible intervals (CI). Adult dietary deficiencies were quantified using an estimated average requirements (EAR) cut-point approach.

Results: Adjusted incidence rate ratios for oesophageal cancer associated with a doubling of mean nutrient supply were: for Fe 0.49 (95% CI: 0.29-0.82); Mg 0.58 (0.31-1.08); Se 0.40 (0.18-0.90); and Zn 0.29 (0.11-0.74). There were no associations with Ca, Cu and I. Mean national nutrient supplies exceeded adult EARs for Mg and Fe in most countries. For Se, mean supplies were less than EARs (both sexes) in 7 of the 10 highest oesophageal cancer ranking countries, compared to 23% of remaining countries. For Zn, mean supplies were less than the male EARs in 8 of these 10 highest ranking countries compared to in 36% of other countries.

Conclusions: Ecological associations are consistent with the potential role of Se and/or Zn deficiencies in squamous cell oesophageal cancer in Africa. Individual-level analytical studies are needed to elucidate their causal role in this setting.

Fig 1. Eastern and western rift valley overlaid on a map of oesophageal cancer incidence rates in Africa, GLOBOCAN 2012.

Countries are only named on the graph for women, to simplify the display.

Fig 2. Scatterplots of country-specific oesophageal cancer incidence rates vs mean micronutrient intake per capita.

A country’s EC incidence rates are for both sexes combined and are age-standardized to the world standard population. Both axes are plotted on logarithmic scales. Vertical dashed lines indicate estimated average requirements (EAR) in adults: male EARs (blue), female EARs (pink) and non sex-specific EARs (black). For Cu and Mg, and, in men, Fe, EARs lines are suppressed as they are below the mean levels in every country. Circle sizes are proportional to the square root of the total number of EC cases for each country.

Fig 3. Mean national supplies of Fe, Mg, Se and Zn, overall and by source, Africa, followed by the country’s oesophageal cancer incidence rate.

Countries are ranked by esophageal cancer incidence rate (age-standardized, world population, both sexes). Vertical lines indicate the EAR (blue for men, red for women, and black if both sexes are combined.