title: 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.
authors.affiliation: Department of Epidemiology, University of Washington, Seattle, WA, United States of America.
authors.forename: Torin
authors.initials: T
authors.lastname: Schaafsma
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, WA, United States of America.
authors.forename: Jon
authors.initials: J
authors.lastname: Wakefield
authors.affiliation: Section of Environment and Radiation, International Agency for Research on Cancer, Lyon, France.
authors.forename: Rachel
authors.initials: R
authors.lastname: Hanisch
authors.affiliation: Section of Cancer Surveillance, International Agency for Research on Cancer, Lyon, France.
authors.forename: Freddie
authors.initials: F
authors.lastname: Bray
authors.affiliation: Section of Environment and Radiation, International Agency for Research on Cancer, Lyon, France.
authors.forename: Joachim
authors.initials: J
authors.lastname: Schüz
authors.affiliation: Centre for Environmental Geochemistry, Inorganic Geochemistry, British Geological Survey, Nottingham, United Kingdom; School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, United Kingdom.
authors.forename: Edward J M
authors.initials: EJ
authors.lastname: Joy
authors.affiliation: Centre for Environmental Geochemistry, Inorganic Geochemistry, British Geological Survey, Nottingham, United Kingdom.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Watts
authors.affiliation: Section of Environment and Radiation, International Agency for Research on Cancer, Lyon, France.
authors.forename: Valerie
authors.initials: V
authors.lastname: McCormack
mesh_terms: D000328:Adult; D000349:Africa / Q000453:epidemiology; D002294:Carcinoma, Squamous Cell / Q000453:epidemiology* / Q000209:etiology; D004938:Esophageal Neoplasms / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D018977:Micronutrients / Q000172:deficiency*; D008875:Middle Aged; D009752:Nutritional Status; D012643:Selenium / Q000172:deficiency*; D017678:Sex Distribution; D015032:Zinc / Q000172:deficiency*
chemical_list: D018977:Micronutrients; D012643:Selenium; D015032:Zinc