The change of the staple diet of black South Africans from sorghum to maize (corn) is the cause of the epidemic of squamous carcinoma of the oesophagus

Summary

The change of the staple diet of Black South Africans from sorghum to maize (corn) is the cause of the epidemic of squamous carcinoma of the oesophagus. For many years sorghum was the staple diet of Black South Africans. From approximately the early part of the twentieth century, maize gradually replaced sorghum. Squamous carcinoma of the oesophagus was infrequent in the first half of the twentieth century, rising slowly to current epidemic proportions. Fusarium fungi grow freely on maize, producing fumonisins, which reduce nitrates to nitrites and synthesise cancer-producing nitrosamines. Nitrosamines are the presumed carcinogens. Fusarium fungi do not grow well on sorghum, the production of fumonisin from sorghum being two orders of magnitude lower than maize. The higher incidence of oesophageal cancer in Black males is ascribed to their greater consumption of traditional beer, which is produced by fermenting maize. Patients with oesophageal cancer consume more beer than controls. Countries in Africa, in which the staple food is sorghum, have a low incidence of squamous carcinoma of the oesophagus.

Crops from various parts of the country should be examined for Fusarium fungi and nitrosamines. The nitrosamine content of traditional beer should be assessed. If nitrosamines are detected, their carcinogenic potential should be studied experimentally. Should these tests prove positive, it would be vital to break the Fusarium-nitrosamine-cancer chain.

Introduction

Until the 1950s carcinoma of the oesophagus was comparatively rare in the Black population. At the South African Institute for Medical Research in Johannesburg from 1912 to 1927, no cases of oesophageal cancer were diagnosed in Black patients, although over 200 primary hepatocellular carcinomas of the liver were encountered [1]. In the three year survey (1953–1955) of Higginson and Oettle [2] 53 cases were diagnosed. In 1960 the histopathology laboratory at Baragwanath Hospital yielded 87 cases. The 10-year survey (1966–1975) at the same hospital by Isaacson [1] yielded 1331 cases with a male: female ratio of 5:1. The current incidence at Baragwanath hospital is more than 1 case per day.

Dietary factors may be important in the predisposition to oesophageal cancer [3]. In 1975 Ivankovic et al. [4] suggested that nitrosomines might play a role. Several authors have suggested mouldy cereals containing the fungus Fusarium moniliforme, may contain carcinogenic substances, which may play a role in the causation of oesophageal cancer [5], [6]. The induction of oesophageal cancer experimentally by diethylnitrosamine has been known for many years [7]. A role for nitrosamines in humans has not yet been demonstrated. Neither has a definitive role for Fusarium been elucidated.

For many years the staple diet of the Black people of South Africa was sorghum. From approximately the turn of the 20th century, maize (corn) gradually replaced sorghum. The reason for this was probably economic in that the yield from corn is greater. It is suggested that the transformation from sorghum to corn as the staple food plays a significant role in the aetiology of squamous carcinoma of the oesophagus in Black South Africans.

This hypothesis links the roles of Fusarium, nitrosamines, sorghum and corn.