Sphingoid base levels in humans consuming fumonisin-contaminated maize in rural areas of the former Transkei, South Africa: a cross-sectional study

Abstract

High incidences of oesophageal cancer are associated with the consumption of subsistence-grown maize by rural populations in the former Transkei region of Eastern Cape Province, South Africa. This cross-sectional study was conducted in the north-eastern magisterial area of Bizana (a previously low oesophageal cancer incidence area) and the south-eastern area of Centane (a previously high incidence area). Plasma and urine samples of male and female participants were analysed for the sphingoid bases, sphinganine and sphingosine. Good home-grown and visibly mouldy maize samples, collected from the households of the participants, were analysed for fumonisin B1, B2 and B3. Plasma sphinganine/sphingosine ratios in males and females were significantly lower (p < 0.05) due to lower sphinganine levels in Bizana compared to Centane. In contrast, the urinary female and combined (males + females) sphinganine/sphingosine ratios were significantly higher (p < 0.05) in Bizana due to the significantly lower (p < 0.05) urinary sphingosine levels. Interestingly, urinary sphingoid base levels were significantly lower (p < 0.05) in males than females within each area. Based on the mean total fumonisin levels in good maize, the estimated mean probable daily intake (PDI) was 5.8 µg kg−1 body weight day−1 in Bizana during 2000 and 4.4 and 6.7 5.8 µg kg−1 body weight day−1 in Centane during 1997 and 2000, respectively, exceeding the maximum tolerable daily intake proposed by JECFA. However, there was no significant difference in the mean total fumonisin levels in the maize between the magisterial areas. The observed differences in plasma and urinary sphingoid base levels could not be ascribed as a biomarker of fumonisin exposure and further studies at an individual level are required.