Effects of zinc fortification on the plasma fatty acid composition of Beninese school children : a randomised, double-blind controlled trial

Abstract

Introduction The lack of a specific and sensitive zinc (Zn) status biomarker is problematic. The linoleic acid: dihomo-γ-linolenic acid (LA:DGLA) ratio has been suggested by some researchers to be a Zn status marker. This is because Zn and fatty acids (FA) are known to interact, as Zn and FA deficient individuals present similar symptoms and physical manifestations. Although the mechanism by which Zn and FA interact is not fully understood, it is suggested that they interact through the FA synthesis pathway. Zn deficiency is suggested to impair the activity of desaturase enzymes, (desaturase enzymes are responsible for the conversion of essential fatty acids into longer-chain polyunsaturated FA) thereby causing a decrease in tissue long chain polyunsaturated metabolites. Zn supplementation in Zn deficient rats is known to affect their FA status, but little is known about effects of Zn fortification on the FA status in humans. There is also limited data on the FA status of African children as well as data on Zn and FA interactions in humans. Therefore the main aim of this study was to investigate whether there were associations between baseline plasma Zn and plasma total phospholipid FA composition, as well as to assess the effect of Zn fortified water on the plasma total phospholipid FA composition of rural Beninese school children aged between 6 and 10 years. Methods. In a 20-week double blind randomised controlled trial, Beninese school children from a low-income rural setting aged between 6 and 10 years (n = 185) were randomly assigned to receive either a 300ml daily portion of Zn-fortified filtered water delivering 2.8 mg Zn (Zn+filter) or non-fortified filtered water (Filter). Plasma total phospholipid FA composition was determined using capillary gas chromatography and plasma Zn (PZn) analysis by atomic absorption spectrometry. Associations between Zn and FA were examined at baseline. Furthermore, the effect of Zn fortification on plasma FA composition was analysed in the total group, as well as in the Zn deficient and sufficient children and in girls and boys separately. Results and discussion. At baseline, plasma Zn correlated positively with DGLA (r = 0.209; p = 0.010) and the DGLA:LA ratio (r = 0.327; p < 0.001). There was a significant inverse association between plasma Zn and linoleic acid (LA) (r = –0.229; p = 0.005) and the arachidonic: dihomo-γ-linolenic acid (ARA:DGLA) ratio (r = –0.257; p<0.001). At baseline, LA (p = 0.017), eicosapentaenoic acid (EPA) (p = 0.002), n-3 docosapentaenoic acid (DPA) (p = 0.020), adrenic acid (p = 0.010) and the ARA:LA ratio (p = 0.020) differed between boys and girls. In Zn sufficient boys, gamma-linolenic acid (GLA) was higher (p = 0.020) and the DGLA:GLA ratio tended to be higher (p = 0.059) than in Zn deficient boys. Zn fortification increased nervonic acid (p = 0.048) and tended to reduce LA (p = 0.068) in all children. Zn deficient children had a significantly higher nervonic acid composition (p = 0.019) after Zn fortification, whilst no significant effect was found in Zn sufficient children (p = 0.382). Fortification did not improve the plasma total phospholipid FA composition differently in boys and girls. Conclusion. The findings from this research therefore supports that the LA:DGLA (or DGLA:LA) ratio could be a possible biomarker for Zn status. Our results further demonstrated that Zn filtered fortified water had an effect on the plasma total phospholipid FA composition of children, and even more so in Zn deficient children, thereby indicating that elongation and desaturation might be improved by Zn. The plasma total phospholipid FA composition was affected more by Zn deficiency in boys than in girls. However, further research is required to fully confirm these results, as well to examine the underlying mechanisms that exist between Zn and FA in humans