α‐Linolenic acid metabolism in adult humans: the effects of gender and age on conversion to longer‐chain polyunsaturated fatty acids

This review summarises and evaluates current knowledge of α-linolenic acid (αLNA) metabolism in adult humans. The principal biological role of αLNA appears to be as a precursor for the synthesis of longer-chain n-3 polyunsaturated fatty acids (PUFA). Stable isotope tracer studies indicate that conversion of αLNA to eicosapentaenoic acid (EPA) occurs but is limited in men and that further transformation to docosahexaenoic acid (DHA) is very low. A lower proportion of αLNA is used for β-oxidation in women compared with men, while the fractional conversion to the longer-chain n-3 PUFA is greater, possibly due to the regulatory effects of oestrogen. Increasing αLNA intake for a period of weeks results in an increase in the proportion of EPA in plasma lipids, circulating cells and breast milk, but there is no increase in DHA, which may even decline in some pools at high αLNA intakes. Overall, αLNA appears to be a limited source of longer-chain n-3 PUFA in man, and so adequate intakes of preformed long-chain n-3 PUFA, in particular DHA, may be important for maintaining optimal tissue function. The capacity to up-regulate αLNA transformation in women may be important for meeting the demands of the foetus and neonate for DHA.