Free Access
Reprod. Nutr. Dev.
Volume 45, Number 5, September-October 2005
Page(s) 581 - 597
Reprod. Nutr. Dev. 45 (2005) 581-597
DOI: 10.1051/rnd:2005047

Conversion of $\alpha$-linolenic acid to longer-chain polyunsaturated fatty acids in human adults

Graham C. Burdge and Philip C. Calder

Institute of Human Nutrition, University of Southampton, Southampton, UK

(Received 21 February 2005; accepted 7 April 2005)

Abstract - The principal biological role of $\alpha$-linolenic acid ($\alpha$LNA; 18:3n-3) appears to be as a precursor for the synthesis of longer chain n-3 polyunsaturated fatty acids (PUFA). Increasing $\alpha$LNA intake for a period of weeks to months results in an increase in the proportion of eicosapentaenoic acid (EPA; 20:5n-3) in plasma lipids, in erythrocytes, leukocytes, platelets and in breast milk but there is no increase in docosahexaenoic acid (DHA; 22:6n-3), which may even decline in some pools at high $\alpha$LNA intakes. Stable isotope tracer studies indicate that conversion of $\alpha$LNA to EPA occurs but is limited in men and that further transformation to DHA is very low. The fractional conversion of $\alpha$LNA to the longer chain n-3 PUFA is greater in women which may be due to a regulatory effect of oestrogen. A lower proportion of $\alpha$LNA is used for $\beta$-oxidation in women compared with men. Overall, $\alpha$LNA appears to be a limited source of longer chain n-3 PUFA in humans. Thus, adequate intakes of preformed long chain n-3 PUFA, in particular DHA, may be important for maintaining optimal tissue function. Capacity to up-regulate $\alpha$LNA conversion in women may be important for meeting the demands of the fetus and neonate for DHA.

Key words: n-3 polyunsaturated fatty acids / humans / $\alpha$-linolenic acid / metabolism

Corresponding author: Graham C. Burdge

© INRA, EDP Sciences 2005