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Conversion of alpha-linolenic acid to eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in young women

Burdge, G.C., Wootton, S.A.. (2002) British Journal of Nutrition 88 411-420 

Web URL: View this and related abstracts via PubMed here


The extent to which women of reproductive age are able to convert the n-3 fatty acid alpha-linolenic acid (ALNA) to eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) was investigated in vivo by measuring the concentrations of labelled fatty acids in plasma for 21 d following the ingestion of 13C ALNA (700 mg).

13C ALNA excursion was greatest in cholesteryl ester (CE) (224 (sem 70) micromol/l over 21 d) compared with triacylglycerol (9-fold), non-esterified fatty acids (37-fold) and phosphatidylcholine (PC, 7-fold). EPA excursion was similar in both PC (42 (sem 8) micromol/l) and CE (42 (sem 9) micromol/l) over 21 d.

In contrast both 13C DPA and 13C DHA were detected predominately in PC (18 (sem 4) and 27 (sem 7) micromol/l over 21 d, respectively). Estimated net fractional ALNA inter-conversion was EPA 21 %, DPA 6 % and DHA 9 %. Approximately 22 % of administered 13C ALNA was recovered as 13CO2 on breath over the first 24 h of the study. These results suggest differential partitioning of ALNA, EPA and DHA between plasma lipid classes, which may facilitate targeting of individual n-3 fatty acids to specific tissues.

Comparison with previous studies suggests that women may possess a greater capacity for ALNA conversion than men. Such metabolic capacity may be important for meeting the demands of the fetus and neonate for DHA during pregnancy and lactation. Differences in DHA status between women both in the non-pregnant state and in pregnancy may reflect variations in metabolic capacity for DHA synthesis.


This study found that in young women, conversion of the short-chain omega-3 fatty acid alpha-linolenic acid (ALA - found in some plant and seed oils such as flax, hemp or canola) into the long-chain omega-3 most important for brain and body health (EPA and DHA, found in fish and seafood) was very limited.

Less than 20% of dietary ALA was converted to EPA, and less than 10% to DHA.  

Given the critical importance of EPA and DHA for brain function - and especially the critical importance of DHA for normal brain development in pregnancy and early life - these findings support the idea that women following purely vegetarian or vegan diets would do well to consider supplementing with DHA from algal sources, especially before starting pregnancy. 

A separate study showed that this conversion of ALA to long-chain omega-3 was even poorer in young men - who made no detectable DHA at all from dietary ALA. See: