Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)?
Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)?
Year: 1998
Authors: H Gerster.
Publication Name: Int. J. Vitam. Nutr. Res.
Publication Details: Volume 68; Number 3; 159.
Abstract:
In this review paper, the author indicates that a diet containing 2-3 portions of fatty fish per week, which corresponds to an intake of 1.25 g EPA and DHA per day, has been officially recommended on the basis of epidemiological findings to help reduce and prevent cardiovascular and inflammatory diseases. ALA, found in vegetable oils such as FS and CO, is used by the body partly as a source of energy. In addition, ALA can serve as a precursor for EPA and DHA; however, inconsistency exists in the literature as to the degree of this conversion. Ten human studies in which FS or CO was fed as a source of ALA are presented in the paper. These human studies reported that whereas a certain, though restricted, conversion of high doses of ALA to EPA occurs, conversion to DHA appears to be restricted. The use of ALA labeled with radioisotopes suggests that with a background diet high in SFAs, conversion of ALA is approximately 7% for EPA and 3.8% for DHA. The effects of LA/ALA ratio on the conversion of ALA to longer chain n-3 PUFAs have been assessed in a number of studies. A review of these publications shows that in diets rich in LA, ALA conversion to EPA and DHA is reduced by 40 to 50% due to competition between LA and ALA for common desaturase and elongation enzymes. In addition, dietary LA inhibits the uptake of ALA. The author suggests that based upon these observations, the dietary ratio of n-6:n-3 PUFAs should not exceed 4-6. This is often difficult in a Western diet that is typically high in sources of LA. Numerous studies have shown that ALA conversion to DHA is critical since the long-chain metabolite has an autonomous function in the brain, retina and spermatozoa where it is the most prominent fatty acid. In neonates, DHA deficiency is associated with visual impairment, abnormalities in the electroretinogram and delayed cognitive development. In adults, the potential role of DHA in neurological function is under investigation. Regarding cardiovascular risk factors, DHA has also been shown to reduce serum TGs. The author concludes that findings to date indicate that future attention will need to be focused on the adequate provision of DHA either as preformed in the diet or in part through conversion from ALA.
