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α-Linolenic acid

Lipidomics Gateway (24 August 2011) [doi:10.1038/lipidmaps.2011.23]

Most studied as the precursor fatty acid of the n-3 polyunsaturated fatty acid family, this lipid might mediate biological effects independent of its long chain metabolites.

The structure of α-linolenic acid (all-cis-9,12,15-octadecatrienoic acid). Visit α-linolenic acid in the LIPID MAPS structure database for more molecular information.

With the first of its three cis double bonds located three carbons from the omega (n) end of the fatty acid chain, the 18-carbon α-linolenic acid (ALA, structurally known as all-cis-9,12,15-octadecatrienoic acid) belongs to the n-3 class of polyunsaturated fatty acids (PUFAs). ALA is an essential fatty acid and must therefore be obtained through the diet — mammals lack the appropriate enzymes to generate it de novo. Although ALA can be obtained from the thylakoid membranes of photosynthesizing plants, the predominant dietary source is seed oils, especially those derived from flaxseed, walnuts, soybeans, rapeseed, hemp, perilla and chia.

ALA is considered the parent of the n-3 PUFA family, as it can be converted, through a series of alternating desaturation and elongation steps, to long chain PUFAs — most notably eicosapentaenoic acid (EPA) and docohexaenoic acid (DHA). This conversion shows limited efficiency, however, so EPA and DHA must instead be obtained from the diet, mainly from oily fish. The health benefits associated with consuming n-3-rich-foods are well documented, particularly for chronic diseases such as cardiovascular disease, cancer and insulin resistance, but are largely attributed to EPA and DHA; data relating to a role for ALA are limited and inconsistent 1 2 . However, because ALA comprises the main dietary n-3 PUFA for many individuals, especially those on a Western diet, and is poorly converted to EPA and DHA, the possibility that ALA might mediate biological effects independent of its conversion to long chain metabolites has been raised 2 .

ALA, as well as being a precursor for EPA and DHA, can be metabolized by β-oxidation 3 , and also undergoes carbon recycling for new lipid synthesis 4 . Furthermore, as an isomer of the n-6 PUFA metabolic precursor γ-linoleic acid, ALA — and other n-3 PUFAs — competes with n-6 PUFAs not only for the same set of metabolic enzymes, but also for incorporation into membranes. Increased levels of n-3 PUFAs might therefore affect membrane fluidity and the function of receptors and other membrane-associated proteins 1 . Indeed, ALA supplementation has been reported to increase membrane fluidity 5 . Unlike EPA and DHA, however, which alter the function of membrane rafts and caveolae, the effect of ALA on these distinct lipid microdomains has yet to be determined 6 . Competition with n-6 PUFAs is thought to contribute considerably to the anti-inflammatory effects of n-3 PUFAs, by decreasing the synthesis of arachidonic acid and its inflammatory n-6 eicosanoid derivatives. More specifically, ALA also reduces the levels of inflammation-associated adhesion molecules 7 and can downregulate the expression of pro-inflammatory genes through the suppression of nuclear factor κB and activation of peroxisome proliferator-activated receptors 8 .

ALA might confer health benefits through these, and possibly other, mechanisms. Like EPA and DHA, ALA consumption is associated with a decreased risk of cardiovascular disease, potentially by affecting aspects of cardiac function as well as lowering cholesterol levels 1 . ALA also reportedly reduces the risk of insulin resistance through an anti-oxidant function as well as by promoting membrane fluidity 2 . Consistent evidence for an anti-carcinogenic role is, however, lacking 2 . Numerous other benefits of ALA have been reported, prompting the need for thorough research to clarify the benefits, and potential adverse effects, of ALA to human health.

Related articles

Eicosapentaenoic acid

This nutritionally important polyunsaturated fatty acid is found almost exclusively in oily fish. It has beneficial cardiovascular and anti-inflammatory effects, and may offer therapeutic potential for a range of diseases.

Docosahexaenoic acid

An omega-3 fatty acid that is important for proper brain function.

Katrin Legg

- Copyright © 2011 Nature Publishing Group, a division of Macmillan Publishers Limited; used with permission


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    N. Engl. J. Med. 364, 2439-2450 (2011). doi:10.1056/NEJMra1008153

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    Lipids In Health and Disease 8, 33 (2009). doi:10.1186/1476-511X-8-33

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  5. Dabadie, H., Motta, C., Peuchant, E., LeRuyet, P. & Mendy, F. Variations in daily intakes of myristic and alpha-linolenic acids in sn-2 position modify lipid profile and red blood cell membrane fluidity.

    Br. J. Nutr. 96, 283-289 (2006). doi:10.1079/BJN20061813

  6. Fan, Y.Y., McMurray, D.N., Ly, L.H. & Chapkin, R.S. Dietary (n-3) polyunsaturated fatty acids remodel mouse T-cell lipid rafts.

    J. Nutr. 133, 1913-1920 (2003).

  7. Thies, F. et al. Influence of dietary supplementation with long-chain n-3 or n-6 polyunsaturated fatty acids on blood inflammatory cell populations and functions and on plasma soluble adhesion molecules in healthy adults.

    Lipids 36, 1183-1193 (2001). doi:10.1007/s11745-001-0831-4

  8. Zhao, G., Etherton, T.D., Martin, K.R., Vanden, H.J.P., Gillies, P.J., West, S.G. & Kris-Etherton, P.M. Anti-inflammatory effects of polyunsaturated fatty acids in THP-1 cells.

    Biochem. Biophys. Res. Commun. 336, 909-917 (2005). doi:10.1016/j.bbrc.2005.08.204

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