| α-Linolenic acid | |
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Other names
ALA; Linolenic acid; cis,cis,cis-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid;[1] Industrene 120 |
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| Identifiers | |
| CAS number | 463-40-1 |
| PubChem | 5280934 |
| ChemSpider | 4444437 |
| UNII | 0RBV727H71 |
| DrugBank | DB00132 |
| ChEBI | CHEBI:27432 |
| ChEMBL | CHEMBL8739 |
| Jmol-3D images | Image 1 Image 2 |
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| Properties | |
| Molecular formula | C18H30O2 |
| Molar mass | 278.43 g mol−1 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid.[2] In physiological literature, it is given the name 18:3 (n−3).
α-Linolenic acid is a carboxylic acid with an 18-carbon chain and three cis double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the n end. Thus, α-linolenic acid is a polyunsaturated n−3 (omega-3) fatty acid. It is an isomer of gamma-linolenic acid, a polyunsaturated n−6 (omega-6) fatty acid.
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Alpha-linolenic acid was first isolated by Rollett[3] as cited in J. W. McCutcheon's synthesis in 1942,[4] and referred to in Green and Hilditch's 1930's survey.[5] It was first artificially synthesized in 1995 from C6 homologating agents. A Wittig reaction of the phosphonium salt of [(Z-Z)-nona-3,6-dien-1-yl]triphenylphosphonium bromide with methyl 9-oxononanoate, followed by saponification, completed the synthesis.[6]
Seed oils are the richest sources of α-linolenic acid, notably those of rapeseed (canola), soybeans, walnuts, flaxseed (linseed oil), perilla, chia, and hemp. α-Linolenic acid is also obtained from the thylakoid membranes of the green leaves of broadleaf plants (the membranes responsible for photosynthesis).[7] The α-linolenic acid itself is suitable for many cooking purposes, at least as much as other minimally suitable cooking oils (such as butter, to which it is thermally superior), as it can withstand temperatures up to 350 degrees F (177 degrees Celsius) for 2 hours.[8]
| Common name | Alternate name | Linnaean name | % ALA† | ref. |
|---|---|---|---|---|
| Chia | chia sage | Salvia hispanica | 64% | [9] |
| Kiwifruit seeds | Chinese gooseberry | Actinidia chinensis | 62% | [9] |
| Perilla | shiso | Perilla frutescens | 58% | [9] |
| Flax | linseed | Linum usatissimum | 55% | [9] |
| Lingonberry | cowberry | Vaccinium vitis-idaea | 49% | [9] |
| Purslane | portulaca | Portulaca oleracea | 35% | [9] |
| Sea buckthorn | seaberry | Hippophae rhamnoides L. | 32% | [10] |
| Hemp | cannabis | Cannabis sativa | 20% | [9] |
| Rapeseed | canola | Brassica napus | 10% | [2] |
| Soybean | soya | Glycine max | 8% | [2] |
| †average val | ||||
α-Linolenic acid, an n−3 fatty acid, is a member of the group of essential fatty acids (EFAs), so called because they cannot be produced within the body and must be acquired through diet. Most seeds and seed oils are much richer in an n−6 fatty acid, linoleic acid. Linoleic acid is also an EFA, but it, and the other n−6 fatty acids, compete with n−3s for positions in cell membranes and have very different effects on human health. (See Essential fatty acid interactions.)
α-Linolenic acid can only be obtained by humans through their diets because the absence of the required 12- and 15-desaturase enzymes makes de novo synthesis from stearic acid impossible. Eicosapentaenoic acid (EPA; 20:5, n−3) and docosahexaenoic acid (DHA; 22:6, n−3) are readily available from fish oil and play a vital role in many metabolic processes. These can also be synthesized by humans from dietary α-linolenic acid, but with an efficiency of only a few percent.[11] Because the efficacy of n−3 long-chain polyunsaturated fatty acid (LC-PUFA) synthesis decreases down the cascade of α-linolenic acid conversion, DHA synthesis from α-linolenic acid is even more restricted than that of EPA.[12][13]
Linoleic acid (LA; 18:2, n−6) is generally assumed to reduce EPA synthesis because of the competition between α-linolenic acid and LA for common desaturation and elongation enzymes.
Studies have found evidence α-linolenic acid is related to a lower risk of cardiovascular disease.[14][15]
A 2005 study found that daily administration of α-linolenic acid significantly reduced both self-reported anxiety, stress levels, and objective measured cortisol levels in college age students.[16]
A large 2006 study found no association between total α-linolenic acid intake and overall risk of prostate cancer.[17] Multiple studies[18][19] have shown a relationship between alpha-linolenic acid (ALA), which is abundant in linseed oil, and an increased risk of prostate cancer. This risk was found to be irrespective of source of origin (e.g. meat, vegetable oil).[20] A recent (2009) metastudy, however, found evidence of publication bias in earlier studies, and concluded that if ALA contributes to increased prostate cancer risk, the increase in risk is quite small.[21]
Research has also suggested a major neuroprotective effect of α-linolenic acid in in vivo models of both global ischemia and KA-induced epilepsy;[22] however, if sourced from flax seed oil, residues may have adverse effect due to its content of neurotoxic cyanogen glycosides and immunosuppressive cyclic nonapeptides.[23]
A 2011 longitudinal study of over 50,000 women, conducted at Harvard University, over a period of ten years, found that a higher intake of α-Linolenic acid (combined with a lower intake of linoleic acid) was positively associated with a significant reduction in depression in the same group (the same study also found that by contrast an intake of EPA and DPA found in fish oils did not reduce depression). [24]
For manufacturers to achieve desirable traits, such as texture, spreadability and mouth feel, as well as to increase shelf life of products, unsaturated vegetable oils are often hydrogenated. Hydrogenation involves reacting the oils with hydrogen gas under pressure and high heat with the aid of a catalyst such as platinum oxide. Fully hydrogenated fatty acids become saturated fatty acids, although as fats they are not suitable for use in food, as they are as hard as wax due to the chain lengths of the original unsaturated fatty acids in the vegetable oils. Instead, oils are often only partially hydrogenated. When partially hydrogenated, part of the unsaturated fatty acids become unhealthy trans fats.
Soybeans are the largest source of edible oils in the U.S., and 40% of soy oil production is partially hydrogenated.[25][26] The low oxidative stability of α-linolenic acid is one reason for producers deciding to partially hydrogenate soybean oil.[27]
Regulations forcing the listing or banning of trans fats have spurred the development of low-α-linolenic acid soybeans. These yield a more stable oil requiring hydrogenation in fewer products, and therefore providing trans fat-free alternatives for many applications, such as frying oil.[28] Several consortia are bringing low-α-linolenic acid soy to market. DuPont's effort involves silencing the FAD2 gene that codes for Δ6-desaturase, giving a soy oil with very low levels of both α-linolenic acid and LA.[29] Monsanto Company has introduced to the market Vistive, their brand of low α-linolenic acid soybeans, which is less controversial than most GMO Monsanto offerings, as it was created via conventional breeding techniques.
Dietary α-linolenic acid has been assessed for its role in cardiovascular health. Clinical benefits have been seen in some, but not all, studies. Still, a review in 2005 concluded "The weight of the evidence favors recommendations for modest dietary consumption of α-linolenic acid (2 to 3 g per day) for the primary and secondary prevention of coronary heart disease."[30]
α-Linolenic acid is the most abundant unsaturated component of several drying oils (e.g. perilla, walnut and linseed oils.)
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