Alpha linolenic acid (ALA) [18:3(n-3)] is an omega 3 essential fatty acids required by the body for health. Deficiency in ALA leads to inflammation, degeneration and disease. In humans, ALA is converted to a number of short lived hormones called eicosanoids that play an important role in a number of metabolic processes such as the modulation of inflammation, and cell signalling. Intermediates in the ALA metabolic pathway include eicosapentanoic acid (EPA) [20:5{n-3)] and docosahexanoic acid [22:6(n-3)]. Fatty fish such as mackerel, sardines, trout, salmon and tuna are a good source of EPA and DHA, and supplementation fish oils or the consumption of fatty fish has been shown to provide the same health benefits as consumption of ALA. Stearidonic acid [18:4(n-3)] is also intermediate in the ALA metabolic pathway, and is present in a number of foods.
Stearidonic acid is present mainly in sea food in concentrations of around 0.5 to 2 % of the total fatty acids, compared with EPA and DHA which contribute 15 to 20 %. Some fish, particularly mackerel have high concentrations of SDA (~7%). Sea weed (Undaria pinnatifida) also contains SDA (~0.7 to 1.9 mg/g dry weight). One of the problems with EPA is that it is both unstable (because of its high degree of unsaturation) and not suitable for vegetarians. Stearidonic acid is less unsaturated that EPA and therefore has a better chemical stability that makes it more suited to supplements that may require a long shelf life. In addition, SDA is present in a number of species of plant origin that makes it a viable alternative for vegetarians. Some of these plants are commercially farmed and available as supplements.
Plants from the Boraginaceae and Grossulariaceae, Carryophyllaceae and Primulaceae are unique amongst known terrestrial plants because they contain SDA. Borage (starflower) and echium plants from the Boraginaceae family contain relatively high amounts of SDA, with echium containing the most at 3.5 to 9 %. Species from the Grossulariaceae family such as black currant seed oil (Ribes nigrum) may contain 2 to 6 % SDA. Oils from the leaves of Carryophyllaceae, Primulaceae and Boraginaceae families contain the highest concentrations of SDA of any plant source based on dry weight. Concerns over pollutants (such as PCB and dioxin) in fish also make alternatives in the plant kingdom worthy of consideration. Black currant seed oils also contains gamma linoleic acid which is an intermediate in the omega-6 metabolic pathway, and so is a good source of both essential fatty acids.
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