GLA is categorized as an n−6 fatty acid, meaning that the first double bond on the methyl end is the sixth bond. In physiological literature, GLA is designated as 18:3. GLA is a carboxylic acid with an 18-carbon chain and three cis double bonds. It is an isomer of α-linolenic acid, which is a polyunsaturated n−3 fatty acid, found in rapeseedcanola oil, soybeans, walnuts, flax seed, perilla, chia, and hemp seed.
History
GLA was first isolated from the seed oil of evening primrose. This herbal plant was grown by Native Americans to treat swelling in the body. In the 17th century, it was introduced to Europe and became a popular folk remedy, earning the name king's cure-all. In 1919, Heiduschka and Lüft extracted the oil from evening primrose seeds and described an unusual linolenic acid, which they name γ-. Later, the exact chemical structure was characterized by Riley. Although there are α- and γ- forms of linolenic acid, there is no β- form. One was once identified, but it turned out to be an artifact of the original analytical process.
Dietary sources
GLA is obtained from vegetable oils such as evening primrose oil, blackcurrant seed oil, borage seed oil, and hemp seed oil. GLA is also found in varying amounts in edible hemp seeds, oats, barley, and spirulina. Normal safflower oil does not contain GLA, but a genetically modified GLA safflower oil available in commercial quantities since 2011 contains 40% GLA. Borage oil contains 20% GLA, evening primrose oil ranges from 8% to 10% GLA, and black-currant oil contains 15-20%. It also constitutes 12.23% of the fats from the fruit of the durian species Durio graveolens. The human body produces GLA from linoleic acid. This reaction is catalyzed by Δ6-desaturase, an enzyme that allows the creation of a double bond on the sixth carbon counting from the carboxyl terminus. LA is consumed sufficiently in most diets, from such abundant sources as cooking oils and meats. However, a lack of GLA can occur when there is a reduction of the efficiency of the D6D conversion or in disease states wherein there is excessive consumption of GLA metabolites.
Health and medicine
GLA has been promoted as medication for a variety of ailments including breast pain and eczema, in particular by David Horrobin, whose marketing of evening primrose oil was described by The BMJ as ethically dubious - the substance was likely to be remembered as "a remedy for which there is no disease". In 2002 the UK's Medicines and Healthcare products Regulatory Agency withdrew marketing authorisations for evening primrose oil as an eczema remedy. However, more recently, topical application of borage seed oil has been shown to reduce the symptoms of atopic dermatitis in a double-blind, placebo-controlled clinical trial.
