GLA

Gamma-linolenic acid is a polyunsaturated fatty acid of the omega-6 family, described chemically as an eighteen-carbon chain bearing three double bonds and designated 18:3 (n-6). It is an isomer of the more familiar alpha-linolenic acid but differs in the position of its double bonds and in its biological role. In most diets it is only a minor fatty acid, since just a few plant oils contain it in appreciable amounts.

The richest dietary sources of GLA are specialized seed oils: borage, or starflower, oil is the most concentrated, followed by evening primrose oil and blackcurrant seed oil, with smaller amounts in hemp seed oil and the cyanobacterium spirulina ^[3]. The human body can also synthesize GLA from linoleic acid, an essential fatty acid abundant in vegetable oils, through the action of the enzyme delta-6-desaturase ^[1]. This conversion is slow and rate-limiting in people, and it may be further reduced by aging, diabetes, or other factors, which forms part of the rationale for supplying GLA directly ^[1]. Once formed, GLA is rapidly elongated in the body to dihomo-gamma-linolenic acid (DGLA).

Interest in GLA rests largely on the fate of DGLA in the body ^[2]. DGLA can be converted into series-1 eicosanoids, such as prostaglandin E1, which tend to have anti-inflammatory and vasodilatory effects, and it can compete with arachidonic acid, thereby limiting the formation of the more pro-inflammatory series-2 prostaglandins and series-4 leukotrienes ^[2]. On this basis, GLA-rich oils have been tested in a range of inflammatory and skin conditions, including atopic dermatitis, rheumatoid arthritis, diabetic neuropathy, and breast pain, as well as in disorders of essential-fatty-acid metabolism ^[1][2][3]. Results have been mixed: some randomized trials suggest modest benefit in conditions such as rheumatoid arthritis, whereas the evidence for eczema has been largely disappointing ^[2][3].

The therapeutic study of GLA is associated in particular with the researcher David Horrobin and the company Efamol, which promoted evening primrose oil from the 1980s ^[1]. In the United Kingdom, medicines based on evening primrose oil were once licensed for eczema, but these authorizations were withdrawn in 2002 after reviews concluded that the evidence of benefit was insufficient. Today GLA-containing oils are sold chiefly as over-the-counter dietary supplements rather than as licensed medicines, and they are generally regarded as well tolerated, with mild digestive upset being the most common complaint.

Generally well tolerated, with mild GI upset or headache the most common complaints. There is a theoretical concern about lowering seizure threshold in susceptible people, so those with seizure disorders should be cautious. Its mild antiplatelet potential means care with blood thinners, and very high or unbalanced omega-6 intake is best avoided by pairing with omega-3s.