GLA (gamma-linolenic acid) is one of the two main types of essential fatty acids. These are "good" fats that are as necessary for your health as vitamins. Specifically, GLA is an omega-6 fatty acid. (For more information on the other major category of essential fatty acids, omega-3, see the article onfish oil.)

The body uses essential fatty acids to make various prostaglandins and leukotrienes. These substances influence inflammation and pain; some of them increase symptoms, while others decrease them. Taking GLA may swing the balance over to the more favorable prostaglandins and leukotrienes, making it helpful for diseases that involve inflammation.

There is some evidence that GLA may be helpful for diabetic neuropathy. The supplement is widely used in the UK and other parts of Europe to treateczema and cyclic mastalgia (a condition marked by breast pain associated with the menstrual cycle). Current evidence, however, suggests that it may not help. There are many other proposed uses of GLA based on fairly weak evidence.

The body ordinarily makes all the GLA it needs from linoleic acid, an omega-6 essential fatty acid found in many foods. In certain circumstances, however, the body may not be able to convert linoleic acid to GLA efficiently. These include advanced age, diabetes, high alcohol intake, eczema, cyclic mastitis, viral infections, excessive saturated fat intake, elevated cholesterol levels, and deficiencies of vitamin B 6, zinc, magnesium, biotin, or calcium.1-5 In such cases, taking GLA supplements may make up for a genuine deficiency.

Very little GLA is found in the diet. Borage oil is the richest supplemental source (17% to 25% GLA), followed by black currant oil (15% to 20%) and evening primrose oil (7% to 10%). Borage and evening primrose are the most common sources used in studies.

It is commonly stated that people require a certain optimum ratio of omega-3 to omega-6 fatty acids in the diet; however, there is no real evidence that this is true, and some evidence that it is false.91