People with eczema, or dermatitis, may find relief from a surprising source: the dainty evening primrose (Oenothera biennis). The active phytochemical in evening primrose oil, gamma-linolenic acid (GLA), is one of the best-known substances for restoring and maintaining healthy skin.
GLA is a storage lipid, one that stores the food energy for the primrose seed to consume while sprouting. In relation to the human body, GLA is called a polyunsaturated fatty acid, or PUFA. PUFAs must be consumed in the diet because they can’t be made directly by the body. Linoleic acid (LA) is another PUFA related to GLA and often a precursor to it. In a healthy body, LA is converted to GLA.
LA is required for proper body functioning, and is thus classified as an essential fatty acid (EFA)—a distinction GLA doesn’t yet officially have. But GLA should be considered among the EFAs—at least for people with dermatitis, also called eczema. Studies on individuals with eczema have shown that they lack the ability to convert LA to GLA.
Which plants have GLA?
Most plants don’t contain significant levels of GLA, making the GLA-rich seed oil of evening primrose a valuable commercial resource. Although the GLA content of evening primrose oil is only about half that of borage seed (Borago officinalis), black currant (Ribes nigrum), and many fungal oils, it is considered a superior source of GLA for pharmacological use because it appears to be more bioavailable—that is, the body seems to process and benefit from it more readily than it does other sources. This has been demonstrated in several laboratory experiments where rats were fed diets containing equal quantities of GLA from evening primrose, black currant, borage, or fungal oils. The rats fed GLA from evening primrose produced the highest amount of certain anti-inflammatory biochemicals derived from GLA.
In other trials involving both humans and animals, evening primrose was also found to be more effective than borage, black currant, or fungal oils for lowering blood pressure, cholesterol, and platelet aggregation (clumping that plays a role in clotting).
Why does the body “prefer” GLA from evening primrose oil? All edible fats are called triglycerides because they have three fatty acids attached to one glycerol molecule. GLA-containing oils must be digested and metabolized just like any other dietary fat in order for the GLA to be used. Evening primrose oil has a simpler composition than the oil from other sources, and it contains a larger percentage of triglycerides composed of only GLA and LA. It’s thought that these two factors allow it to be more efficiently metabolized.
Reversing the deficiency
A deficiency of PUFAs in the diet may cause scaly dermatitis and skin lesions. The symptoms—red, itchy, scaly skin—bear a similarity to atopic eczema. Atopic means that the eczema is caused wholly or in part by a genetically based allergic condition.
It was once believed that large quantities of LA could cure atopic eczema. Research indicates that this type of eczema probably is caused by the body’s impaired ability to convert LA to its derivatives such as GLA, so prescribing large quantities of LA for treatment no longer makes sense. However, if atopic eczema patients receive only 2 to 6 g of evening primrose oil, a ready source of GLA, there is a dramatic clinical improvement in their skin.
Andreassi, M., et al. “Efficacy of gamma-linolenic acid in the treatment of patients with atopic dermatitis.” Journal of International Medical Research 1997, 2:266–274.
Gerster, H. “Can adults adequately convert a-linolenic acid (18:n–3) to eicosapentaneoic acid (20:5n–3) and docosahexanoic acid (22:6n–3)?” International Journal of Vitamin and Nutrition Research 1998, 68:159–173.
C. Leigh Broadhurst holds a doctorate in geochemistry and is a nutrition consultant in Clovery, Maryland.