Evening Primrose Oil (EPO) is made from the seeds of the herb Oenothera biennis that grows wild in arid environments such as sand dunes. True to its name, evening primrose flowers (bright yellow) open in the evening and fade in bright sunlight. First documented medicinally in England, evening primrose oil is most commonly used for relieving premenstrual syndrome, fibrocystic breasts, and menopausal symptoms such as hot flashes.
It appears that evening primrose oil may be a useful alternative to prescription medication for symptoms of PMS, especially breast pain associated with the menstrual cycle. Perhaps the most promising use for evening primrose oil is its cardioprotective effect delivered by its profile of anti-inflammatory fatty acids.
Sixty to 80% of evening primrose oil is the essential (not produced by the body) fatty acid, linoleic acid. Gamma linoleic acid (GLA) is synthesized by the body from linoleic acid and comprises 8-14% of the oil. GLA is a precursor of prostaglandin E1 (PGE1) - the deficiency of which has been documented in some women with premenstrual syndrome (PMS) and cyclical breast pain (Bendich 2000, Bordoni et al. 1987). Since decreased levels of PGE1 can increase the pain-inducing effects of the hormone prolactin on breast tissue, it is thought that low PGE1 levels may be a primary cause of many of the symptoms associated with PMS (Cheung 1999).
In addition to its applications for specific detrimental effects of the menstrual cycle, theories for non-gender related uses for evening primrose oil are prevalent. PGE1 has beneficial anti-inflammatory, blood-thinning and vasodilating properties (Dirks et al. 1998). Also, since GLA increases PGE1 levels, supplementation with evening primrose oil could theoretically provide benefits in rheumatoid arthritis and coronary artery disease (Laivuori et al. 1993). Because essential fatty acids are claimed to have positive effects on certain skin diseases, supplementation with evening primrose oil, comprised mostly of essential fatty acids, could also alleviate eczema and dermatitis. Finally, people with GLA deficiencies are thought to produce more fat in their bodies – so theories abound for evening primrose oil supplements to promote fat loss.
Most scientific literature related to evening primrose oil supplementation involves its use for promoting well-being during the menstrual cycle. In two controlled studies, subjects received 4-6 grams of evening primrose oil or placebo for 3-4 months – but neither trial was able to demonstrate a significant benefit of the supplements (Horrobin 1983, Horrobin 1993). It is worth noting, however, that other placebo-controlled studies have shown significant benefits of supplementation with evening primrose oil, but only after 6 months of treatment (Chenoy et al. 1994, Collins et al. 1993). In the treatment of cyclic breast pain, evening primrose oil has been found to be more effective than placebo (44% versus 19%, respectively) and when compared to treatment with the prescription drugs (bromocriptine and danazol), evening primrose oil was as effective as bromocriptine, but less effective than danazol in alleviating breast pain (Huntley and Ernst 2003). In one well-controlled study to evaluate the use of evening primrose oil for the relief of hot flashes associated with menopause, 56 women were treated for 6 months with either 4 grams of evening primrose oil, or placebo – but no significant benefits were attributed to taking evening primrose oil for treatment of menopausal symptoms (Huntley and Ernst 2003).
Perhaps the most convincing evidence for supplementing with evening primrose oil involves its use in those with coronary artery disease. A study in 10 patients with high cholesterol levels showed that 3.6 grams of evening primrose oil taken daily for 8 weeks significantly decreased LDL (“bad”) cholesterol by 9% (Cern et al. 1993). However, for patients with high triglyceride and cholesterol levels, no such reductions occurred. In a double-blind crossover study in men taking either fish oil alone or fish oil plus evening primrose oil, the combination lead to a significant 12% decrease in atherogenic markers, whereas fish oil alone lead to a nonsignificant 6% decrease in the same markers (Brzeski et al. 1991).
There are many other claims for the use of evening primrose oil, though the scientific findings are rather disappointing. In a 6-week, double-blind, placebo-controlled study of 58 children who required treatment with topical skin steroids for atopic dermatitis (22 of which also had asthma), no significant difference was found between the placebo and the evening primrose oil group (Schafer and Kragballe 1991). Likewise, no effect was seen in terms of asthma symptoms. In a 24-week, double-blind, placebo-controlled study of 39 patients with chronic hand dermatitis (Whitaker et al. 1996), no therapeutic value was shown following 600mg of daily GLA supplements (compared to placebo). No scientific evidence is available to support any benefit of evening primrose oil in alleviating rheumatoid arthritis or in aiding weight loss.
Evening primrose oil appears to be quite safe. Potential adverse effects include gastrointestinal upset and headache. Because evening primrose oil hinders platelet aggregation, this supplement may increase the anti-coagulant effect of drugs such as warfarin. Therefore, anyone taking anti-coagulants should consult with his/her personal physician before taking evening primrose oil. The most common dose of evening primrose oil is 1-4 grams per day with approximately 10% GLA.
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EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS