Evening Primrose Oil Uses and Pharmacology
Essential fatty acids are important as cellular structural elements and as precursors of prostaglandins. Essential fatty acids are the biologically active parts of polyunsaturated fats and cannot be manufactured by the body. They must be provided by the diet in relatively large
amounts. 5 Recommended intake of linoleic acid and alpha-linolenic acid are 12 g and 1.1 g, respectively, for women 19 to 30 years of age.
In theory, the GLA provided by evening primrose oil can be converted directly to the prostaglandin precursor di-homo-gamma-linolenic acid (DGLA) and might be beneficial to people unable to metabolize cis-linoleic acid to GLA or with low dietary intake of cis-linoleic acid. However, this relationship was not proven in a pharmacokinetic study in healthy humans.
Premenstrual syndrome/Menopause-associated vasomotor symptoms
A number of reviews and randomized clinical trials suggest there is little evidence to support the use of evening primrose oil for menopausal vasomotor symptoms or premenstrual syndrome. A satisfactory meta-analysis of the available data has not yet been achieved, but a protocol has been published by the Cochrane Collaboration, the results of which are pending.
The North American Menopause Society does not support the use of evening primrose oil for hot flash relief given the lack of efficacy data.
Mastalgia
A few researchers suggest benefit from evening primrose oil in the management of cyclic mastalgia, but there is little evidence to support this. One randomized, controlled trial found no benefit of evening primrose oil over control.
Rheumatoid arthritis
A Cochrane review of randomized trials using evening primrose oil versus placebo suggests some benefit in using evening primrose oil for rheumatoid arthritis, despite the relative poor quality of the individual studies. A trend toward reduction of morning stiffness and joint tenderness as well as pain relief has been shown. The authors found the evidence to be sufficient to warrant further larger trials to provide conclusive results and define optimal dosage and duration of therapy. 28 These findings are supported by other reviews, especially with regard to effective duration of therapy.
A more recent randomized, double-blind, placebo-controlled study involving 90 patients with primary Sjorgen syndrome found no statistical significance in patient tiredness with a higher dosage after 6 months of therapy. Other studies, primarily in animals and healthy humans,
provide the theoretical rationale for the effect of GLA in inflammatory disease.
Multiple sclerosis
Despite a seemingly valid theoretical basis for the use of evening primrose oil in multiple sclerosis, there is a lack of evidence to substantiate its use and no new trials since the 1980s. A review of 3 trials suggested an effect with a slower progression of disability and improved relapse (severity and duration) scores, but a randomized, controlled trial, not included in the review, showed no effect.
Atopic dermatitis/Dermatologic disordersA number of reviews and randomized clinical trials suggest a lack of support for the use of evening primrose oil for atopic dermatitis. Many of the trials are of poor quality and have apparent issues of bias. While an earlier review suggested promising results, the most comprehensive meta-analysis to date was unable to establish efficacy. 3 A protocol seeking to assess the effects of oral evening primrose oil and borage oil for
treating the symptoms of atopic eczema has been published by the Cochrane Collaboration, the results of which are pending.
Other uses
Cardiovascular diseaseThere is no recent evidence to support older studies suggesting that evening primrose oil reduced platelet aggregation. An observational study suggests serum linoleic acid may protect against ischemic stroke. Despite limited older trials in humans and numerous studies using rats and rabbits, there are no recent randomized, controlled trials demonstrating a beneficial effect of evening primrose oil on cholesterol levels or serum lipids.
A more recent randomized, controlled trial found no effect on endothelial function or vascular tone with evening primrose oil supplementation.
Diabetic neuropathy
A review of 3 randomized, controlled trials suggested evening primrose oil might improve symptoms of diabetic neuropathy. Dosages in these trials ranged from 360 to 480 mg GLA daily. Few side effects were noted in these trials, and there was no increase in blood glucose levels.
Dyslexia/Brain development
Current interest in the use of evening primrose oil for enhancing intellectual performance in children is yet to be validated by rigorous research.Studies conducted in children with dyslexia suggest improved reading, spelling, and behavior, while a Cochrane systematic review and a long-term study (39 months) showed no long-term benefit in infants fed formula supplemented
with long-chain polyunsaturated fatty acids.
Eye conditions
Study results disagree as to the effect of evening primrose oil on dry eye syndrome, 31 , 53 and there is concern regarding high intake of linolenic and linolenic acid and the risk of cataract development.
Dosage
Evening primrose oil has been administered orally in clinical trials at doses between 6 and 8 g/day in adults and 2 and 4 g/day in children. The typical content of GLA in the oil is 8% to 10%.
Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking. Both linoleic and gamma-linolenic acid are normally present in breast milk, and it is reasonable to assume that evening primrose oil may be taken while breast-feeding.
Adverse Reactions
Evening primrose oil is suspected to lower the seizure threshold in epileptic patients.
Toxicology
Animal toxicological studies and extensive use of evening primrose oil over many years have revealed no data of concern. As a nutritional supplement, the maximum label-recommended daily dose of evening primrose oil is approximately 4 g, containing 300 to 360 mg GLA. There is little concern about the safety of evening primrose oil as a dietary supplement in the recommended dosage range.
