Oenothera biennis, commonly known as evening primrose, is a good source of a type of omega-6 fatty acid known as gamma-linolenic acid. This type of fatty acid may be useful for reducing high blood pressure, according to the University of Maryland Medical Center. Herbal remedies can cause side effects and interact with medications, so the UMMC recommends only taking these supplements under the supervision of a qualified health care provider.
Significance
Omega-6 fatty acids are essential fatty acids, meaning they are necessary for health, but the body cannot produce them. People must obtain omega-6 fatty acids through diet or supplements. Gamma-linolenic acid, or GLA, is an important fatty acid, because while some omega-6 fatty acids promote inflammation, GLA actually decreases inflammation, explains the UMMC.
GLA and Blood Pressure in Animals
Animal research indicates that GLA decreases blood pressure, according to the UMMC. For instance, a study published in the May 1984 issue of Proceedings of the Society of Experimental Biology and Medicine investigated the effects of GLA on rats with stress-induced hypertension. Animals receiving .018 mg of GLA per hour had lower systolic blood pressure than animals that did not receive supplements, and animals receiving .040 mg of GLA per hour had an even smaller rise in systolic blood pressure. The authors noted that GLA did not affect blood pressure in unstressed rats.
GLA and Blood Pressure in Humans
GLA may help to lower high blood pressure by itself or in combination with the omega-3 fatty acids eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA, found in fish oil. In one study cited by the UMMC, participants with intermittent claudication took GLA and EPA supplements to reduce pain in the legs caused by blood vessel blockages. Participants taking these supplements experienced reduced systolic blood pressure compared to those taking a placebo. However, the UMMC cautions that research results in total do not show consistent blood pressure effects associated with GLA.
Other Benefits
Taking GLA supplements such as evening primrose oil may decrease nerve pain in people with diabetic neuropathy, according to the UMMC. Evening primrose oil also may help to relieve symptoms of rheumatoid arthritis, including pain, swelling and morning stiffness. Research results are mixed on whether evening primrose oil reduces eczema symptoms, according to the UMMC. The UMMC cites research with women over 65 with osteoporosis, wherein those taking both EPA and GLA over three years experienced less bone loss than those taking a placebo.
Side Effects and Interactions
Some people who take evening primrose oil experience occasional headaches, abdominal pain, nausea and loose stools. The U.S. National Institutes of Health cautions anyone taking blood pressure medications to consult with a health care provider before taking evening primrose oil, since combining the two could lead to abnormally low blood pressure. Evening primrose oil also may increase blood-thinning effects of nonsteroidal anti-inflammatory drugs, anticoagulants and antiplatelet medications.
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