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Supplementation with Omega-6 Fatty Acids
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[2008 updates are highlighted in red]
| Description: |
Supplementation with omega-6 fatty acids is an approach that increases the intake of polyunsaturated fatty acids (PUFAs). Most studies of omega-6 fatty acid supplementation have used sunflower seed oil or evening primrose oil. Other dietary supplements that contain omega-6 fatty acids include flaxseed oil, borage seed oil, black currant seed oil, and spirulina (blue-green algae). |
| Rationale: |
As noted for the Swank diet (see above), epidemiological studies indicate that a high intake of PUFAs may be associated with a lower risk of developing MS. There are other findings that support the use of a diet enriched in omega-6 fatty acids. Some, but not all, studies have shown that the blood levels of PUFAs are decreased in people with MS. In addition, scientific studies show that in the body PUFAs are converted to compounds known as leukotrienes and prostaglandins. These compounds have anti-inflammatory effects and immune system-modulating effects that, on a theoretical basis, could be therapeutic for MS. |
| Evaluation: |
In the animal model of MS, disease severity is worsened by deficiencies in omega-6 fatty acids and lessened by supplementation with omega-6 fatty acids. In people with RRMS, three placebo-controlled clinical trials have evaluated supplementation with omega-6 fatty acids. In these studies, the treated group received sunflower seed oil, which contains an omega-6 fatty acid known as linoleic acid. In two of these studies, there was a significant decrease in the duration and severity of MS attacks. In the other study, there was not a therapeutic effect. A re-analysis of these three studies, for which not all of the original data was available, showed that people with mild disability had a statistically significant decrease in progression of disability and a statistically significant decrease in attack severity and duration; people with moderate-severe disability had no significant change in disability and a statistically significant decrease in attack severity and duration. In studies of people with progressive MS, omega-6 fatty acid supplementation has not been effective. Evening primrose oil, a dietary supplement that contains an omega-6 fatty acid known as gamma-linolenic acid, has not produced therapeutic effects in people with relapsing-remitting or progressive disease. |
| Risks: |
Supplementation with omega-6 fatty acids is usually well tolerated. The safety of long-term supplementation with omega-6 fatty acids has not been well studied. A concern has been raised that linoleic acid supplementation may increase the risk of some forms of cancer, but this has not been proven. Since supplementation with PUFAs may cause vitamin E deficiency, supplementation with vitamin E may be necessary. Evening primrose oil, and perhaps other gamma-linolenic acid-containing supplements (black currant seed oil, borage seed oil, spirulina), may rarely provoke seizures. Also, gamma-linolenic acid-containing supplements may have blood-thinning effects. Omega-6 fatty acid supplements may increase triglyceride levels and thus should be used with caution by people with elevated triglycerides. One specific supplement, borage seed oil, may contain liver toxins known as pyrrolizidine alkaloids. The safety of black currant seed oil has not been well studied. Spirulina products may contain heavy metals, bacteria, and other contaminants. The safety of omega-6 fatty acid supplementation in women who are pregnant or breastfeeding is not known. |
| Costs: |
Supplementation with omega-6 fatty acids is inexpensive. |
| Committee opinion: |
In the opinion of the Committee, omega-6 fatty acid supplementation is an inexpensive and generally well-tolerated approach that has produced suggestive therapeutic effects in trials with RRMS. Further studies are needed to determine if it is definitely effective. The safety and effectiveness of this approach in combination with disease-modifying medications (interferons, glatiramer acetate, mitoxantrone, and natalizumab) are not known.
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