As essential fatty acids, the omega-6 series are generally necessary for stimulation of growth, maintenance of skin and hair growth, regulation of metabolism, lipotropic activity, and maintenance of reproductive performance. The omega-6 oil linoleic acid is specifically required to maintain the integrity of the epidermal water barrier of the skin. Researchers believe they play an important role in reducing the risk of many chronic degenerative diseases such as heart disease, cancer, and stroke. Yet experts estimate that up to 80% of Americans consume an insufficient quantity of essential fatty acids.

The omega-6 fatty acids have been shown to improve nerve conduction and prevent neuropathy in diabetics. One animal study has suggested that the combination of gamma-linolenic acid (GLA) of the omega-6 series and ascorbate is particularly advantageous.

GLA has been shown to have an anti-inflammatory effect in humans and may play a role in treating conditions such as rheumatoid arthritis. Corroborated studies suggest that GLA is unique among the omega-6 series in suppressing tumor growth and metastasis. It has been shown to inhibit both motility and invasiveness of human colon cancer, breast cancer, and melanoma cells.

Recent animal research has suggested that omega-6 fatty acids can be beneficial in senile osteoporosis because it enhances absorption and retention of calcium. They also can be efficacious in vasodilation, lowering of blood pressure, and the prevention of atherosclerosis. Arachidonic acid of the omega-6 series is particularly important in normal brain function.

The optimal ratio of omega-6 oils to omega-3 oils should be 4:1. However, the American diet provides more than 10 times the needed amount of omega-6 fatty acids. This is because they are the primary fatty acids added to most processed foods and are commonly used cooking oils. However, consumption of refined and adulterated fats and oils inhibit the body's ability to use the essential fatty acids it consumes.

Sources of omega-6 fatty acids are plant seed oils, including evening primrose, black currant, borage, and fungal oils. Gamma-linolenic acid (GLA) is found in human milk and, in small amounts, in a wide variety of common foods, particularly organ meats. Linoleic acid is found in polyunsaturated vegetable oils, particularly sunflower oil, safflower oil, corn oil, and soybean oil. Arachidonic acid is found in egg yolk, organ meats, and other animal-based foods.

The omega-6 essential, polyunsaturated fatty acids are derived from linoleic acid and include gamma-linoleic acid, dihomo-gamma-linolenic acid (which converts to the desirable prostaglandin E₁ series) and arachidonic acid (which converts to the unfavorable series 2 prostaglandin).

The essential fatty acids are vitamin F, yet the Food and Drug Administration prohibits the term "vitamin F" for advertising purposes because of problems with foods such as french fries being advertised as "vitamin enriched" because they were fried in oil.

Evening primrose oil, black currant seed oil, borage oil, borage oil capsules, soybean oil, safflower oil, sunflower oil, corn oil

• Rheumatoid arthritis: GLA may reduce inflammation by suppressing T-cell proliferation and activation.
• Diabetes: Omega-6 fatty acid supplementation assists nerve function and helps prevent nerve disease in diabetics.
• Cancer: GLA may suppress tumor growth and metastasis, particularly in colon cancer, breast cancer, and melanoma.
• Heart disease: GLA may prevent heart disease by inhibiting plaque formation, vasodilation, and lowering blood pressure.
• Eyes: GLA is beneficial in Sjogren's syndrome and may be useful in other dry-eye conditions.

Supplementation may alleviate some of the symptoms of aging, alcoholism, atopic dermatitis, osteoporosis, and premenstrual syndrome.

• There is no Recommended Dietary Allowance (RDA).
• The recommended dosage for rheumatoid arthritis is 1.4 g per day of GLA.
• Supplementation with 480 mg of GLA per day for diabetes is recommended.
• Studies have shown that up to 2.8 g of GLA per day is well tolerated.

A healthy person eating a typical diet should reduce consumption of refined fats and increase consumption of the essential fatty acids. Omega-6 oils are far more available through dietary sources than omega-3 oils.

Dietary sources of omega-6 acids appear to be completely nontoxic.

Rats receiving cardiac allografts that were fed a diet high in omega-6 polyunsaturated fatty acids had a significantly prolonged median graft survival rate (14.5 days) compared to animals fed either lab chow or a diet high in monounsaturated fatty acids and saturated fat (Haw et al. 1995). The group treated with omega-6 had significantly higher myocardial blood flow after cyclosporine administration than the group fed the diet of saturated fat. Omega-6 fatty acids exhibited immunosuppressive effects because lymphocyte responses were suppressed to a greater extent in animals treated with these fatty acids.

Bolton-Smith C, Woodward M, Tavendale R. Evidence for age-related differences in the fatty acid composition of human adipose tissue, independent of diet. Eur J Clin Nutr. 1997;51(9):619-624.

Brown NA, Bron AJ, Harding JJ, Dewar HM. Nutrition supplements and the eye. Eye. 1998; 12(pt. 1): 127-133.

Ensminger AH, Ensminger ME, Konlande JE, Robson JRK. Foods & Nutrition Encyclopedia. 2nd ed. Boca Raton, Fla: CRC Press, Inc.; 1994:684-708.

Fan YY, Chapkin RS. Importance of dietary gamma-linolenic acid in human health and nutrition. J Nutr. 1998; 128(9): 1411-1414.

Garrison RH Jr, Somer E. The Nutrition Desk Reference. 3rd ed. New Canaan, Conn: Keats Publishing, Inc.; 1995:23-64.

Haas EM. Staying Healthy with Nutrition. Berkley, Calif: Celestial Arts Publishing; 1992:65-79.

Haw M, Linnebjerg H, Chavali SR, Forse RA. The effect of dietary polyunsaturated fatty acids (PUFA) on acute rejection and cardiac allograft blood flow in rats. Transplantation. 1995;60(6):570-577.

Jiang WG, Hiscox S, Bryce RP, Horrobin DF, Mansel RE. The effects of n-6 polyunsaturated fatty acids on the expression of nm-23 in human cancer cells. Br J Cancer. 1998;77(5):731-738.

Jiang WG, Hiscox S, Horrobin DF, Bryce RP, Mansel RE. Gamma linolenic acid regulates expression of maspin and the motility of cancer cells. Biochem Biophys Res Commun. 1997;237(3): 639-644.

Kruger MC, Coetzer H, DeWinter R, Gericke G, Papendorp DH. Calcium, gamma-linolenic acid and eicosapentaenoic acid supplementation in senile osteoporosis. Aging (Milano). 1998;10(5):385-394.

Murray MT. Encyclopedia of Nutritional Supplements. Rocklin, Calif: Prima Publishing; 1996:239-278.

Newstrom H. Nutrients Catalog. Jefferson, NC: McFarland & Co. Inc; 1993:103-105.

Shils ME, Olson JA, Shike M, Ross AC. Modern Nutrition in Health and Disease. 9th ed. Baltimore, Md: Williams & Wilkins; 1999:90-92, 1377-1378.

Wagner W, Nootbaar-Wagner U. Prophylactic treatment of migraine with gamma-linolenic and alpha-linolenic acids. Cephalalgia. 1997;17(2):127-130.

Werbach MR. Nutritional Influences on Illness. 2nd ed. Tarzana, Calif: Third Line Press; 1993:13-22, 655-671.

Ziegler EE, Filer LJ, eds. Present Knowledge in Nutrition. 7th ed. Washington, DC: ILSI Press; 1996:58-64.