Flaxseed Oil

Overview

Flaxseed oil is a rich source of alpha-linolenic acid (ALA), an omega-3 fatty acid. Omega-3 fatty acids (n-3) constitute one of two major families of polyunsaturated fatty acids, the other family being omega-6 (n-6). ALA is the parent substance of the n-3 fatty acid family. Linoleic acid is the parent substance for the n-6 fatty acid family. These two families have very different biochemical roles in the body. ALA is an essential fatty acid and is necessary for the normal function of all tissues. Through a series of steps, it is metabolized to eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and prostaglandins in the body. Prostaglandins are hormone-like compounds that help regulate blood pressure, blood clotting, heart rate, vascular dilation, lipolysis, and immune response.

American diets are typically high in n-6 fatty acids and low in n-3 fatty acids. The average diet supplies only 0.15 g of n-3 fatty acids per day. A high ratio of n-6:n-3 fatty acid may encourage production of proinflammatory metabolites (arachidonic acid, prostaglandin E₁, and prostaglandin E₂) and negatively affect the body's response to disease. Changing the intake of dietary fatty acids may modify the body's response to disease, injury, and infection. Clinical trials indicate that supplementation with n-3 fatty acids from plants such as flaxseed can encourage production of the anti-inflammatory metabolites and inhibit the production of pro-inflammatory metabolites.

ALA is used as a source of energy by the body and partly as a precursor of the metabolites. Most studies indicate that a certain amount of ALA is converted to EPA in the body but conversion to DHA is limited. Results of one study showed that with a diet high in saturated fat conversion to EPA and DHA is approximately 6% and 3.8%, respectively. With a diet rich in n-6 polyunsaturated fatty acids, conversion is reduced by 40% to 50%. Flaxseed oil raises tissue EPA levels comparably to fish oil when dietary linoleic acid is restricted. In one study, the degree of conversion was proportional to a weekly portion (50 to 100 g) of fatty fish depending on the fat content of the fish. In some instances, ALA may be an effective alternative to fish oil supplements. However, a high ratio of ALA:linoleic acid may be necessary to produce the effects demonstrated after ingesting fish oils.

Deficiencies in essential fatty acid can reduce both primary and secondary immune responses and modify the inflammatory response in animals. Symptoms associated with a deficiency in n-3 fatty acids include neurological changes (parasthesias, weakness, pain in the legs, inability to walk) and impaired vision.

Dietary Sources

Ground flaxseed or flaxmeal

Constituents/Composition

Flaxseed contains 55% to 65% essential fatty acids, beta-carotene, and mixed carotenoids. Some processors add vitamin E to increase the oil's stability and shelf life.

Commercial Preparations

• Flaxseed oil is easily destroyed by heat, light, and oxygen.
• For optimal stability, seeds should be fresh pressed at low temperatures in the absence of light, extreme heat, or oxygen.
• Flaxseed oil is available in liquid and softgel capsule form, and should be refrigerated to prevent rancidity.
• Liquids require bottling in nonreactive, opaque or dark containers to prevent transmission of light. Capsules require similar packaging.
• Flaxseed oil can be used on salads and cooked vegetables or added to foods after they have been cooked. Flaxseed oil should not be heated since this destroys its anti-inflammatory qualities.

Therapeutic Uses

• Inflammation. Arachidonic acid and its proinflammatory metabolites are released from membrane phospholipids during an inflammatory reaction. EPA and DHA decrease the production of pro-inflammatory prostaglandins and thromboxanes from arachidonic acid. EPA competes with liberated arachidonic acid and induces the production of less inflammatory and chemotactic derivatives. A 1:1 or 1.3:1 ratio of ALA:linoleic acid may be optimal for reducing arachidonic acid production. This gives flaxseed oil a use in inflammatory conditions such as arthritis, asthma, allergies, and dysmenorrhea.
• Skin disorders. A small amount of research indicates that n-3 fatty acids may be of value in alleviating certain skin diseases such as psoriasis.
• Immune system. Studies in humans and animals have demonstrated that flaxseed oil is as effective as EPA at inhibiting the autoimmune reaction. This may prove useful in such conditions as rheumatoid arthritis and ulcerative colitis.
• Hypertension. Fish oil or flaxseed oil appear to be very effective in lowering blood pressure. One tablespoon of flaxseed oil per day can lower both the systolic and diastolic readings by up to 9 mm Hg.
• Cardiovascular disease. n-3 fatty acids have been shown to improve lipid profiles in hundreds of studies. The majority of studies used fish oils, not flaxseed oil. The few studies conducted with flaxseed oil indicate that it is not equivalent to fish oil. Large quantities of flaxseed oil are required to induce similar effects seen with fish oils. Flaxseed may offer some cardiovascular protection by improving arterial circulation and arterial function in high-risk subjects.
• Diabetes. Flaxseed oil may be a safer alternative to fish oil supplements in diabetics with altered lipid metabolism. High doses of fish oils have been shown to increase blood lipids and worsen blood sugar control in some individuals. However, some Type II diabetics may have low delta-6-desaturase activity, which prevents them from efficiently converting ALA to EPA in the body; flaxseed oil may not be an effective therapy in these individuals.
• Nephritis. Flaxseed oil reduced glomerular filtration injury and declining renal function in a rat-5/6 renal ablation model. Blood pressure, plasma lipids, and urinary prostaglandins were also favorably affected by the flaxseed oil treatment.
• Drug resistance. ALA, gamma-linolenic acid, EPA, and DHA have been shown to reverse tumor cell drug resistance in vitro.

Dosage Ranges and Duration of Administration

One to 3 tsp. liquid flaxseed oil per day, or 3,000 mg (capsules) bid, as a starting dose is most recommended.

Dosage for disease prevention and treatment will vary depending on fatty acid content of the diet, individual body physiology (ALA conversion to EPA), and the type of disorder.

Side Effects/Toxicology

There are no side effects or toxicity associated with increased intake of flaxseed oil.

Warnings/Contraindications/Precautions

Flaxseed oil can add additional calories and fat to the diet if there is not a compensatory reduction in other fats.

Interactions

No clinically significant interactions between flaxseed oil and conventional medications are known to have been reported in the literature to date, including the German Commission E monograph (Blumenthal 1998). Although clinical relevance is unknown, flaxseed oil may interfere with the absorption of certain medications; therefore, ingestion of flaxseed oil several hours before or after other herbs or medications may be warranted. Please see monograph on Alpha Linolenic Acid for additional information regarding that active ingredient.

References

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