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Fish Oil

What is fish oil? Why do we need it?

Fish oil is derived from fatty types of fish such as salmon and mackerel. The two main components of fish oil are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), a pair of omega-3 fatty acids. Both help lower levels of blood triglycerides and may stop the progression of atherosclerosis.

EPA and DHA are associated with numerous other health benefits as well. They can help treat inflammatory conditions such as Crohn's disease and rheumatoid arthritis; are vital in the creation of prostaglandins (which help dilate blood vessels); and may be useful in the treatment of schizophrenia. EPA and DHA also improve the functioning of the immune system. Animal studies have shown that fish oil can prevent some types of cancer in animals, but these results have not been duplicated in humans.

How much fish oil should I take?

Healthy people who frequently eat fatty fish usually do not need to take fish oil supplements. Most researchers who have studied EPA and DHA have used dosages equivalent to 10 grams of fish oil per day. Some positive effects have been in studies that used larger amounts (up to 21 grams per day).

What forms of fish oil are available?

Fish oil comes from oil fish such as mackerel, salmon, herring, sardines, cod, anchovies, and albacore tuna. The largest amounts of EPA and DHA are found in cod liver oil. The typical fish oil supplement contains 18 percent EPA and 12 percent DHA; more purified supplements contain higher amounts of DHA and EPA. Fish oil is available as a capsule, pill or extract.

What can happen if I take too much fish oil? Are there any interactions I should be aware of? What precautions should I take?

Taking more than 3 grams of fish oil per day for several months may increase blood sugar and cholesterol levels. As a result, patients with heart disease and diabetes should consult with a health care provider before taking fish oil supplements. Some research suggests that the increase in blood sugar levels may be ameliorated by taking vitamin E.

Fish oil may also interact with certain medications, including cyclosporine, pravastatin and simvastatin. As always, make sure to consult with a licensed health care practitioner before taking fish oil or any other dietary supplement or herbal remedy.


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  • Fenton WS, Dickerson F, Boronow J, et al. A placebo-controlled trial of omega-3 fatty acid (ethyl eicosapentaenoic acid) supplementation for residual symptoms and cognitive impairment in schizophrenia. Am J Psychiatry 2001;158:2071-4.
  • Gonzalez MJ. Fish oil, lipid peroxidation and mammary tumor growth. J Am Coll Nutr 1995;14:325.
  • Navarro E, Esteve M, Olive A, et al. Abnormal fatty acid pattern in rheumatoid arthritis. A rationale for treatment with marine and botanical lipids. J Rheumatol 2000;27:298-303.
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