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Presumably, healthy people who frequently eat fatty fish (several times per week) have no need to supplement with fish oil. How much EPA and DHA, if any, should be supplemented by healthy people who do not eat much fatty fish, remains unclear.
Most researchers studying the effects of EPA and DHA in humans who have a variety of health conditions have given those people at least 3 grams of the total of EPA plus DHA—an amount that may require 10 grams of fish oil, because most fish oil contains only 18% EPA and 12% DHA.
The health benefits for people with Crohn’s disease have been reported with a special, enteric-coated preparation of purified EPA/DHA manufactured from fish oil. This preparation of purified fatty acids does not cause the gastrointestinal symptoms that often result from taking regular fish oil supplements, which makes it a peferable source of EPA/DHA for people with gastrointestinal illnesses.200
In one trial, the maximum amount of fish oil tolerated by people being treated for cancer-related weight loss was reported to be approximately 21 grams per day.201 However, in people who do not have cancer, the maximum tolerated amount may be different.
EPA and DHA are found in mackerel, salmon, herring, sardines, sablefish (black cod), anchovies, albacore tuna, and wild game. Cod liver oil contains large amounts of EPA and DHA. Fish oil supplements typically contain 18% EPA and 12% DHA, though more purified (i.e., higher in EPA and DHA) fish oil supplements are sometimes available. In addition, DHA is available in a supplement that does not contain significant amounts of EPA.
So-called “primitive” diets have much higher levels of EPA and DHA than modern diets. As a result, some researchers and doctors believe that most people who eat a typical western diet are likely to be consuming less-than-optimal amounts of EPA and DHA. To a very limited extent, omega-3 fatty acids from vegetable sources, such as flaxseed oil, can be converted in the body to EPA.
At least four studies have reported a reduced blood level of omega-3 fatty acids in people with depression.202, 203, 204, 205
People with rheumatoid arthritis have been found to have decreased levels of omega-3 fatty acids, such as are found in fish oil, in their joint fluid and blood.206
Fish oil supplements typically contain 18% EPA and 12% DHA, though more purified (i.e., higher in EPA and DHA) fish oil supplements are sometimes available. Cod liver oil typically contains less EPA and DHA—roughly one-third to one-half less—than fish oil. Unlike fish oil, cod liver oil contains significant amounts of vitamins A and D. As for other sources of EPA and DHA, there are preparations that contain DHA without significant amounts of EPA, such as algae-based oils. In addition, Antarctic krill oil contains roughly 17% EPA and 10% DHA by weight.207
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The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2017.