Oil from fish contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); both are omega-3 fatty acids.
Where is it found?
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.
Fish oil has been used in
connection with the following conditions (refer to the individual
health concern for complete information):
and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
Who is likely to be deficient?
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
convert to EPA.
At least four studies have reported a reduced blood level of omega-3 fatty acids in people
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.5
How much is usually taken?
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
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 has also
been reported to not cause the gastrointestinal symptoms that often result from taking regular
fish oil supplements, again suggesting unique benefit.6
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.7
However, in people who do not have cancer, the
maximum tolerated amount may be different.
Are there any side effects or interactions?
While those with heart disease and diabetes have often been reported to benefit from
supplementation with fish oil,89 both groups should check with their
doctor before taking more than 3 grams of fish oil per day for several months. Elevations in
blood sugar and cholesterol levels may occur
in some people who take fish oil.10
The increase in blood sugar appears to be related in part to the amount of fish oil
used.11 Some evidence suggests that adding vitamin E to fish oil may prevent the fish oil-induced
increase in blood sugar levels.12 In other research, the impairment of sugar
metabolism sometimes caused by supplementation with fish oil has been prevented by the
addition of half an hour of moderate exercise three times a week.13
While supplementation with fish oil consistently lowers triglycerides, the effect of fish oil on LDL
(“bad”) cholesterol varies, and in some people, fish oil supplementation has been
reported to increase LDL levels.14 People who took fish oil and who also took 15
grams of pectin per day were reported to have reductions in LDL cholesterol.15 This suggests that pectin
may overcome the occasional problem of increased LDL cholesterol reported in people who
supplement with fish oil. The LDL-cholesterol raising effect of EPA and DHA has also been reported to be prevented by taking
garlic supplements (or presumably including
garlic in the diet) along with EPA and DHA.16
Are there any drug
Certain medicines may interact with Fish Oil and Cod Liver Oil. Refer to drug interactions for a list of those medicines.
References (To view, roll mouse over the "References" heading; to hide, click on the heading)
1. Maes M, Smith R, Christophe A, et al. Fatty acid composition in major
depression: decreased omega 3 fractions in cholesteryl esters and increased C20: 4 omega
6/C20:5 omega 3 ratio in cholesteryl esters and phospholipids. J Affect Disord
2. Edwards R, Peet M, Shay J, Horrobin D. Omega-3 polyunsaturated fatty
acid levels in the diet and in red blood cell membranes of depressed patients. J Affect
3. Peet M, Murphy B, Shay J, Horrobin D. Depletion of omega-3 fatty acid
levels in red blood cell membranes of depressive patients. Biol Psychiatry
4. Maes M, Christophe A, Delanghe J, et al. Lowered omega 3
polyunsaturated fatty acids in serum phospholipids and cholesteryl esters of depressed
patients. Psychiatry Res 1999;85:275–91.
5. Navarro E, Esteve M, Olivé A, et al. Abnormal fatty acid pattern
in rheumatoid arthritis. A rationale for treatment with marine and botanical lipids. J
6. Belluzzi A, Brignola C, Campieri M, et al. Effects of new fish oil
derivative on fatty acid phospholipid-membrane pattern in a group of Crohn’s disease
patients. Dig Dis Sci 1994;39:2589–94.
7. Burns CP, Halabi S, Clamon GH, et al. Phase I clinical study of fish
oil fatty acid capsules for patients with cancer cachexia: cancer and leukemia group B study
9473. Clin Cancer Res 1999;5:3942–7.
8. Leaf A, Weber PC. Cardiovascular effects of n-3 fatty acids. N
Engl J Med 1988;318:549–57.
9. Malasanos TH, Stacpoole PW. Biological effects of omega-3 fatty acids
in diabetes mellitus. Diabetes Care 1991;14:1160–79.
10. Schectman G, Kaul S, Kassebah AH. Effect of fish oil concentrate on
lipoprotein composition in NIDDM. Diabetes 1988; 37:1567–73.
11. Toft I, Bonaa KH, Ingebretsen OC, et al. Effects of n-3
polyunsaturated fatty acids on glucose homeostasis and blood pressure in essential
hypertension. Ann Intern Med 1995;123:911–8.
12. Luostarinen R, Wallin R, Wibell L, et al. Vitamin E supplementation
counteracts the fish oil-induced increase of blood glucose in humans. Nutr Res 1995;
13. Dunstan DW, Burke V, Mori TA, et al. The independent and combined
effects of aerobic exercise and dietary fish intake on serum lipids and glycemic control in
NIDDM. Diabetes Care 1997; 20:913–21.
14. Harris WS, Zucker ML, Dujovne CA. Omega-3 fatty acids in type IV
hyperlipidemia: fish oils vs methyl esters. Am J Clin Nutr 1987;45:858 [abstr].
15. Sheehan JP, Wei IW, Ulchaker M, Tserng KY. Effect of high fiber
intake in fish oil-treated patients with non-insulin-dependent diabetes mellitus Am J Clin
Nutr 1997; 66:1183–7.
16. Adler AJ, Holub BJ. Effect of garlic and fish-oil supplementation on
serum lipid and lipoprotein concentrations in hypercholesterolemic men. Am J Clin
Nutr 1997; 65:445–50.
The information presented in Aisle7 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. 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