Omega-3 Fatty Acids, Fish Oil, Alpha-Linolenic Acid : Safety

by MedlinePlus

(Page 5 of 6)

Allergies

People with allergy or hypersensitivity to fish should avoid fish oil or omega-3 fatty acid products derived from fish. Skin rash has been reported rarely. People with allergy or hypersensitivity to nuts should avoid alpha linolenic acid or omega-3 fatty acid products that are derived from the types of nuts to which they react.

Side Effects and Warnings

General: The U.S. Food and Drug Administration classifies intake of up to 3 grams per day of omega-3 fatty acids from fish as GRAS (Generally Regarded as Safe). Caution may be warranted, however, in diabetic patients due to potential (albeit unlikely) increases in blood sugar levels, patients at risk of bleeding, or in those with high levels of low-density lipoprotein (LDL). Fish meat may contain methylmercury and caution is warranted in young children and pregnant/breastfeeding women.

Bleeding: Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids ("Eskimo" amounts) may increase the risk of hemorrhagic (bleeding) stroke. High doses have also been associated with nosebleed and blood in the urine. Fish oils appear to decrease platelet aggregation and prolong bleeding time, increase fibrinolysis (breaking down of blood clots), and may reduce von Willebrand factor.

Environmental contamination: Potentially harmful contaminants such as dioxins, methylmercury, and polychlorinated biphenyls (PCBs) are found in some species of fish. Methylmercury accumulates in fish meat more than in fish oil, and fish oil supplements appear to contain almost no mercury. Therefore, safety concerns apply to eating fish but likely not to ingesting fish oil supplements. Heavy metals are most harmful in young children and pregnant/nursing women. For sport-caught fish, the U.S. Environmental Protection Agency recommends that intake be limited in pregnant/nursing women to a single 6-ounce meal per week, and in young children to less than 2 ounces per week. For farm-raised, imported, or marine fish, the U.S. Food and Drug Administration recommends that pregnant/nursing women and young children avoid eating types with higher levels of methylmercury (approximately 1 part per million, such as mackerel, shark, swordfish, or tilefish), and less than 12 ounces per week of other fish types. Women who might become pregnant are advised to eat 7 ounces or less per week of fish with higher levels of methylmercury (up to 1 part per million), or up to 14 ounces per week of fish types with approximately 0.5 parts per million (such as marlin, orange roughy, red snapper, or fresh tuna). Unrefined fish oil preparations may contain pesticides.

Gastrointestinal symptoms: Gastrointestinal upset is common with the use of fish oil supplements, occurring in up to 5 percent of patients in clinical trials, with nausea in up to 1.5 percent of patients. Diarrhea may also occur, with potentially severe diarrhea at very high doses. There are also reports of increased burping, acid reflux/heartburn/indigestion, abdominal bloating and abdominal pain. Fishy aftertaste is a common effect. Gastrointestinal side effects can be minimized if fish oils are taken with meals and if doses are started low and gradually increased.

Blood pressure effects: Multiple human trials report small reductions in blood pressure with intake of omega-3 fatty acids. Reductions of 2-5 mmHg have been observed, and effects appear to be dose-responsive (higher doses have greater effects). DHA may have greater effects than EPA. Caution is warranted in patients with low blood pressure or in those taking blood-pressure lowering medications.

Blood sugar levels/diabetes: Although slight increases in fasting blood glucose levels have been noted in patients with type 2 ("adult onset") diabetes, the available scientific evidence suggests that there are no significant long-term effects of fish oil in patients with diabetes, including no changes in hemoglobin A1clevels. Limited reports in the 1980s of increased insulin needs in diabetic patients taking long-term fish oils may be related to other dietary changes or weight gain.

Vitamin levels: Fish oil taken for many months may cause a deficiency of vitamin E, and therefore vitamin E is added to many commercial fish oil products. As a result, regular use of vitamin E-enriched products may lead to elevated levels of this fat-soluble vitamin. Fish liver oil contains the fat-soluble vitamins A and D, and therefore fish liver oil products (such as cod liver oil) may increase the risk of vitamin A or D toxicity.

Cholesterol levels: Increases (worsening) in low-density lipoprotein levels ("bad cholesterol") by 5-10% are observed with intake of omega-3 fatty acids. Effects are dose-dependent with effects likely to occur at 1 gram per day or greater of omega-3 fatty acids.

Liver (hepatic) effects: Mild elevations in liver function tests (alanine aminotransferase) have been reported rarely.

Dermatologic effects: Skin rashes have been reported rarely.

Neurologic/psychiatric effects: There are rare reports of mania in patients with bipolar disorder or major depression. Restlessness and formication (the sensation of ants crawling on the skin) have also been reported.

Calories: Fish oils contain approximately 9 calories per gram of oil.

Pregnancy and Breastfeeding

Potentially harmful contaminants such as dioxins, methylmercury, and polychlorinated biphenyls (PCBs) are found in some species of fish, and may be harmful in pregnant/nursing women. Methylmercury accumulates in fish meat more than in fish oil, and fish oil supplements appear to contain almost no mercury. Therefore, these safety concerns apply to eating fish but likely not to ingesting fish oil supplements. However, unrefined fish oil preparations may contain pesticides.

For sport-caught fish, the U.S. Environmental Protection Agency recommends that intake be limited in pregnant/nursing women to a single 6-ounce meal per week. For farm-raised, imported, or marine fish, the U.S. Food and Drug Administration recommends that pregnant/nursing women avoid eating types with higher levels of methylmercury (approximately 1 part per million, such as mackerel, shark, swordfish, or tilefish), and less than 12 ounces per week of other fish types.

Women who might become pregnant are advised to eat up to 7 ounces per week of fish with higher levels of methylmercury (up to 1 part per million), or up to 14 ounces per week of fish types with approximately 0.5 parts per million (such as marlin, orange roughy, red snapper, or fresh tuna).

It is not known if omega-3 fatty acid supplementation of women during pregnancy or breastfeeding is beneficial to infants. It has been suggested that high intake of omega-3 fatty acids during pregnancy, particularly DHA, may increase birth weight and gestational length. However, higher doses may not be advisable due to the potential risk of bleeding. Fatty acids are added to some infant formulas.

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