BackgroundDietary sources of omega-3 fatty acids include fish oil and certain plant and nut oils. Fish oil contains both docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), while some nuts (such as English walnuts) and vegetable oils (such as canola, soybean, flaxseed, linseed, and olive oils) contain alpha-linolenic acid (ALA). There is supportive evidence from multiple studies that suggests the intake of recommended amounts of DHA and EPA in the form of dietary fish or fish oil supplements lowers triglycerides; reduces the risk of death, heart attack, dangerous abnormal heart rhythms, and strokes in people with known cardiovascular disease; slows the buildup of atherosclerotic plaques (“hardening of the arteries”), and lowers blood pressure slightly. However, high doses may have harmful effects, such as an increased risk of bleeding. Although similar benefits have been proposed for alpha-linolenic acid, the scientific evidence is less compelling, and the beneficial effects may be less pronounced. Some species of fish carry a higher risk of environmental contamination, such as with methylmercury. Dosing NB! The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy. Adults (18 years and older): Average Americans consume approximately 1.6 grams of omega-3 fatty acids daily, of which about 1.4 grams (~90%) comes from alpha-linolenic acid, and only 0.1-0.2 grams (~10%) comes from EPA and DHA. In Western diets, people consume roughly 10 times more omega-6 fatty acids than omega-3 fatty acids. These large amounts of omega-6 fatty acids come from the common use of vegetable oils containing linoleic acid (for example, corn oil, evening primrose oil, pumpkin oil, safflower oil, sesame oil, soybean oil, sunflower oil, walnut oil, and wheat germ oil). Because omega-6 and omega-3 fatty acids compete with each other to be converted to active metabolites in the body, benefits can be reached either by decreasing intake of omega-6 fatty acids or by increasing omega-3 fatty acids. For healthy adults with no history of heart disease, the American Heart Association recommends eating fish at least two times per week. In particular, fatty fish are recommended, such as anchovies, bluefish, carp, catfish, halibut, herring, lake trout, mackerel, pompano, salmon, striped sea bass, tuna (albacore), and whitefish. It is also recommended consuming plant-derived sources of alpha-linolenic acid, such as tofu, soybeans, walnuts, flaxseed oil, and canola oil. The World Health Organization and governmental health agencies of several countries recommend consuming 0.3-0.5 grams of EPA plus DHA and 0.8-1.1 grams of alpha-linolenic acid daily. A doctor and pharmacist should be consulted for dosing for other conditions. Children (younger than 18 years): Omega-3 fatty acids are used in some infant formulas, although effective doses have not been clearly established. Ingestion of fresh fish should be limited in young children, due to the presence of potentially harmful environmental contaminants. Fish oil capsules should not be used in children except under the direction of a physician. Safety NB! There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects. Allergies People with a known 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 a known 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
The U.S. Food and Drug Administration (FDA) classifies intake of up to three grams of omega-3 fatty acids from fish daily as GRAS (generally regarded as safe).
- Fish oil supplements may cause nausea, diarrhea, loose stools, decreased appetite, constipation, vomiting, and fat in the stools. Gastrointestinal side effects may be minimized if fish oils are taken with meals and if doses are started low and gradually increased.
- Mild elevations in liver function tests (alanine aminotransferase) have been reported rarely.
- 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.
- Other potential side effects include loss of short-term memory, headache, hemolytic anemia (abnormal breakdown of red blood cels), depression, somatic disorders (physical symptoms associated with psychological symptoms), increased risk of colon cancer, nasopharyngitis (inflammation in nose and throat), worsening of asthma symptoms, decreased physical activity, increased appetite, increased blood pressure, and an uncomfortable feeling.
- Fish meat may contain potentially harmful contaminants, such as dioxins, methylmercury, and polychlorinated biphenyls (PCBs). Caution is warranted in young children and pregnant or breastfeeding women.
- Omega-3 fatty acids may increase blood sugar levels. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
- Omega-3 fatty acids may increase low-density lipoprotein (LDL, or “bad”) cholesterol levels. Caution is advised in patients with high levels of LDL cholesterol.
- Omega-3 fatty acids may worsen symptoms for patients with ventricular tachycardia (rapid heartbeat). Use cautiously in patients with ventricular tachycardia (rapid heartbeat) or ventricular arrhythmia (abnormal heart rhythm).
- Omega-3 fatty acids may increase the risk of bleeding. Caution is advised in patients with bleeding disorders or those taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
- Omega-3 fatty acids may decrease blood pressure. Caution is warranted in patients with low blood pressure or in those taking blood pressure-lowering medications.
- Fish oil taken for many months may cause a deficiency of vitamin E and may increase the risk of vitamin A or D toxicity. Use large amounts cautiously.
- Use cautiously in individuals at risk for hormone imbalance or those undergoing hormone replacement therapy, as decreased estrogen receptor production has been associated with fish oil supplementation.
- Use cautiously in patients with asthma, inflammatory bowel disease, or liver disease, and in patients at risk for colon cancer, based on potential adverse effects associated with fish oil use.
- Avoid in individuals with a known hypersensitivity or allergy to fish oil or omega-3 fatty acid products derived from fish. Skin rashes have been reported rarely. Individuals with a known 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.
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 or 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.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 birthweight 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. The U.S. Environmental Protection Agency (EPA) recommends that fish intake be limited in pregnant and nursing women to a single six-ounce meal per week, and in young children to less than two ounces per week. Women who might become pregnant are advised to eat seven ounces of fish with higher levels of methylmercury or less per week, or up to 14 ounces per week of fish types with about 0.5 parts per million (such as marlin, orange roughy, red snapper, or fresh tuna).