The U.S. Food and Drug Administration has established doses of up to 3 grams per day of omega-3 fatty acids from fish as generally regarded as safe. If taken as directed, omega-3 fatty acid pills can contribute to reductions in blood pressure, improvements in high-density lipoproteins (HDL)--the good cholesterol--and reductions of triglycerides in the blood. They may also significantly reduce the occurrence of heart attack and sudden death from coronary heart disease. However, for some individuals and if taken in high doses, omega-3 fatty acids may produce unwanted and potentially harmful side effects.
Increased LDL Cholesterol Levels
If omega-3 pills are taken in high doses, low-density lipoprotein (LDL) levels (the "bad" cholesterol) may increase by a small amount. Consequently omega-3s may work against LDL-lowering statin drugs, such as atorvastatin (Lipitor) and lovastatin (Mevacor) or foods such as barley, garlic and soy.
Gastrointestinal Upset
Diarrhea, nausea, bloating, gas and belching are some common gastrointestinal effects that may arise if large amounts of omega-3 pills are taken. Reducing total dosage or building up to the daily recommended dose may alleviate these symptoms. A fishy aftertaste in the mouth is also common.
Bleeding
Omega-3 fatty acids inhibit the function of platelets, so in high doses, concern over bleeding arises. High doses of omega-3 pills are associated with nosebleeds and blood in the urine. They may decrease platelet aggregation, resulting in prolonged bleeding time, fibrinolysis (breaking down of blood clots), and reductions in von Willebrand factor (a protein that helps the blood clot). Very large amounts of omega-3s (referred to as "Eskimo amounts") may increase the risk of hemorrhagic stroke.
Heavy Metal Contamination
Pollutants such as dioxins, methylmercury, polychlorinated biphenyls (PCBs) may be found in certain oily fish. The FDA advises pregnant women, those who may become pregnant, those who are breast-feeding and young children to avoid eating these types of fish. The National Institutes of Health report that toxins like methylmercury seem to be present in fish more than fish oil, and high-quality omega-3 supplements are not likely to contain mercury.
Vitamin Toxicity
Omega-3 fish oils often contain vitamin A, D and E. If you consume large amounts, elevated and potentially toxic levels of these vitamins may be found in your blood. Vitamin A toxicity may be acute or chronic and results in headache, increased intracranial pressure, nausea and vomiting, according to the Merck Online Medical Library. Chronic cases also demonstrate changes in skin, hair and nails as well as liver abnormalities. High levels of vitamin E can result in increased risk of hemorrhagic stroke or death. Vitamin D toxicity causes hypercalcemia (excessive calcium in the blood), which then may lead to anorexia, vomiting, weakness, nervousness and eventually renal failure.
Blood Glucose Effects
There is some evidence that omega-3 fatty acids may increase blood glucose levels among individuals with type 2 diabetes. However, as reported by the NIH and The American Academy of Family Physicians, available research suggests there are no long-term effects of omega-3s on blood glucose, including hemoglobin A1c levels, among diabetics.
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