Q & A Library

Updated 7/12/2005

I'm afraid your concern is justified. Despite assurances from manufacturers, some fish oil supplements probably do contain toxins. My colleague Kathleen Johnson, a nutritionist here at the Program in Integrative Medicine, tells me that she's not sure if heavy metals as well as pesticides and PCBs are a problem. However, she notes that results from a study published in 1998 indicate that tests of 44 different fish oil supplement brands sold in 15 countries between 1994 and 1995 revealed appreciable quantities of organochlorines including PCBs and pesticide residues.

So far, the only reports of potential health consequences of contaminated fish oil supplements indicate that they may increase the risk of breast cancer, but this link isn't well established.

We all need the omega-3 fatty acids in fish oil for long-term health and to reduce our risks of heart disease, cancer, decrease inflammation and enhance mood. If you're healthy, you're better off getting omega-3s not by a fish oil supplement but by eating at least three servings per week of oily fish (wild Alaskan salmon, mackerel, sardines, herring). Avoid carnivorous fish such as swordfish and marlin, which spend a lot of time in coastal waters where pollution levels are highest; bluefish, which tend to concentrate mercury; and albacore tuna, which may harbor the same pollutants as swordfish and marlin.

However, some people may benefit from taking fish oil capsules in addition to eating fish. Ms. Johnson recommends them to those with autoimmune or inflammatory disorders, heart disease, diabetes, mental or emotional disorders, or insulin resistance. Because they can affect blood clotting, avoid fish oil supplements if you're taking any anticoagulant drugs like Coumadin (warfarin), have had a hemorrhagic stroke, or are scheduled for surgery.

While omega-3s are beneficial in almost any dose for these conditions, if you are not getting any omega-3's from your diet, you may have difficulty getting adequate levels of EPA (eicosapentaenoic acid) and DHA (docoahexaenoic acid) from fish oil capsules alone. Choose a brand that provides high levels of both EPA AND DHA in the least number of capsules and are distilled to remove PCBs and other contaminants.

Andrew Weil, M.D.