Fish Oil Purity: Mercury, PCBs, Dioxins and Third-Party Testing Programs

How refining works

Short-path distillation is established as the most effective industrial process to remove persistent organic pollutants from fish oil. [2] In one study, a 76% reduction of dioxin and PCB toxic equivalents in the starting oil was needed to meet the voluntary industry monograph; heating can cost some vitamins, but no adverse effect on nutritional quality was documented. [2] Results for refined oil should not be applied to whole fish.

What studies of finished supplements found

Units differ between studies (ng/g, pg TEQ/g, ng/kg), so numbers below are not directly comparable.

The UK survey is more than 20 years old and the EU limit applied afterwards, so it describes the past. [6] In Canada, the authors estimated that some salmon, tuna, herring and seal oils could contribute to exceeding a tolerable daily intake at recommended doses, and said it seemed prudent to choose oils from small, cold-water fatty fish; further research was needed. [7] In Japan, one shark liver oil product reached 58% to 70% of the Japanese tolerable daily intake, while most other products were under 5%. [8] In Spain, vegetable-oil supplements were clearly lower than fish-oil supplements. [9]

Industry standards and testing programs

GOED, an omega-3 industry trade association, publishes a voluntary monograph that focuses on oxidative quality, environmental contaminants and measurement of EPA and DHA, and requires its members to meet it. [10] GOED also says its randomized testing found members' products consistently passed; that statement comes from the trade body itself. [10] Independent third-party programs also exist. We describe them in general on Quality testing and certifications and name none here. A seal says a product was tested to that program's rules at some time, not that it suits you. The FDA states that it does not approve dietary supplements for safety and effectiveness. [11]

Cod liver oil

Fish liver oils also contain vitamins A and D in amounts that vary by product, and both can be harmful in excess. [12] The UK NHS advises people who are pregnant to avoid supplements containing vitamin A, including fish liver oil supplements such as cod liver oil. [13] See Cod liver oil.

Who should be extra careful

Pregnant or breastfeeding people, children, and anyone with liver or kidney conditions should ask a clinician before using fish oil; this page does not set amounts. For other contamination concerns see Product quality and contamination, and for fish itself see Farmed vs wild fish. Fish oil can affect bleeding; see Omega-3 safety and interactions.