As research on the potential health benefits of fish oil accumulates, fish oil supplement sales have skyrocketed. The varied benefits of fish oil are credited to two compounds that are classified as omega-3 fatty acids: eicosa-pentaenoic (EPA) and deosahexaenoic acid (DHA). But with an abundance of choices on the market, how do you identify a superior fish oil supplement that contains potent amounts of these two substances without potential contaminants? Here’s what you need to know.

One of the common concerns with fish oil supplements relates to the product contamination, in particular the presence of polychlorinated biphenyls (PCBs), dioxins and heavy metals such as mercury. However, a recent report on fish oil supplements by Consumerlab.com found no detectable levels of mercury (less than 1.5 parts per billion) in the products analyzed. Consumer Reports also recently tested several popular brands and found that none contained significant levels of mercury, dioxins or PCBs.

The lack of mercury in fish oil supplements may be attributed to the fact that most mercury in fish is concentrated in the meat, not the oil. This is especially good news for those taking high therapeutic doses to treat neurological disorders such as bipolar disorder, schizophrenia and depression. Distillation processes used by most manufacturers to remove contaminants may also explain the lack of heavy metals and other toxins.

Many companies claim their fish oil is "pharmaceutical grade," creating the impression of superior quality and purity. However, there is not standard definition of pharmaceutical grade fish oil. Some companies base this claim on the concentrated potency of EPA and DHA in their products, while others emphasize a lack of impurities and contaminants.

Is there a difference in quality and efficacy between fish oil supplements found at grocery and drug stores compared with the more expensive ones available at health food stores?

Amounts and ratios of EPA and DHA vary significantly in supplements, but pricier fish oil supplements often have considerably higher potencies of EPA and DHA per capsule. High-quality fish oil supplements found at health food stores are typically more concentrated in omega-3s, often supplying more than twice the typical dose of both EPA and DHA. The best way to determine the quantity of omega-3s is to add the amounts of EPA and DHA provided per serving. For example "1,000 mg fish oil" supplement containing 180 mg of EPA and 120 mg of DHA provides 300 mg of omega-3 fatty acids.

One way to assess product purity and label accuracy of any supplement is to contact the company directly and request documentation of product verification by a third-party laboratory. Responsible companies that have done their homework and received good results will be more than happy to provide the information.