A: Not as much as if you're eating the fish. Mercury is generally found in the fatty meat of the fish, not the oil. So while mercury levels in fish often range from 10 parts per billion (ppb) to 1,000 ppb, depending on the fish, the oil is often free of mercury and other contaminants.
In addition, some fish oils are made using species that are lower on the food chain, which are less likely to accumulate mercury. Nordic Naturals fish oil products, for example, use anchovies and sardines found off the coasts of Norway, Chile or Peru. And many companies, including Nordic Naturals, use a distillation process to further remove contaminants.
When the product testing company ConsumerLab.com looked at 41 omega-3 fatty acid supplement products, it found that none contained detectable levels of mercury (more than 10 ppb). Moreover, the products were fresh and contained their claimed amounts of the fatty acids, a surprise since supplements are not regulated like prescription drugs by the Food and Drug Administration and often fall short of their labeling claims.
Consumers should look for an oil that has less than 100 ppb for lead and mercury. Since this info isn’t on the label, check the International Fish Oil Standards (IFOS) Web sitenutrasource.ca/ifos, nutrasource% .ca/ifos_new, which lists all "Third Party Test Results" for products. You can also call the manufacturer or check the company Web site for these results.
Despite the contamination issues, eating fatty fish is still the best way to get omega-3s; just remember that long-lived, larger fish—shark, swordfish, king mackerel and tilefish—contain 1,000 ppb of mercury and shouldn't be eaten on a regular basis. (Pregnant women should avoid these fish altogether.)
If you do eat fish, it might help to sip green or black tea with your meal. Purdue University researchers have found that catechins in tea might reduce mercury absorption.