Fish oil supplements may contain flame retardants

Flame retardants have been showing up in some surprising places, from human breast milk to peregrine falcon eggs. Now this growing list can be expanded to include dietary supplements based on cod liver oil, according to a new study.

European scientists have found that flame retardant levels have increased significantly during the past four years in products containing cod liver oil, a common component of dietary supplements. The report appears in the April 7 edition of the Journal of Agricultural and Food Chemistry, a peer-reviewed journal of the American Chemical Society, the world’s largest scientific society.

Fish and vegetable oils are in high demand as dietary supplements because they contain omega 3 fatty acids, which have been linked to various health benefits, including reduced risk of heart disease.

In recent years, however, scientists have shown that fish oils are prone to contamination by organic chemicals. For example, researchers have found that farm-raised salmon contain more contaminants than wild salmon, which they attribute partly to the fish oils used to supplement salmon feed.

“We analyzed 21 commercially available fish and vegetable oil dietary supplements for selected contaminants,” says Miriam Jacobs, Ph.D., who lectures in food safety and toxicology at the University of Surrey in Guildford, U.K, and was one of the authors of the latest study involving cod liver oil. The supplements, purchased from retailers in the U.K., contained four classes of oils: pure vegetable oils, fish and vegetable oil formulations, cod liver oil and whole body fish oil.

Jacobs and her coworkers measured levels of persistent organic pollutants in the supplements, including pesticides, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), which are used widely as flame retardants. They then compared the values with levels measured in the same brands purchased eight years ago from the same retailers, and with fish oils used to supplement salmon aquaculture feeds obtained four years ago. In earlier work, Jacobs had found a relationship between pollutants in these feeds and in farmed European salmon.

Supplements based on vegetable oil and whole body fish oil showed little or no contamination throughout the current and previous studies. “The cod liver oils have similar levels of PCBs and pesticides compared to samples obtained from the same outlets,” Jacobs says. “But the levels of flame retardants are higher.”

Flame retardant levels in cod liver oils from the new study ranged from about 15-34 nanograms per gram of fat, while the range was 0-13 only four years ago. “This is a relatively large increase,” Jacobs says. “The extensive use of these chemicals in recent years means that they can get into places where they shouldn’t be, such as the marine environment.”

The findings add to a growing number of studies that have found flame retardants in unexpected places, from human breast milk in the United States to peregrine falcon eggs in Sweden.

Not only does the new study have environmental implications, but it could also have dietary repercussions. “It suggests that a consumer can reduce her or his intake of the persistent organic pollutants by changing to a formulation that contains less cod liver oil, and that contains a proportion of vegetable oil sources of omega 3 fatty acids,” Jacobs says.

Vegetable oils contain short-chain fatty acids, which are generally thought to offer less health benefit than the long-chain fatty acids from fish oils. Researchers have shown, however, that humans can metabolize and produce long-chain fatty acids from short-chain vegetable sources. This metabolism may not be very efficient, according to Jacobs, so a healthy adult would probably need to consume 8-10 times more vegetable oil supplements to get similar health benefits.

These are not definitive dietary recommendations, Jacobs cautions. “We hope these findings will stimulate further research into the newer pollutants to better protect the public and the environment,” she says. “Regulatory authorities conduct food-monitoring programs for dioxins and PCBs, but far less so for other contaminants.”

Regulations should also consider other potential routes of exposure, Jacobs says, including farmed salmon that are fortified with fish oil to increase their omega 3 fatty acid content. Fish oils are also used as feed supplements for farm animals, including sheep, cows and chickens.