Fish is healthy. Fish is unhealthy. Oh wait, fish is healthy again. A new study has found that the abundant omega-3s found in fish oil may cancel out any negative effects of mercury exposure from fish consumption.

For generations, fish was praised as a healthy low-fat source of nutrients. But as early as the 1970s, health experts raised concerns about the levels of mercury contained in fish — mercury that came from both natural and human-made sources. The biggest worry about the levels of mercury noted in fish was that this exposure might harm the developing brains of unborn babies.

By 2000, the Food and Drug Administration (FDA) officially warned pregnant women that they should limit their fish consumption — and potential mercury exposure. The FDA's most recent guidelines suggest limiting fish to two to three servings per week. The agency also suggested that pregnant women choose fish that are lower in mercury, such as salmon, shrimp, pollack, tuna (light canned), tilapia, catfish and cod, while avoiding fish with higher mercury content — tilefish, shark, swordfish and king mackerel.

But a new study, published in the American Journal of Clinical Nutrition, has health experts taking a closer look at fish and mercury and questioning the notion that too much fish consumption might be unhealthy for developing babies. 

In the Seychelles, a chain of islands in the Indian Ocean, consumption of fish is the norm. Pregnant women generally eat at least 12 servings of fish per week. That's four times the amount recommended by the FDA. But three decades of research on the islands has not found any evidence of a link between mercury exposure and developmental disorders in newborn babies.

For the study, researchers tracked more than 1,500 mothers and their children from pregnancy until the children reached their late teens and 20s. At around 20 months after birth, the children were tested to measure their communication, behavior and motor skills. Mercury levels in the mothers were tested during pregnancy and after using hair samples. Researchers found that mercury exposure did not correlate with lower test scores. Some of the children are now in the 20s and still show no developmental delays due to mercury exposure in the womb.

Researchers think it is the omega-3s found in the fish that are counteracting the potential damage caused by the mercury.

"The fish oil is tripping up the mercury," said study co-author Edwin van Wijngaarden, an associate professor in the University of Rochester's department of Public Health Sciences in Rochester, N.Y. "Somehow, they are interacting with each other. We found benefits of omega 3s on language development and communications skills."

This new study comes just as the FDA and other international agencies have announced plans to revisit their policies on fish consumption during pregnancy. Will it affect the recommendations developed for the next generation of pregnant women and their babies? Should it? 

Related on MNN: