Much of the fish you eat is contaminated with mercury, a toxic element that finds its way from factories and power plants into rivers, lakes, and oceans. This has become a major public health issue in the U.S., but one that's as murky as the depths from which fisherman raise their catch.
Studies have shown that eating plenty of fish is healthy for pregnant women and their babies. But mercury can harm the developing brain of a baby whose mother eats too much contaminated fish, possibly causing learning disabilities and other neurological problems. Scientists know that for a fact. What's not clear, however, is exactly how much mercury is dangerous, and which fish pregnant women should be warned about.
Last year, the FDA put out an advisory to pregnant women, telling them not to eat shark, swordfish, king mackerel, and tilefish because samples of these fish had shown dangerously high levels of mercury contamination.
But instead of thanking the FDA for the kind advice, environmental activists and consumer watchdogs filleted the agency for failing to mention tuna -- arguably the most popular seafood in the U.S. Tuna has mercury in it. It doesn't have as much as the four fish mentioned in the advisory, but it has enough to raise concerns for many about how much a pregnant woman should eat.
Profits Over Public Health?
In February of this year, the Environmental Working Group (EWG), a research organization in Washington, went public with information that seems to finger the FDA in shady dealings regarding tuna's safety.
The FDA used focus groups to decide how to phrase the message about mercury in fish. One document shown to women in the focus groups mentioned limiting the amount of tuna they should eat during pregnancy. The limit was set at 12 oz. a week of canned tuna, or 3 oz. of tuna steak a week.
But FDA documents show that before drafting the final version of the advisory, agency officials met with tuna industry executives, who allegedly urged the agency to drop tuna from the advisory.
In response to the EWG's accusations, an FDA committee will meet this spring to review the advisory and the process that led up to it. But that's not to say they're admitting to any lapse in judgment. "FDA does stand behind the process," an agency spokesman says. "But we do understand the confusion that has arisen."
Going on what was learned in the focus groups, the FDA argues, most women would avoid tuna altogether if they were told to limit how much they eat. That means they would miss out on the health benefits of tuna, and the $6-billion-a-year tuna industry might suffer unnecessary losses. The EWG doesn't buy that explanation, saying that transcripts of the focus group sessions tell a different story -- that women were eager for information and ready to follow guidelines set down on paper. That's a matter of interpretation, but EWG spokeswoman Laura Chapin says, "The problem is using focus groups to determine if you should communicate" certain safety information. Instead, she says, the purpose should have been to find the best way to tell women what they have a right to know.
A Rock and a Hard Place
Knowing that it's risky to eat too much contaminated fish doesn't help women out of the quandary they're in, however. Just as mercury from fish can damage a baby's developing nervous system, some evidence shows that not eating enough fish may be harmful, too. Danish researchers reported in a February issue of the British Medical Journal that women who ate too little fish had a higher risk for premature delivery than women who ate a lot of fish did. The women who ate less fish also had a higher risk for having babies with low birth weight.
"Fish is an excellent source of nutrition, especially for pregnant women," says Daniel Lasser, MD, director of obstetric services at the Weill Cornell School of Medicine in New York. Some fish (like Pacific salmon, farmed catfish, and farmed trout) are nutritious and have very little mercury, but Lasser says he thinks tuna is particularly important because it's so popular and readily available. "I'm often asked about tuna," he says.
Chapin says the FDA may be underestimating how much tuna women eat: It's low in saturated fat; it's high in protein and omega-3 fatty acids; and it's cheap. "It's kind of a lifestyle-choice food," she says.
Lasser says he thinks public health advisories can go a long way toward preventing problems in the womb. For example, the push to get women to take folic acid supplements during pregnancy has led to a drop in cases of spina bifida (a spinal birth defect) in the U.S. But he says that trying to prevent exposure to toxins from otherwise healthy food is far more complicated.
How Much Is Too Much?
The FDA's safety limit for mercury in fish is 1 part per million (ppm). Samples of shark, king mackerel, swordfish, and tilefish that the FDA tested all had an average of about 1 ppm. Tuna steaks had an average of 0.32 ppm, and canned tuna had only 0.17 ppm.
But the EWG claims that FDA limits are too lax, and that many women eat enough tuna and other fish to raise the amount of mercury in their bodies to dangerous levels. They point to a study from the CDC showing that 10% of American women are very close to having enough mercury in their bodies to put their babies at risk, were they to get pregnant.
The Environmental Protection Agency's method for setting limits on mercury levels is different from the FDA's. The EPA limit, which is also endorsed by the National Academy of Sciences, allows up to 0.1 micrograms per kilogram of a person's body weight per day. The EWG claims that's eight times more protective than the FDA's limit.
But Lasser says he thinks none of the data the government agencies are going on is completely sound. "There's a great deal of uncertainty and lack of knowledge" about how much mercury is safe to eat, he says. "We don't know the half of it."
He says he warns his patients about the risks of eating fish, but he also tells them about the benefits. Lacking precise scientific data on how much is too much, he says, "How crazy you're going to get about it becomes a matter of personal choice."