Mercury Rising?

Conflicting reports over contaminants in fish have left many pregnant women reeling. Here's the bottom line.


It's a conundrum: You know seafood is one of the healthiest foods you can eat. Rich in protein and other essential nutrients, swimming with heart-healthy omega-3 fatty acids and low in saturated fats, these watery wonders have likely been a part of your weekly—if not daily—diet for years. But now that you're pregnant, you're being pummeled with news that fish may not be so healthy after all. What gives?

Virtually all experts agree that seafood is an important part of every person's diet, even—and, some say, especially—during pregnancy. Others warn that eating too much seafood when pregnant can potentially lead to dangerous levels of methyl mercury (a toxin that collects in streams, oceans and, ultimately, fish) in the mother's body, raising the risk of neurological damage to her developing fetus. Confused? So were we. To help sort out the issue, we went to some of the foremost experts and researchers in the field. Here's the latest information on this vexing topic.

Warnings: more harm than good?

All seafood contains some amount of mercury. Citing concerns about the possibility of a link between this toxin and impaired language, memory, cognitive thinking and fine-motor and visual-spatial skills among children who were exposed to it in utero, the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) have established fish-intake guidelines for women who are pregnant or might become pregnant (and, later, when nursing). These agencies don't recommend avoiding seafood altogether, but they do suggest steering clear of varieties with the highest mercury content and limiting the consumption of all others. Here's a recap of their advisory:

• Avoid large, predatory fish such as shark, swordfish, king mackerel and tilefish. (As big fish eat smaller fish, the larger, longer-living ones accumulate more mercury.)

• Eat up to 12 ounces a week of a variety of fish and shellfish that are lower in mercury, such as shrimp, canned light tuna, salmon, pollock and catfish.

• Albacore tuna has more mercury than light tuna, so limit your intake to 6 ounces (one average meal) per week.

• Before eating any non-commercial seafood (such as that caught by family or friends), check with your local branch of the EPA or health department to make sure the water it was taken from is safe. If this information isn't available, eat up to 6 ounces per week of this fish, but don't eat any other seafood that week.

Good intentions aside, the problem with these guidelines, experts say, is that many women have become so confused and frightened that they are now eating too little seafood—or, in some cases, have stopped eating it altogether. "The mercury advisory, which was intended to be very selective, has really caused unintentional confusion," says Dariush Mozaffarian, M.D., DrPH, an assistant professor at Harvard Medical School and a cardiologist at Brigham and Women's Hospital, both in Boston.

"Although women aren't getting this message, the advisory recommends that only four species of fish be avoided entirely, that one species (albacore tuna) be limited to once a week and that all others be eaten," adds Mozaffarian, who is a co-author of a 2006 study on the benefits of seafood. "What's more, both the FDA advisory board and our study say that women and young children in particular should include fish in their diet."

Why is seafood so important during pregnancy? "The long-chain omega-3 fatty acids found in fish, especially DHA, are essential for brain development," says Gary J. Myers, M.D., a professor of neurology, pediatrics and environmental medicine at the University of Rochester Medical Center in Rochester, N.Y. "The body does not manufacture adequate amounts of these fatty acids, so they must be obtained from dietary sources. During pregnancy, a fetus can only get adequate amounts from its mother."

There are other potential benefits to consuming fish as well: "Some data show that eating sufficient amounts of seafood during pregnancy also helps prevent preterm birth and leads to developmental benefits and higher IQ," says Emily Oken, M.D., M.P.H., a primary care physician at the Fish Center for Women's Health at Brigham and Women's Hospital and an assistant professor at Harvard Medical School. "There also is some evidence of a lower risk of asthma and allergies later in life."

Rethinking the guidelines

The federal government's guidelines are designed to ensure that women avoid getting too much mercury, but recent studies show that the amount of seafood recommended may be too low to confer maximum benefits to babies. One such study, headed by Oken, looked at fish intake among more than 2,000 pregnant women.

"We did developmental testing on their children at ages 6 months and 3 years and found that the women who ate more than two servings of seafood per week—more than 12 ounces—had better outcomes related to IQ, as well as fine-motor, visual-motor and visual-spatial skills," says Oken.

Another study, reported in February 2007, found that among almost 12,000 pregnant women, those who had a seafood intake of less than 340 grams per week (equivalent to 12 ounces) had children who were more likely to be in the lowest range for verbal IQ scores. Low intake was also linked to poorer fine-motor, communication and social-development skills in the children, who ranged in age from 6 months to 8 years. "For each outcome measure, the lower the intake of seafood during pregnancy, the higher the risk of suboptimum developmental outcome," the study reported.

And certain types of seafood are more beneficial than others. "If a woman is eating 12 ounces per week of the oilier, darker, fattier fish, she's probably getting enough DHA," Mozaffarian says. "But if she's eating the same amount of white fish, she's probably not."

Alternatives to fish

Whether it's because they fear mercury or simply don't like seafood, some pregnant women wonder whether fish oil supplements can take the place of fish. Experts seem divided on the issue. Mozaffarian, for instance, says fish oil capsules "certainly have DHA" and are a reasonable alternative.

Myers prefers that women get their DHA from food sources. "Seafood contains more than just long-chain fatty acids," he explains. "It has high-quality protein and many other important nutrients that you might or might not get by simply taking a supplement." (Myers also points out that some other foods—walnuts, flax seed, enhanced eggs and grapeseed oil, for example—contain omega-3s.)

If you're concerned that fish oil supplements might contain mercury, be aware that a 2004 test conducted by showed that none of the 42 brands tested were contaminated with the toxin. (Fish oil supplements are not studied by the FDA.) What's more, a study published in the February 2007 issue of the European Journal of Clinical Nutrition found that among pregnant women with previous pregnancy complications—including preterm delivery, pregnancy-induced hypertension or intrauterine growth retardation—fish oil supplementation delayed the onset of delivery in the women with low or medium fish intake.

And if you're interested in the recent influx of foods with added omega-3s, be certain to read labels. "If you're going to rely on these foods to supply omega-3s, make sure they have DHA or EPA—or, even better, the combination," Mozaffarian advises. (ALA, another common omega-3, is not as beneficial for fetal development.) Daily Values have not been established for omega-3s and therefore may not be listed on a food's nutrition information label. Instead, most foods containing added omega-3s tout this elsewhere on the product packaging.

So what does all this information boil down to? Experts recommend the following:

• Follow the government's guidelines on the four types of fish to avoid entirely during pregnancy.

• Focus on smaller, darker, fattier types, which tend to have the highest amounts of omega-3s.

• To provide optimal benefits for your baby, consider eating more than the recommended 12 ounces per week. "The vast majority of seafood has almost undetectable amounts of mercury," says Mozaffarian, "so you can eat at least two servings a week of a variety of species and have no concern about contamination." However, he also recommends that people who consume five or more servings per week focus on varieties with the lowest mercury levels. (See "The Perfect 10?".)

Also keep in mind these words from Mozaffarian: "The key message is that there is some evidence of subtle danger to babies and infants from too much mercury, but there's even more consistent evidence of at least as much neurological danger from their mothers eating too little seafood."

What about PCBs?

Fish, meat and dairy foods all contain polychlorinated biphenyls (PCBs), a man-made mixture of chlorinated compounds often used in the manufacture of plastics and for other commercial uses before 1977.

Although manufacturing of PCBs was banned in the U.S. that year because of evidence of harmful health effects, these fat-soluble compounds build up in the environment, are stored in the tissues of animals and humans and take many years to break down. Overexposure in women can lead to having a baby with low birth weight, as well as problems with motor skills, short-term memory and the immune system.

However, dietary overexposure is not usually a concern for the general population, says Harvard's Dariush Mozaffarian, M.D., DrPH, who has conducted research on the benefits of seafood. "PCB levels in commercially available ocean-caught fish are far lower than FDA-action levels and should have little impact on individual decisions regarding fish consumption," he says. (Since levels in freshwater fish can vary depending on local conditions, consult your area's advisories before eating fish from these waters.)

Other experts feel that PCB levels can be an issue, especially when it comes to farmed fish; research is ongoing to determine the appropriate level of concern.

The Perfect 10?

The most recent research shows that eating more than the recommended 12 ounces of seafood a week may confer greater benefits to babies. If you choose to eat this much, stick with the following 10 varieties (listed here in alphabetical order); they are high in omega-3s and low in mercury: 1. Anchovies 2. Atlantic herring 3. Atlantic mackerel (not king mackerel) 4. Mussels 5. Oysters 6. Salmon 7. Sardines 8. Scallops 9. Shrimp 10. Trout