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Report: Pregnant Women Should Avoid Canned Tuna

Recommendations published in the magazine Consumer Reports this week urge women to avoid eating any canned tuna while pregnant because of uncertainties about the risk of mercury contamination to developing fetuses.

The recommendations are stricter than the federal government’s advice issued two years ago. Then, the FDA advised women and young children to limit -- but not avoid -- consumption of canned tuna because of contamination.

But the magazine’s experts say women should avoid the popular item altogether because of FDA data showing that some canned tuna may have higher mercury levels than once thought.

“What we did is take a closer look at the data,” says Urvashi Rangan, PhD, a toxicologist and a senior scientist at Consumer Reports.

Concerned About Mercury in Fish?

Higher-Than-Average Levels

Canned tuna and most other fish and seafood contain some amount of toxic mercury that has worked its way through the food chain because of industrial pollution. In adequate doses the metal can damage the developing nervous system in fetuses and children.

The FDA specifically warns against the consumption of shark, swordfish, king mackerel, or tile fish -- which have high levels of mercury -- by women who are nursing, or women who are pregnant or of childbearing age; the FDA warning also applies to young children.

In 2004, the FDA urged women and young children to eat no more than 12 ounces of a variety of fish and shellfish with lower levels of mercury (including canned light tuna) or 6 ounces of white tuna (albacore) per week to minimize mercury risks. Canned light tuna on average contains lower mercury levels, the agency said.

But theConsumer Reports analysis of the FDA’s data shows that 6% of cans of light tuna contained at least as much mercury as white tuna, also known as albacore. It wasn’t enough to skew the average beyond white tuna, but enough to warrant concern for pregnant women, Rangan says.

“We’re not telling you not to eat tuna. But for pregnant women in particular where you are talking about potential fetal exposure -- and it’s an avoidable risk -- we’re saying go ahead and take some extra measures to reduce your Hg [mercury] exposure at all costs,” she tells WebMD.

What You Need to Know About Eating Fish

FDA Interpretation

David Acheson, MD, chief medical officer of FDA’s Center for Food Safety and Applied Nutrition, says the agency does not dispute the magazine’s calculations. Acheson says that “a single dose of mercury is not good.”

But he says that a years-long scientific review convinced the agency that there is little danger even if pregnant women eat canned light tuna with higher-than-average mercury contamination once in a while.

“We are not aware of any science that would indicate that having an occasional meal at that level would cause any harm, and if that science is out there, I would love to see it,” Acheson tells WebMD.

Consumer Reports urged women of childbearing age to limit tuna consumption to about three chunk-light cans per week or one can of white tuna (albacore) or solid-light tuna, since mercury can linger in the body even after you are no longer eating it.

Six-ounce servings of lower-mercury seafood -- including salmon, tilapia, shrimp, and clams -- appear safe for daily consumption by women, the magazine said; three-ounce servings for small children up to 45 pounds also appear safe.

Myths, Dos and Don’ts for a Healthy Pregnancy

Other Perspectives

Joshua T. Cohen, PhD, a lecturer at the Institute for Clinical Research at the Tufts New England Medical Center in Boston, says Consumer Reports was misinterpreting the significance of data showing that 6 percent of light-tuna cans exceed averages for higher-mercury white tuna.

“What your body sees is the average [mercury dose] over several weeks. The idea that the departure above the average on one day is going to mean a bad health outcome is like saying that two slices of apple pie at Thanksgiving is going to lead to obesity,” says Cohen, who authored a major study on the risks and benefits of fish consumption. The study was funded by food industry groups and the US Tuna Foundation, another industry group.

A statement by the foundation said tuna has proven health benefits and that Consumer Reports had done “a great disservice” by using “incomplete facts.”

Rangan says that more-than-usual caution is warranted for pregnant women.

“We’re talking about exercising caution for a particularly vulnerable population with fetuses with vulnerable nervous systems. The fact of the matter is that it’s a preventable risk, so why when there are so many options, wouldn’t you want to minimize your risk of exposure,” she says.

Pregnant? Follow WebMD's Fetal Development Timeline

By Todd Zwillich, reviewed by Louise Chang, MD

SOURCES: Mercury in Tuna: New Safety Concerns. Consumer Reports, July, 2006. Urvashi, Rangan, PhD, senior scientist, Consumer Reports. David Acheson, MD, chief medical officer, FDA Center for Food Safety and Applied Nutrition. US Tuna Foundation. Joshua T. Cohen, PhD, lecturer, Institute for Clinical Research and Health Policy Studies, Tufts New England Medical Center.