Pregnant with her first child and worried about mercury, St. Petersburg resident Elizabeth Martin decided to play it safe. She bade farewell to her beloved shrimp and crab and stopped eating seafood altogether. ¶ Other than the occasional tantrum, 3-year-old Hannah Martin has turned out just fine. ¶ But her mother's extreme caution illustrates the quandary that has bedeviled government nutrition experts for years: ¶ The health benefits of eating some seafood may outweigh the risks of mercury.
Most seafood is full of omega-3 fatty acids that may add IQ points to a developing child's brain. In patients with cardiac troubles, it can stave off heart attacks.
But the word mercury can quickly turn people to beef, chicken and pork.
Now, the U.S. Food and Drug Administration is reassessing its dietary advice to consumers, looking more closely at the upside of seafood.
"Our focus has been on mercury. That's part of the problem,'' says Michael Bolger, a toxicologist who leads the FDA's advisory team. When the current advice was drafted in 2004, "we simply didn't have enough time to look at the huge benefits of fish consumption.''
The FDA's reassessment should go to public review sometime this year, Bolger says. But boiling it down to clear advice won't be easy:
• A difficult balance. The FDA estimates that bluefin tuna, prized by sushi lovers, contains 13 times the mercury of a farm-raised catfish. Yet tuna also is an oily fish that contains four to five times more omega-3 than lean catfish.
• Incomplete studies. People who have suffered heart attacks seem to lower future risk by eating more seafood. But does that benefit come from that extra salmon or from the cheeseburger not eaten? And might a heart patient do just as well by switching to chicken and a fish-oil supplement?
• Confusing detail. A few years back, the Florida Department of Health altered how its brochures ranked the mercury content of local species. It put the fish with the lowest amount at the top of the list instead of the bottom. None of the data changed, but the new format confused people around the office, says toxicologist Joe Sekerke, the department's mercury expert.
"Everyone said, 'Oh, I'm not going to eat any fish.' That was the exact opposite of what we were trying to say.''
Because of these difficulties, state and federal advisories focus on a few simple rules, like limiting seafood servings to two weekly for young women and children.
That reins in the mercury risk, but doesn't allow for extra benefits that three or four low-mercury fish servings might offer. That needs to change, Sekerke says.
"We are going to have to stop saying how many seafood (meals) you get a week and focus on how many omega-3 fatty acids you get,'' he says. "Don't ask me how it's going to be. But that's where we are going to have to end up.''
Toxic spills to Starkist
Small amounts of mercury occur naturally in the world's oceans. Land-based industrialization adds to the load.
Mercury works its way up the food chain and accumulates in fish tissue. Species with shorter lives, like salmon and shrimp, don't get so much. Longer living predators such as swordfish and grouper tend to load up.
The dangers of seafood mercury became painfully evident in Japan 50 years ago, when residents near the factory town of Minimata experienced numbness, brain damage and death. Cat bodies piled up; birds toppled from the sky. The culprit was a petrochemical plant that had dumped tons of mercury into a bay and polluted the region's primary food source.
That raises the question: If huge mercury doses can be fatal, what is the effect of small doses over time? Scientists couldn't ethically ask people to eat shark and swordfish at every meal to see if their speech would start to slur.
So they looked at island nations where people already ate lots of seafood. Fetal brain development was a particular concern, so studies focused on how mercury levels in pregnant women might affect their children's mental and motor skills after birth.
Though children in the Seychelles, near east Africa, showed no measurable effects, children in the Faroes, off Scandinavia, had slightly lower test scores as their mothers' mercury levels rose.
Using statistics from the Faroes, scientists from the U.S. Environmental Protection Agency picked a maternal mercury level where some children started having lower scores. To be extra cautious, the EPA then told U.S. women not to get within 1/10th of that mercury level.
That translated to the amount of mercury in two cans of light tuna. It is still a cornerstone of U.S. dietary policy.
In 2004, the EPA and FDA settled on a joint seafood advisory, directed only at children and women of child-bearing age, because they were perceived to be the most vulnerable population:
• Avoid four high-mercury species — shark, swordfish, tilefish and king mackerel.
• Eat a variety of seafood "low in mercury," but no more than two 6-ounce servings a week.
• If you eat two cans of tuna, only one can be albacore, which has three times the mercury of chunk light.
That was it. Nothing about men or older women. No guidance about "tweener fish'' like snapper or grouper whose mercury levels were too high for the low-mercury group but not as high as the "Do Not Eat'' group.
The two-serving limit, in particular, choked off choices that pose very little mercury risk. For example, canned light tuna qualified as a "low mercury'' meal, which pleased the tuna industry. But someone could also eat salmon, tilapia, sardines or shrimp every day of the week and still ingest less mercury than found in two cans of tuna.
Despite this variance, the EPA and FDA forged ahead with the two-fish limit on every species because focus groups showed that women would avoid seafood if the government offered too many choices. Who wants to take a risk with a baby?
"If we had made it on a sliding scale, like it's okay to eat lots of salmon, that might turn people to not eat any fish,'' says EPA biochemist Kate Mahaffey who helped draft the advisory. "It would be too confusing.''
But why two fish? Why not three or four, as long as people stick to the low-mercury types?
For one thing, the average American eats less than one seafood meal a week as it is. Setting an upper limit at two shouldn't constrain too many consumers.
Also, the American Heart Association was recommending that people eat at least two seafood servings a week because omega-3 fatty acids can promote cardiovascular health.
"We didn't want the public hearing too many messages,'' the FDA's Bolger says.
Two servings it was.
Beyond two servings
While the original island nation studies focused exclusively on mercury, others began to look at seafood's advantages — and the results were unsettling for the government's two-fish limit.
Scientists from Harvard University followed 135 pregnant women in eastern Massachusetts and tested their children's visual memory at age 6 months. The results, published in 2005, showed that when mothers ate more than two seafood meals a week, their children tested higher than the children of mothers who ate less. The more fish, the better the scores.
A study of more than 11,000 women in the United Kingdom, published last year, showed that children had lower verbal IQ's when their mothers ate less than two fish meals a week.
The Faroes study, which revealed the risk of maternal mercury, was re-evaluated to measure the benefits of seafood as well. In some cases, children performed better as their mothers' seafood intake rose.
"The issue is not whether methylmercury is toxic or not. The issue is whether we should eat fish or not,'' says Joe Hibbeln, lead author of the UK study and an acting chief of nutritional neuroscience at the U.S. National Institutes of Health. "The answer is, when looking at the risks and benefits of a unit of fish for child development, the benefits appear to strongly outweigh the toxic effects.''
The three studies have significant gaps.
The Boston study was small. Only nine women ate more than two seafood servings a week — hardly a ringing endorsement for all-you-eat seafood buffets.
The UK study did not measure mercury levels in mothers' hair or blood, the widely used methodology. So it lacked precision about some effects.
In the Faroes study, the seafood benefits would have been higher had the mothers not eaten so much pilot whale, a mammal high in mercury but low in omega-3.
The Institute of Medicine of the National Academy of Sciences recently concluded that the two-fish advisory is still "reasonable,'' even taking the UK and Boston data into account. But it calls for more research.
"We did not look at omega-3 four or five years ago when this was being debated,'' says Dr. Marion Aller, toxicologist and food safety director for the Florida Department of Agriculture. "The science on mercury continues to evolve as does some of the science on the benefits of fish.''
Hold the tuna
People listen to warnings about mercury.
Last month, the New York Times and an environmental group called Oceana reported that they had found high levels of mercury in sushi-grade tuna.
At Tokyo Sushi Cafe in St. St. Petersburg's BayWalk, tuna orders dropped from 30 to 50 pounds a week to 20, says owner Michael Chan. Since then, tuna consumption has picked up, but not all the way.
"I don't think it's that bad,'' says Chan, who estimates he might eat a few pounds of tuna a week himself. "I don't get sick.''
But Jane Hightower, a San Francisco internist who treats patients for mercury poisoning, thinks the government needs to extend the warnings to young adults, men and older women.
"They need to talk to everyone about it,'' she said. "When you do that targeted approach, it gives a green light to everyone else.''
The Institute of Medicine said some evidence indicates that men with higher mercury levels have more heart attacks.
St. Petersburg cardiologist Peter Wasserman, a spokesman for the American Heart Association, is more concerned about getting a lot of omega-3s into his patients. He recommends two fish servings a week, if not more, including tuna, which is loaded with omega-3s.
"I'd much rather they eat seafood than a big old steak,'' Wasserman says. "I think the risk of developing mercury poisoning is much less than developing heart disease, which is the No. 1 killer of women. There is a health care crisis with heart disease and yet we are picking things apart with mercury.''
Second time around
Elizabeth Martin, who gave up seafood for her first baby, is expecting again. She has read the advisories in pregnancy pamphlets. She knows which high-mercury fish to avoid.
But this time around, she's a little more relaxed. Shrimp and crab are beckoning and she's ready to give in.
"It's kind of an iffy subject,'' she says. "Every time you turn around, somebody's telling you something's bad for you.''