Study of Mercury and Fish to Focus on Teenagers

September 19, 2005

Rochester scientists and doctors are heading to a beautiful tropical island to examine a group of islanders in a study that has implications for anyone in the world who enjoys the taste of seafood.

The team is beginning the latest phase of one of the longest-running studies ever to follow the health of a group of people over many years. The 16-year study of more than 700 children in the Seychelles Islands, a tiny island nation in the Indian Ocean, is looking at whether small amounts of mercury in ocean fish such as tuna and swordfish are harmful to people.

The issue has been hotly debated, with environmentalists claiming that hundreds of thousands of U.S. children are at risk of serious neurological impairment because their mothers ate fish containing mercury during pregnancy. So far, though, scientists at the University of Rochester Medical Center who are doing the study have not observed any adverse effects among children whose mothers ate, on average, 12 meals of fish each week during pregnancy. That is about 10 times as much fish as most Americans eat.

Researchers first designed the study back when Ronald Reagan was president, to determine if pre-natal exposure to low levels of mercury from fish consumption had effects on child development. The team received funding from the National Institute of Environmental Health Sciences and began studying children born in the Seychelles in 1989 and 1990. Since then, investigators have examined the children six times, and each time there has not been evidence that low levels of mercury cause health problems.

Now the study is continuing for five more years, thanks to another round of funding from NIEHS, which recently awarded the group $3.4 million to evaluate the children as teenagers.

The project is currently headed by Philip Davidson, Ph.D., professor of Pediatrics and chief of the Strong Center for Developmental Disabilities at Golisano Children’s Hospital at Strong.

While mercury is certainly toxic at high levels, the investigators are looking particularly at whether the low levels found in ocean fish cause harm. People receive most of their exposure to methyl mercury, which comes from both natural and man-made sources, by eating ocean fish like tuna, swordfish and shark. Ocean fish around the world have approximately the same levels of mercury; seafood eaten in the Seychelles has about the same amount as that eaten in New York.

When scientists first began the project, known as the Seychelles Child Development Study, they thought it likely that they’d find developmental and other problems in children of mothers who ate a great deal of fish. So far they’ve detected no such problems. However, recent evidence in animals suggests that learning, memory and behavioral problems linked to mercury might begin in adolescence.

“The body of evidence so far indicates that there are not detectable effects in young children. But we don’t know about older children until we study them,” said Davidson. “There is no question that many chemicals and contaminants are neurotoxic. The real question is whether the actual exposure has enough of an effect to be relevant. We’re talking about very small dosages of mercury, and we’re looking for a very small effect. There may be none.”

Davidson and several other Medical Center researchers are making regular trips to the Seychelles to begin a rigorous examination of the children at age 15. Each child will receive a thorough medical and psychological exam, along with some physiological tests of hearing and heart rate. The team will perform sophisticated tests to assess the health of the nervous system and traits such as concentration, attention span, problem-solving abilities, intelligence, and motor skills. Children will also be interviewed about behaviors such as smoking and drinking alcohol and how well they get along with others, and they’ll be checked for signs of autism. The children will be examined again in two years.

In the past, the team did extensive evaluations in the Seychelles, then carted back all the data to Rochester in bulging suitcases, where it was entered into computers. Now, workers in the Seychelles will enter data directly using handheld devices.

The Seychelles study is rooted in previous work by the Rochester team, which put together the first precise data showing that pre-natal exposure to mercury could harm a developing child. Their study of the victims of an accidental mercury poisoning event in Iraq more than 30 years ago spurred them to start the Seychelles study to try to pinpoint the levels at which mercury poses a danger. They chose the Seychelles for several reasons: People there eat a lot of fish, there are no local sources of mercury pollution, and most people born on the islands stay there, making the population easy to track over a number of years.

The findings from the Seychelles have led the team to weigh the benefits of nutrition from fish against the risks of small levels of exposure to mercury. Is it possible that avoiding fish during pregnancy could hurt children more than any risk from mercury? To answer that question, the Rochester team has been working with scientists at the University of Ulster in Ireland, tracking the health and dietary habits of 300 people in the Seychelles. The team has tracked how much fish mothers-to-be ate during pregnancy, and then examined their children several times, looking not only at mercury but also at other dietary factors like breastfeeding and blood levels of iron, selenium, and thyroid hormone. The team is currently analyzing its results and hopes to begin a second five-year phase of that study, through a program funded by the European Economic Union.

For 15 years the study has been conducted by a team led by Thomas Clarkson, Ph.D., neurologist Gary Myers, M.D., and Davidson. The team also includes pediatrician Jonathan Klein, M.D.; dentist Gene Watson, D.D.S., Ph.D.; scientist Bernard Weiss, Ph.D.; biostatistician Li-Shan Huang, Ph.D.; epidemiologist Edwin Van Wijngaarden, Ph.D.; Tristram Smith, Ph.D.; biochemist Elsa Cernichiari; Jean Reeves; technician Margaret Langdon; and data entry clerk Kyla Barrons. Also taking part are scientists Andre Leste and Conrad Shamlaye of the Republic of the Seychelles; and former Rochester faculty members Deborah Cory-Slechta, Ph.D., now at Rutgers, and Christopher Cox, Ph.D., now at the National Institutes of Health.

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