Study of high-seafood diet points to poison's long-lasting impact.
Eating seafood that contains mercury can affect the brain development of children in their adolescence, according to a study of people in the Faroe Islands.
The study fuels an ongoing debate about the health effects of a form of mercury called methylmercury, which accumulates in large marine animals such as swordfish and whales.
Researcher know that these compounds are toxic to babies as they grow in the womb, but there has been little evidence that older children also suffer developmental problems after exposure to the poison.
This could change after a study of the health of children on the Faroe Islands in the North Atlantic, where inhabitants eat lots of seafood and whale meat and so are exposed to relatively high levels of mercury.
The group previously found that the children, when 7 years of age, had a slower transmission of electrical signals along a particular circuit in their brain than normal. Now that the children are 14 years old, after a continued diet of fish and whale meat, the researchers find that this disruption is even worse1. They also found evidence that mercury exposure is linked to subtle difficulties in controlling blood pressure2.
The findings suggest that any harm done by mercury before birth or in early childhood was not repaired as the children grew up. And continued mercury exposure may continue to affect the brains of teenagers, says team leader Philippe Grandjean of Harvard School of Public Health in Boston, Massachusetts.
At the moment, the US Food and Drug Administration (FDA) advises pregnant women, nursing mothers and young children to avoid eating shark, swordfish, king mackerel and tilefish, in order to keep mercury intakes low. But Grandjean suggests that safety messages about mercury should highlight the toxin's potential impact on older children as well.
Others are not convinced that a wider warning is needed. The Faroe Islanders are virtually unique in their whale-rich diet, says Gary Myers, who studies mercury exposure at the University of Rochester in New York. So it doesn't make sense to extend the study's results to other populations, he says.
In addition, Myers says, there may be other toxins in whale meat such as PCBs and dioxins that might explain some of the detrimental effects. "Some people are convinced that mercury causes these effects and others are not so confident," he says.
Mercury leaches into water from natural sources, such as eroding rocks, and from industrial pollution such as coal-fired power stations and incinerators.
“Some people are convinced mercury causes these effects and others are not so confident Gary Myers , University of Rochester”
The chemical's toxicity was tragically illustrated in the 1950s and 60s, when residents of Minamata Bay in Japan suffered chronic mercury poisoning from water pollution. The high doses of mercury interfered with fetus development, causing many children to be born with malformations.
Scientists are still debating whether low levels of mercury in seafood are also harmful. The Faroes study, which involves more than 1,000 participants, is one of two large investigations into the long-term health effects of mercury exposure from eating fish. The second, being carried out in the Seychelles by Myers and his colleagues, has found little evidence that it causes harm.
Regulatory agencies have to balance concerns about exposure to mercury with arguments for encouraging the consumption of seafood, based on its healthy nutrients, says Joseph Hibbeln of the US National Institutes of Health in Bethesda, Maryland, who studies the effects of fish on health.
Murata, K. et al. Delayed brainstem audietory evoked potential latencies in 14 year old children exposed to methylmercury. Journal of Pediatrics, doi:10.1016/j.jpeds.2003.10.059 (2004).
Grandjean, P., Murata, K., Budtz-Jorgensen, E. & Weihe, P. Cardia autonomic activity in methylmercury neurotoxicity: 14 year follow-up of Faroese birth cohort. Journal of Pediatrics, doi:10.1016/j.jpeds.2003.10.058 (2004).
University of Rochester