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09-10-2012 | Psychology | Article

Contaminated fish pose dietary dilemma for pregnant women


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medwireNews: Exposure to low levels of mercury in utero increases a child's risk for developing attention deficit/hyperactivity disorder (ADHD), report researchers.

However, they also found that greater fish consumption during pregnancy was protective against ADHD, despite fish consumption being the most common route of mercury ingestion.

"These findings underscore the difficulties pregnant women face when trying to balance the nutritional benefits of fish intake with the potential detriments of low-level mercury exposure," said study author Susan Korrick (Harvard University, Boston, Massachusetts, USA) in a press statement.

The researchers analysed associations between ADHD behavior at the age of 8 years and maternal exposure to mercury in 604 children from a Massachusetts birth cohort, as measured by mercury levels in peripartum maternal hair (measurements available from 421 mothers), and maternal report of fish consumption (reports available from 515 mothers).

Writing in the Archives of Pediatric and Adolescent Medicine, lead author Sharon Sagiv (Boston University, Massachusetts, USA) and team report that levels of mercury in maternal hair ranged from 0.03-5.14 µg/g, with a median concentration of 0.45 µg/g, and were positively associated with ADHD.

There appeared to be a threshold effect at 1.00 µg/g, above which (n=66) each interquartile range increase in mercury in maternal hair raised the relative risk for ADHD in their children by a significant 70%. Notably, adjusting for total fish intake or omega-3 intake did not significantly change this association.

Regarding fish consumption, there was a significant protective effect against ADHD for children of women who consumed more than two servings of fish a week, who had a 60% lower relative risk for the condition than those whose mothers ate two or less fish servings a week. This association was still valid following adjustment for mercury level and other covariates.

These results present a dietary dilemma for pregnant women, as the US Food and Drug Administration currently recommend that they should consume no more than two portions of fish per week to minimise mercury ingestion.

The authors of the current study did not assess the types of fish most likely to be contaminated with mercury, but previous studies have shown shark, swordfish, king mackerel, and fresh tuna to have high mercury levels, whereas other types of fish such as salmon and haddock had lower levels.

"Women need to know that nutrients in fish are good for the brain of a developing fetus, but women need to be aware that high mercury levels in some fish pose a risk," commented Sagiv.

medwireNews ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012

By Helen Albert, Senior medwireNews Reporter

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