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Fish in pregnancy not dangerous after all, says new study



A new study has called into question the decades-long official guidance advising pregnant women to limit consumption of certain fish because of their potentially high mercury content. That advice was based particularly on one 1997 study suggesting a correlation between fetal exposure to methylmercury and cognitive dysfunction at age 7.

The U.K’s National Health Service currently advises not only pregnant women but also all those who are potentially fertile (those “who are planning a pregnancy or may have a child one day”) to limit oily fish consumption to no more than two portions per week. During pregnancy and while trying to get pregnant, women are advised to avoid shark, swordfish, and marlin altogether.

Suspicions arose from study involving consumption of pilot whale

However, researchers from the University of Bristol (England) now suggest that assumptions generated by the original 1997 study – of a cohort of women in the Faroe Islands – were unwarranted. “It was clearly stated that the methylmercury levels were associated with consumption of pilot whale (a sea mammal, not a fish),” they said.

The pilot whale is a species known to concentrate cadmium and mercury, and indeed in 1989 Faroe Islanders themselves had been advised to limit consumption of both whale meat and blubber, and to abstain completely from liver and kidneys.

Yet, as the authors pointed out, following the 1997 study, “the subsequent assumptions were that seafood in general was responsible for increased mercury levels in the mother.”

New study shows ‘no evidence of harm’

Their new research, published in NeuroToxicology, has now shown that “there is no evidence of harm from these fish,” they said. They recommend that advice for pregnant women should now be revised.

The study drew together analyses on over 4,131 pregnant mothers from the Avon Longitudinal Study of Parents and Children (ALSPAC), also known as the ‘Children of the 90s’ study, with similar detailed studies conducted in the Seychelles. The two populations differ considerably in their frequency of fish consumption: fish is a major component of the diet in the Seychelles, but eaten less frequently in the Avon study area, centered on Bristol.

The team looked for studies using the data from these two contrasting cohorts where mercury levels had been measured during pregnancy and the children followed up at frequent intervals during their childhood. Longitudinal studies in the Seychelles “have not demonstrated harmful cognitive effects in children with increasing maternal mercury levels”, they reported.

The same proved true in the United Kingdom, a more-developed country where fish is eaten less frequently, they found. They summarized the results from various papers that used ALSPAC data and found no adverse associations between total mercury levels measured in maternal whole blood and umbilical cord tissue with children’s cognitive development, in terms of either IQ or scholastic abilities.

In addition, extensive dietary questionnaires during pregnancy had allowed estimates of total fish intake to be calculated, as well as variations in the amount of each type of seafood consumed. “Although seafood is a source of dietary mercury, it appeared to explain a relatively small proportion (9%) of the variation in total blood mercury in our U.K. study population,” they said – actually less than the variance attributable to socio-demographic characteristics of the mother (10.4%).


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