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. The NHS 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 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.
Women Stopped Eating Any Fish 'To be on the Safe Side'
The authors call for a change in official guidance. "Health advice to pregnant women concerning consumption of mercury-containing foods has resulted in anxiety, with subsequent avoidance of fish consumption during pregnancy." Seafood contains many nutrients crucial for children’s growth and development, but "there is the possibility that some women will stop eating any fish 'to be on the safe side'".
The authors said: "Although advice to pregnant women was generally that fish was good, the accompanying caveat was to avoid fish with high levels of mercury. Psychologically, the latter was the message that women remembered, and the general reaction has been for women to reduce their intake of all seafood."
Co-author Jean Golding, emeritus professor of paediatric and perinatal epidemiology at the University of Bristol, said: "It is important that advisories from health professionals revise their advice warning against eating certain species of fish. There is no evidence of harm from these fish, but there is evidence from different countries that such advice can cause confusion in pregnant women. The guidance for pregnancy should highlight 'Eat at least two portions of fish a week, one of which should be oily' – and omit all warnings that certain fish should not be eaten."
