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Maternal prenatal blood mercury is not adversely associated with offspring IQ at 8 years provided the mother eats fish: A British prebirth cohort study

Golding J, Hibbeln JR, Gregory SM, Iles-Caven Y, Emond A, Taylor CM. (2017) Int J Hyg Environ Health 220(7) 1161-1167. doi: 10.1016/j.ijheh.2017.07.004. 

Web URL: Read this and related abstracts on PubMed here. Free full text of this article is available online



Conflicting evidence concerning possible harm from mercury (Hg) in regard to offspring cognition if the woman eats fish has prompted this study to examine evidence from a British pre-birth cohort to investigate the relationship between the two.


Pregnant women (median prenatal blood mercury 1.86μg/L) resident in the study area with delivery between April 1991 and December 1992 were followed up and verbal, performance and total intelligence quotient (IQ) of 2062 offspring were measured at age 8.  Analysis treated IQ as (a) continuous and (b) the lowest 25% of the distribution. Multiple and logistic regression analyses took account of social and demographic variables. Stratification considered children of fish eaters separately.


Before adjustment, mean full-scale IQ increased with increasing Hg (change with 1SD of Hg=+2.02; 95%CI+1.40,+2.64 IQ points; P <0.0001); after adjustment effect size was reduced although still positive (+0.61;95%CI -0.06,+1.29 IQ points; P=0.073).

The adjusted positive relationship was stronger when fish-eating mothers were considered separately (+0.84:95%CI +0.13,+1.56 IQ points; P=0.021) in comparison with the outcomes for non-fish eaters, where the adjusted relationship was negative (-2.22;95%CI -5.00,+0.56 IQ points; P=0.117). 

The binary outcome showed a similar pattern with the adjusted OR for non-fish-eaters 1.79 (95%CI 1.10,2.93; P=0.019) per SD of Hg, significantly different from that for fish consumers (0.94;95%CI:0.82,1.08)(Pinteraction<0.05).  There were no differences between the sexes in the associations, nor did the level of the mother's blood selenium change the effect sizes.

Conclusion: The relationship between intrauterine exposure to mercury and offspring IQ appears to be benign provided the mother consumes fish.


Good evidence has already shown that a higher intake of fish and seafood by mothers during pregnancy leads to better brain health and development in thier children - in terms of their cognition (verbal IQ), behaviour, social skills and almost all other outcomes.  See:

These benefits are thought to reflect the fact that fish is a uniquely rich source of the key long-chain omega-3 fats (EPA and DHA) - essential for normal brain development and function, but lacking from most modern, western-type diets.

Fish and seafood are also important sources of other key nutrents including iodine, selenium and Vitamin D - each of which is also essential to normal brain development and health, and yet many mothers-to-be have sub-optimal status of these nutrients too.  

Despite the overwhelming evidence, many mothers-to-be themselves continue to worry about eating fish during pregnancy, and both professionals and public health authorities still issue cautionary advice about the possible harms, in terms of its potential mercury content.

Although some types of fish and seafood can contain traces of mercury, most of the total body burden of this neurotoxic mineral actually comes from industrial pollution, and dental amalgam fillings, so that dietary fish intake is in fact only a minor source.  

Most importantly, key nutrients provided by fish and seafood (and few other foods) - particularly selenium - actually help to protect against the potentially toxic effects of any mercury that fish and seafood may provide.

This new study found that

  • higher maternal mercury levels in pregnancy actually predicted better cognitive outcomes in chilldren - provided that mothers were consuming fish.
The data came from the world-leading 'Children of the 90s' UK birth cohort study, ALSPAC - so the researchers were able to control for numerous other potentially confounding factors known to affect children's IQ.

The benefits of fish consumption during pregnancy thus appear to more than compensate for any potential risks from mercury.

These findings therefore fully support previous research in showng that in order to maximise their children's brain health and intelligence, mothers should be encouraged to eat more fish during pregnancy, not less.

For more articles on this subject, see: