Food and Behaviour Research

Donate Log In

Choline - A Neglected Nutrient Vital for Healthy Brains - BOOK HERE

Total mercury exposure in early pregnancy has no adverse association with scholastic ability of the offspring particularly if the mother eats fish

Hibbeln J, Gregory S, Iles-Caven Y, Taylor CM, Emond A, Golding G (2018) Environ Int 116 108-115. doi: 10.1016/j.envint.2018.03.024. Epub 2018 Apr 14. 

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


There is a public perception that relatively low doses of mercury found in seafood are harmful to the fetal brain but little consistent evidence to support this.

In earlier publications we have shown no adverse associations between maternal total blood mercury levels and child behaviour, early development or cognitive function as measured by IQ.  However, for IQ the lack of adverse association was conditional upon the mother being a fish eater.

In this paper we analyse further data from the Avon Longitudinal Study of Parents and Children (ALSPAC), this time examining whether prenatal exposure to total mercury is associated with the child's scholastic abilities in reading, spelling, phoneme awareness, mathematics and science; the number of participants with prenatal mercury and relevant test results varied from 1500 to 2200. Multiple regression was used to assess relationships between prenatal total blood mercury concentrations and 16 different test results, after taking account of a variety of potential confounders; in parallel, logistic regression was used to determine associations with the risk of the child being in the lowest 15% of each score. Analyses were repeated stratifying for fish consumption and sex of the child.

There was no evidence of harm associated with the level of total mercury, provided the mother ate fish during pregnancy. This was particularly true for tests of mathematics and science.

We conclude that women should be confident that eating fish in pregnancy is beneficial for their unborn child.


This study confirms and extends earlier findings, showing that provided mothers eat fish and seafood, their total mercury levels during pregnancy are NOT linked with any harmful effects on their children's cognitive development.

Children's cognitive development was assessed here via many different measures of academic achievement recorded during their childhood - using comprehensive data from the UK birth cohort study 'ALSPAC' - The Avon Longitudinal Study of Parents and Children, which allowed the researchers to control for numerous other variables that could affect these outcomes.

These data support those from earlier studies, which found that

(1) the more fish and seafod mothers ate during pregnancy, the better was their children's development on a wide range of neurodevelopmental outcomes, including motor skills, social skills, and verbal IQ. See:

(2) higher maternal mercury levels in pregnancy were in fact associated with higher verbal IQ in their children - provided that the mother ate fish and seafood. 

Fish and seafood provides key brain nutrients essential to brain development but found in few other foods, including the long-chain omega-3 DHA, iodine, selenium and Vitamin D - as well as being an excellent source of zinc, B vitamins and high-quality protein.  These nutrients (particularly selenium) help the body to deal with toxins like methyl mercury. See:

These new data clearly show that mothers' mercury levels during pregnancy did not adversely affect the academic achievement of their children - procided that they ate fish and seafood.  

Since 2014, both the US FDA and the European Food Standards agency have recommended that women should aim to consume at least 2 portions of fish a week during their pregnancy - and that up to 4 portions per week is better for children's brain health than eating none.  However, fish and seafood intakes of pregnant women in most developed countries (and many developing ones) still fall far short of this target.

For more information on this subject, see the following list of articles, which is regularly updated: