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

Abstract

BackgroundConflicting 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.MethodsPregnant women (median prenatal blood mercury 1.86 μg/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.ResultsBefore 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.ConclusionThe relationship between intrauterine exposure to mercury and offspring IQ appears to be benign provided the mother consumes fish.

Relationships between seafood consumption during pregnancy and childhood and neurocognitive development: Two systematic reviews

“…They represent 24 unique cohorts that met the criteria for inclusion and did not meet criteria for exclusion for this question. Of these 29 studies, seven were conducted in the United States [15,20,22,27,32,34,37]; seven in the United Kingdom [13,14,17,19,35,38,39]; three in Spain [23,31,36]; two in Italy [28,29] three in the Republic of the Seychelles [18,25,26]; and one each in Denmark [21], Norway [40], the Netherlands [33], China [30], Japan [24], the Faroe Islands [16] and another in a consortium of European countries [41]. The sample sizes ranged from 135 [15] to 38,581 mother-child pairs [40] with a median sample size of 498 mother child pairs [24].…”

“…Ten studies reported that the FFQ provided prompts for frequency, e.g. "less than once per week," or "more than once per day" [15,17,19,22,29,31,32,35,37,39]. Two studies reported administering an FFQ during first trimester [31,36].…”

Mercury exposure and its effects on fertility and pregnancy outcome

“…The role of Hg as a toxicant in sexual reproduction and pregnancy is quite neglected compared with the great attention spent on reports regarding neurotoxicology from this heavy metal. Despite some contradictory evidence, the role of Hg in human reproduction is going to be a major alarming issue . This MiniReview is aimed at analysing the published documentation about the effects of organic and inorganic Hg in human fertility, the outcome of childbirth, congenital abnormalities, loss of pregnancy and menstrual disorders.…”

“…Despite some contradictory evidence, the role of Hg in human reproduction is going to be a major alarming issue. [32][33][34][35][36][37] This MiniReview is aimed at analysing the published documentation about the effects of organic and inorganic Hg in human fertility, the outcome of childbirth, congenital abnormalities, loss of pregnancy and menstrual disorders.…”

An abundance of seafood consumption studies presents new opportunities to evaluate effects on neurocognitive development

“…A recent study in the United Kingdom found that children of mothers who had eaten no seafood but had still been exposed to mercury showed a trend toward lower IQ scores while children of mothers who had eaten seafood and had been exposed to the same levels of mercury experienced gains in IQ [40]. Like the Seychelles and Faroe Islands results when compared against each other, this study suggests that the nutrients in seafood can cause seafood to be beneficial notwithstanding the presence of mercury that could otherwise cause a decline in neurocognitive test results.…”