Prenatal Exposure to Nutrients in Fish May Protect Children Against Negative Effects of Mercury

A new study has found an association between eating fish during pregnancy and improvements in some measures of child development after birth, despite prenatal exposure to mercury from the fish. Published in the American Journal of Clinical Nutrition, the study tracked 1,265 mother-child pairs in the Republic of Seychelles, a country of islands that consumes 10 times more fish than the US. On average, pregnant mothers in the Seychelles eat fish about 12 times per week. For the study, researchers determined the mothers’ blood levels of mercury and certain nutrients, and then measured the children’s developmental progress when they were 20 months old. Here’s what they found:

  • Overall, there was no association between prenatal (not postnatal) mercury exposure and developmental outcomes in children.
  • Prenatal exposure to mercury was associated with lower Psychomotor Developmental Index (PDI) scores in children, but only in children whose mothers had a higher ratio of omega-6s in their diet.
  • For children whose mothers had a higher ratio of omega-3s—anti-inflammatory fatty acids found in fish—prenatal exposure to mercury was actually associated with improved PDI scores, suggesting that the higher levels of omega-3s from fish counteracted the higher exposure to mercury.
  • Nevertheless, DHA, a particular type of omega-3, was associated with higher scores for language development in children, but also with lower scores on the Mental Developmental Index, which measures sensory-perception, knowledge, and memory, among other things.

In general, the results are encouraging for soon-to-be mothers who want to get beneficial fats from fish, but are concerned about consuming toxins at the same time. Admittedly, the findings concerning DHA are somewhat puzzling, and may suggest that there needs to be a certain balance between DHA and other nutrients for optimal neurodevelopment. In adults, by contrast, several (but not all) placebo-controlled trials have found that DHA improves some measures of cognitive performance in both healthy people and in those with age-related cognitive decline.

Source: American Journal of Clinical Nutrition

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