A new study published in The Journal of Nutrition concluded maternal iodine status does not explain differences in infant socio-emotional development.

Fish consumption during pregnancy has a significant influence on fetal growth and development but is particularly important for proper development of the brain and eyes. This has been largely attributed to the high amounts of omega-3 fatty acids in fish, and particularly to fish abundantly rich in docosahexaenoic acid (DHA). However, fish also provide a variety of other important nutrients needed in neurodevelopment such as iodine and vitamin D.  Iodine is critical for the production of thyroid hormones in normal growth and development of the fetal and infant brain, another plausible mechanism that links maternal fish consumption and child development.  Evidence shows that both low and high iodine intake during pregnancy is associated with poor neurodevelopment.

To examine whether maternal iodine status during pregnancy affects general and socio-emotional developmental trajectories before 11 months of age, Ingrid Kvestad (Regional Center for Child and Youth Mental Health and Child Welfare, NORCE Norwegian Research Centre) and colleagues at the Institute of Marine Research, Norway, conducted a randomized controlled trial. A total of 133 pregnant women were randomly assigned to receive 200 g cod fillet twice weekly (intervention group) or to continue with their habitual diet (control group) for 16 weeks during the second and third trimesters of pregnancy.  Fatty fish such as salmon and mackerel contain high amounts of omega-3 fatty acids, whereas lean fish such as cod are typically lower in omega-3 fatty acids but higher in iodine than other fish varieties. The trial included 3 follow-ups during pregnancy and 3 follow-ups postpartum when the infants were 2, 6, and 11 months old. The mothers completed a developmental screening questionnaire and a questionnaire to assess socio-emotional development.

An increased intake of lean fish during pregnancy did not improve maternal-reported general development during the first year of their infant’s life. However, mothers in the intervention group reported fewer socio-emotional problems in their children than did mothers in the control group, suggesting an effect of lean fish consumption on infant socio-emotional development.   Although mothers in the intervention group had higher iodine status after the cod intervention than others that continued with the habitual diet, maternal iodine status did not explain this difference.

A corresponding editorial by Beverly Muhlhausler (The University of Adelaide) emphasizes that dietary quality is important throughout pregnancy but there is limited evidence to suggest that increasing maternal fish consumption alone will significantly improve child neurodevelopmental outcomes.


Kvestad I, Hysing M, Kjellevold M, Naess S, Dahl L, Markhus MW.Maternal Cod Intake during Pregnancy and Infant Development in the First Year of Life: Secondary Analyses from a Randomized Controlled Trial. The Journal of Nutrition, Volume 151, Issue 7, July 2021, Pages 1879–1885, https://doi.org/10.1093/jn/nxab083.

Muhlhausler B.  Maternal Fish Intake and Infant Neurodevelopment: Causality or a Red Herring? The Journal of Nutrition, Volume 151, Issue 7, July 2021, Pages 1688–1689, https://doi.org/10.1093/jn/nxab143.

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