The study, published in The Journal of Nutrition, was a collaboration between the Norwegian institute of Public Health, Oslo and Akershus University College of Applied Sciences and TINE SA and used data from the Norwegian Mother and Child Cohort Study (MoBA).
They found that children whose mothers had low dietary iodine intakes during pregnancy were more likely to experience various symptoms of impaired brain development.
“Maternal iodine intake below the Estimated Average Requirement (EAR) during pregnancy was associated with symptoms of child language delay, behaviour problems, and reduced fine motor skills at 3 y of age,” concluded lead author Marianne Abel from the Research and Development department of TINE SA.
In the main analysis, the study evaluated iodine intake solely from food. Participants were divided into those consuming either less than, or more than 160 micrograms per day (ug/d), the EAR recommended by the National Academy of Medicine (formerly the Institute of Medicine)
The study also observed a dose –response relationship between maternal iodine intake and behavioural problems, with odds ratio for this outcome rising particularly steeply for dietary intakes below 100 ug/d.
“The results of this study emphasize the urgent need for preventing inadequate iodine intake in women of childbearing age to secure optimal brain development in children,” recommended Abel.
No benefit from supplements
The team also carried out separate analysis on mothers taking iodine supplements of up to 200 ug/d.
“The results showed no evidence of a protective effect of iodine supplementation during pregnancy,” commented the researchers.
For mothers in the low intake group (<160 ug/d), supplementation was linked to negative effects.
“In those reporting first use in gestational weeks 0–12, supplement use was associated with an increased risk of externalising behaviour problems,” reported the researchers.
Similarly, starting supplementation in the second trimester was linked to a higher risk of internalising behaviour problems.
The study authors speculated on various possible reasons for the lack of beneficial, and potentially harmful, effects of supplementation.
“Initiating supplement use during pregnancy might be too late and may also provide less iodine than needed to compensate for the effects of a depleted iodine store on thyroid function,” they suggested.
“A sudden increase in iodine intake [from supplements], although modest and within the recommendations, might also lead to a ‘stunning effect,’ with transient inhibition of maternal or foetal thyroid hormone production.”
Iodine intake measurement
In the study, researchers used iodine consumption calculated from a Food Frequency Questionnaire (FFQ) (specifically designed for MoBa) to measure intake, rather than Urinary Iodine Concentration (UIC). Validation studies showed a good correlation between the two exposure measures, indicating that FFQ is an adequate long-term measure for iodine status.
“FFQ correlation coefficients for the calculated iodine intake and major iodine food sources were higher than for most other foods and nutrients, indicating a regular consumption pattern of food items containing iodine,” wrote the researchers.
Long-term dietary intake
The researchers emphasised the importance of long-term, rather than short-term iodine status; and that securing long-term adequate dietary (rather than supplemental) intake before pregnancy is essential to promote healthy brain development in children.
Source: The Journal of Nutrition
Volume 147, issue 7. Pages 1314-1324 doi: 10.3945/jn.117.250456
“Suboptimal Maternal Iodine Intake Is Associated with Impaired Child Neurodevelopment at 3 Years of Age in the Norwegian Mother and Child Cohort Study”
Authors: Marianne H Abel, Anne-Lise Brantsaeter et al