An association has been reported between levels of maternal thyroid hormone during early pregnancy and higher scores for ADHD symptoms in children.
While ADHD has a genetic component, there are environmental factors that can affect fetal neurodevelopment, increasing the risk of a child developing ADHD. Environmental factors that have been shown to increase risk of ADHD include exposure to cigarette smoke, and premature birth.
Hypothyroxinemia, a reduction in thyroid hormone levels, can occur during pregnancy, even in women who have normal thyroid function. This can have implications on fetal neurodevelopment, since thyroid hormone is important for proper development of the central nervous system. The fetus does not begin to produce its own thyroid hormone until mid-gestation, therefore maternal thyroid hormone is crucial during these early stages of fetal development.
Researchers from the Netherlands have studied the association between ADHD and low thyroid hormone during early pregnancy. The study, reported in the Journal of the American Medical Association, found an association between low thyroid hormone levels in early pregnancy and symptoms of ADHD in children at 8 years of age. Low thyroid hormone levels in early pregnancy were associated with a 7% increase in ADHD symptoms scores in these children. The results remained unchanged when taking into account other factors such as ethnicity, sex, maternal age, maternal education level, or income.
The finding that hypothyroxinemia during early pregnancy is associated with an increase in ADHD symptoms in children confirms the important role of thyroid hormone during fetal neurodevelopment. The authors suggest that future research should be directed at identifying the mechanisms that play a role in this association.
Modesto T, Tiemeier H, Peeters RP, Jaddoe VW, Hofman A, Verhulst FC, Ghassabian A. “Maternal Mild Thyroid Hormone Insufficiency in Early Pregnancy and Attention-Deficit/Hyperactivity Disorder Symptoms in Children.” JAMA Pediatr. 2015 Jul 6. doi: 10.1001/jamapediatrics.2015.0498. [Epub ahead of print]
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Written by Deborah Tallarigo, PhD