Thyroid hormone and ADHD

Low maternal levels of thyroid hormone during pregnancy increase the risk of neurocognitive problems – including language and cognitive delays, poor psychomotor skills and autistic traits – in children. Now, new research suggests that mild thyroid hormone insufficiency during pregnancy might increase the risk of attention deficit hyperactivity disorder (ADHD).

Researchers enrolled 3873 pairs of children and carers. Maternal thyroid hormone levels had been measured after a mean of 13.6 weeks gestation. They adjusted for potential confounders, such as sex, ethnicity, maternal age, education and income.

About 3% of mothers (n=127) showed hypothyroxinemia during early pregnancy. Average ADHD symptom scores at eight years of age were 7% higher in children born to hypothyroxinemic mothers. Similar results emerged after excluding women with raised levels of thyroid peroxidase antibodies (8%) – implicated in autoimmune thyroid disease – and following adjustment for children's IQ (6%) or autistic symptoms (7%). Neuroimaging and animal studies should now investigate the underlying mechanisms.