The recommended intake of iodine during pregnancy is 250 µg/day (1). Iodine is a crucial micronutrient for offspring brain development, and previous research has shown that iodine deficiency can negatively influence offspring neurodevelopment (2,3). This analysis examines the relationship between maternal iodine intake during pregnancy and behavioural difficulties in children at 81 months (6.75 years).

Women were from the Avon Longitudinal Study of Parents and Children (ALSPAC) who had singleton pregnancies and iodine intake data. Iodine intake was assessed at 32 weeks of gestation using a food frequency questionnaire (FFQ) (4) (n = 11,748). Behavioural difficulties at 81 months were assessed using the Strengths and Difficulties Questionnaire (SDQ), including prosocial, hyperactivity, emotional, conduct, peer and total difficulties.

Linear and non-linear regressions were used to explore the relationships after adjusting for confounders based on previous literature and a directed acyclic graph (pre-pregnancy body mass index, intake of goitrogen-rich foods, alcohol intake, maternal and paternal education level, parity, age of mother at last menstrual period and energy intake).

Likelihood ratio tests suggested that maternal iodine intake was non-linearly associated with peer (χ2(1) = 303.66, p = 4.95E-38) and total behavioural difficulties (χ2(1) = 178.61, p = 2.39E-16). Restricted cubic spline plots indicated there was an L-shaped relationship where iodine intake ≥150 µg/d was associated with lower behavioural scores (peer and total) (i.e. fewer behavioural difficulties) and intakes below 120 µg/g were associated with higher behavioural scores (i.e. more behavioural difficulties). Total behavioural scores steadily increased beyond intakes of 200 µg/d.

Maternal iodine intake at 150-200 µg/d during pregnancy was associated with fewer peer and total behavioural difficulties in later childhood, reinforcing the importance of maintaining iodine intakes in pregnant women. However, excessive intake may have detrimental effects, in line with previous research in a Norwegian cohort (outcomes at 3 years old) (3). Future research should investigate the mechanisms underlying this association and consider how offspring iodine intake may moderate this association.