Are breast-fed infants and toddlers in New Zealand at risk of iodine deficiency?

Objective This study assessed the iodine status of New Zealand infants and toddlers and explored factors that might influence their iodine status. Methods A community-based, cross-sectional survey of 6- to 24-mo-old children was conducted in three cities in the South Island of New Zealand. Iodine status was determined by a casual urine sample. Breast-feeding mothers were asked to provide a breast milk sample for iodine determination. Caregivers collected a 3-d weighed diet record from their children to investigate associations between dietary patterns and urinary iodine excretion. Results The median urinary iodine concentration for the group (n = 230) was 67 μg/L (interquartile range 37–115) with 37% (95% confidence interval 30.5–43.4) of children having a urinary iodine concentration lower than 50 μg/L. When children were classified by current feeding method, those children who were currently formula-fed had a significantly higher median urinary iodine concentration (99 μg/L) than did children who were currently breast-fed (44 μg/L; P < 0.000). The mean iodine concentration in breast milk was 22 μg/L (n = 39). After multivariate analysis using estimates from 3-d diet records, only percentage of energy from infant formula was significantly associated with urinary iodine concentration (P = 0.005). Conclusions This study found mild iodine deficiency in a group of New Zealand infants and toddlers. Children who consumed infant formula, which is fortified with iodine, had better iodine status than did children who were currently breast-fed because breast milk contained low levels of iodine.