The iodine status of New Zealand school children post-fortification of bread with iodine

Abstract

Abstract Background: Iodine deficiency is a common nutrient deficiency in many parts of the world and is of concern due to the importance of the thyroid hormones for growth and development of children. Iodised salt was introduced as a straightforward solution to correcting iodine deficiency, and has been successful in many countries for the lastcentury. However iodine deficiency has re-emerged in many parts of the world including developed countries such as New Zealand (NZ) and Australia. This is thought to be due to the lack of use of iodised salt in production, and public health messages to reduce salt intakes. In response to the re-emergence of iodine deficiency in NZ and Australia, their governments worked together to introduce mandatory fortification of bread with iodine in 2009 to improve iodine intakes in both countries. The aim of this study was to assess the iodine status of NZ school children following mandatory fortification of bread with iodine. Methods and Procedures: A school-based cluster survey was used to randomly select schools from two NZ cities (Auckland or Christchurch) during February and March 2015. Children aged 8-10 were invited to participate and were given information packs to take home, containing consent forms for the parents and child. Consenting children completed a general questionnaire about their demographic information and health and a short iodine-specific food frequency questionnaire (FFQ). Height and weight was also taken and children were asked to provide a urine sample for determination of urinary iodine concentration (UIC) and a finger prick blood sample for determination of Thyroglobulin (Tg). Results: The median Urinary Iodine Concentration (UIC) of the children (n 415) was 116μg/L, with only 5% of children having a UIC below 50μg/L and 39% had below 100μg/L indicating sufficient iodine status (median UIC of 100-199μg/L). Males had significantly higher UIC than females with a mean UIC value of 126μg/L compared to 107μg/L (p=<0.001). Children of Asian ethnicity had significantly higher UIC than Māori or NZEO children with a mean UIC value of 151μg/L compared to 109μg/L and 110μg/L respectively (p=0.006). There was no association found between UIC and age, the type of salt used or school decile. The FFQ was used to estimate iodine intakes with and without discretionary iodised salt use. The estimated average iodine intakes of children including iodised salt were 101μg/day, which is an improvement of approximately 35% since pre fortification. However, nearly a quarter of children had an iodine intake less than the estimated average requirement (EAR) of 65μg/day for 8 year olds and 75μg/day for 9-10 year olds. Bread and bread products was the major source of iodine in the diet of children contributing 50% of iodine intakes. The results of Tg will not be presented in this thesis. Summary/conclusion: The improved UIC and iodine intakes seen in children are likely to be the result of the addition of iodised salt to bread. Given that the median UIC remains on the low end of the adequate range and nearly one quarter of children had low iodine intakes, further food products may need to be fortified to ensure optimal iodine status in NZ school children.