Urinary iodine concentration of New Zealand adults improves with mandatory fortification of bread with iodised salt but not to predicted levels.

Abstract

To measure the iodine status and iodine intake of New Zealand adults 18-64 years of age following mandatory fortification of bread with iodine. A cross-sectional survey of NZ adults living in Dunedin and Wellington during February-November 2012. Three hundred and one men and women aged 18-64 years randomly selected from the New Zealand Electoral Roll completed a 24-h urine collection, a demographic and iodine-specific food frequency questionnaire (FFQ), and had height and weight measured. Urine collections were analysed for iodine and reported as median urinary iodine concentration (UIC) µg/L and median urinary iodine excretion (UIE) µg/day. The FFQ was used to estimate iodine intake with and without discretionary iodised salt use. The median UIC for all adults was 73 µg/L, indicative of mild iodine deficiency. The mean urinary volume was 2.0 L. As an estimate of iodine intake, the median UIE was 127 µg/day. Estimated iodine intake, using the FFQ which included discretionary iodised salt use, was 132 µg/day. Iodine intakes were associated with UIC (P = 0.040) and UIE (P = 0.003), but not with bread iodine intake and iodised salt use. Using the WHO/UNICEF/ICCIDD target for iodine sufficiency (a UIC of >100 µg/L) based on school-aged children with a mean urinary volume of 1.0 L, the iodine status of NZ adults does not reach adequate levels (73 µg/L). A more realistic parameter in a population with a higher urinary volume excretion (2.0 L) is the UIE. A median UIE of 127 µg/day suggests that the iodine status of NZ adults is now likely to be adequate.