Iodine intakes and main food sources in New Zealand adolescent males

Abstract

Background: The New Zealand population is susceptible to iodine deficiency due to low iodine levels in the soil. In response to this, two fortification strategies exist; iodisation of table salt which began in 1924, and more recently, in 2009, iodised salt was required to be used in most commercial bread products. Since the introduction of mandatory bread fortification in 2009, few studies have assessed the iodine intake of adolescents in particular. Objective: To estimate the usual iodine intake of adolescent males in New Zealand, and compare reported iodine intakes to nutrient reference values. To identify the main food sources contributing iodine to the diet, and determine the proportion of adolescent males using iodised salt in the household. Design: A cross-sectional survey of 15-18 year old adolescent males from high schools located in six locations across New Zealand. Iodine intake was assessed through two 24- hour dietary recalls, and were entered into FoodWorks to calculate energy and iodine intake and contribution of major food groups to iodine in the diet. Nutrient data were adjusted for ‘usual’ intake using the Multiple Source Method. A dietary habits questionnaire was used to determine the frequency of consumption for a range of foods, including those that are sources of iodine. Iodine intake was calculated from: food-only; from food and added iodised salt, where 48 μg iodine was added to participants who reported using iodised salt. Anthropometrical measurements were also taken. Results: Of the 135 participants included in the study, the majority (57%) identified as New Zealand European and other ethnicity, followed by Asian (32%), Māori (9%) and Pacific (2%). The mean energy intake was 10,077 kJ/day, and most participants (67%) were in the healthy weight category based on BMI z-scores. Fifty-seven percent of participants reported using iodised salt in their household. The mean iodine intake from food-only was 107 μg/day; the proportion of participants with usual iodine intake below the estimated average requirement of 95 μg/day was 31%. When iodine from iodised salt was included, the mean intake increased to 131 μg/day; the proportion of participants with an iodine intake below the estimated average requirement was 19%. Iodised salt users had a significantly higher iodine intake compared to non-users; the mean difference (95% CI) was 53 (44 to 62) μg/day. The dietary habits questionnaire revealed bread and bread-based dishes were the main contributors of iodine in the diet (31%), followed by milk and dairy products (19%). Conclusion: The majority of adolescent males surveyed in this study had a daily iodine intake that was adequate to meet their iodine requirements. The results from this study show iodised salt use and the mandatory fortification of bread with iodine continue to be important contributors of iodine in the New Zealand diet.