Iodine is an essential trace element and an integral part of the thyroid hormones, which play a role in the normal growth and development of the human body. A low intake of iodine can cause a spectrum of iodine deficiency disorders that may influence growth and development at different life stages, including goitre, cretinism, hypothyroidism, congenital abnormalities and impaired mental function.
Various strategies have been implemented to combat iodine deficiency including iodised oil, iodinated water, iodine supplementation and iodised salt. In September 2009, mandatory fortification of bread with iodised salt was introduced in New Zealand to address the re-emergence of mild iodine deficiency in children and adults that has been reported over the previous two decades. The aim of this study was to determine whether mandatory iodine fortification has improved iodine status in Dunedin adults.
This was a cross-sectional survey of 101 adult men and women aged 18-64 years living in Dunedin. Between July and November 2014, participants were asked to provide a spot urine sample and complete a questionnaire that included socio-demographic questions and an iodine-specific food frequency questionnaire (FFQ). Urine was analysed for iodine and creatinine and reported as median urinary iodine concentration (UIC) μg/L and urinary iodine:creatinine ratio (UI:Cr) μg/g. The iodine-specific FFQ was used to derive an estimate of iodine intake from bread and bread products, as well as an estimate of total daily iodine intake with and without the inclusion of discretionary iodised salt.
The median UIC for all adults was 75μg/L (females: 75μg/L and males: 81μg/L), indicative of mild iodine deficiency (i.e. 50-99μg/L) according to the World Health Organization (WHO)/United Nations Children’s Fund (UNICEF)/International Council for the Control of Iodine Deficiency Disorders (ICCIDD) population criteria. Estimated median iodine intake from the FFQ was 106μg/day from food without iodised salt and 129μg/day from food and iodised salt. Ethnicity was found to be associated with UIC (p=0.010); however, there was no association with either UIC or UI:Cr and bread iodine intake (p=0.457, 0.544), total iodine from food (p=0.215, 0.799) and iodised salt use (p=0.438, 0.596). Bread was the main contributor to iodine intakes, providing 54% and 70% of the estimated iodine intake for females and males, respectively. The median iodine intake from sliced bread, bread products and bread-based dishes was 55μg/day, with males having significantly higher iodine intake from bread compared to females (86 versus 41μg/day) (p<0.001).
In conclusion, this study has shown that compared to a median UIC of 53 μg/L in New Zealand adults before mandatory fortification, the median UIC in this convenience sample of Dunedin adults has increased to 75 μg/L, a classification of mild iodine deficiency. However, should the criteria suggested by a recent review be adopted, this sample would be classified as iodine sufficient.
