Dietary iodine deficiency in the Gippsland region of Victoria, Australia

Background Iodine is an essential micronutrient for the production of thyroid hormones and normal neurodevelopment. A deficiency in iodine causes a number of defects collectively known as Iodine Deficiency Disorder (IDD). Even mild iodine deficiency in pregnancy is a risk factor for babies as it may result in impaired intellectual development; this is the most serious consequence of mild to moderate dietary iodine deficiency. Australia overall is iodine deficient. However, in the National Iodine Nutrition Study (NINS), Victoria had the worst status with regard to iodine deficiency in school children. The Gippsland region of Victoria has a long history of iodine deficiency. In 1960, Gippsland was described in a WHO monograph series on endemic goitre as the ‘home of goitre’ in Victoria. Despite this history the Gippsland population has not been screened for iodine deficiency since 1948. In response to this data we devised a four part study to provide details of the current regional and sub regional iodine status of Gippsland. Hypothesis There is a recurrence of dietary iodine deficiency in the Gippsland region. Objective The research plan initially included three objectives • To examine the historical evidence of dietary Iodine deficiency. • To research environmental iodine status. • To estimate the population iodine status and factors affecting it. Two further objectives were added during the project • To develop an effective and easy method to regularly analyse and monitor the iodine status (deficiency) of pregnant women and their new born babies. • To measure the effect on the iodine status of a cohort of Gippsland pregnant women of the recently commenced Food Standards of Australia and New Zealand (FSANZ) nationwide bread iodine fortification program. Methods This is a four part study using different methods to test our hypothesis: • Part 1: Search for historical evidence of iodine deficiency using archival research, rare book and journal collection searches and asking for Gippsland people to recall previous iodine supplementation programs they may have participated in. • Part 2: Research for environmental evidence of iodine deficiency by measuring the iodine concentration of drinking water from 18 water treatment plants and rain water tanks across central, west and south Gippsland. • Part 3: Victorian (including Gippsland) Neonatal population iodine status estimation by retrospective neonatal Thyroid Stimulating Hormone (TSH) data analysis from 2001 to 2006. • Part 4: Gippsland pregnant women iodine status estimation by urinary iodine concentration measurement and an exploration of factors influencing iodine status during pregnancy by application of a self-reported food questionnaire. Results There was an iodine tablet supplementation program in Gippsland schools from the late 1940s to late 1960s. Gippsland drinking water shows an iodine concentration indicative of environmental iodine deficiency. Analysis of the Victorian neonatal Thyroid Stimulating Hormone (TSH) database from 2001 to 2006 shows that the incidence of iodine deficiency is increasing in Gippsland and Victoria among newborns at the population level. The urinary iodine concentration in a cohort of Gippsland pregnant women indicates an inadequate intake of iodine during pregnancy and that the bread iodine fortification program appears to be ineffective in this cohort. Conclusion Results from this study indicate that dietary iodine deficiency is a reemerging problem in the Gippsland region. In Gippsland the assumption of the average Australian population daily intake of iodine through drinking water by FSANZ is misleading and FSANZ needs to take account of regional variation when calculating the influence of this critical dietary component. The current iodine fortification program needs to be extended to other foods and focus on the prevention of iodine deficiency during pregnancy. Neonatal TSH levels should be used to monitor the Australian population iodine (deficiency) status and the effectiveness of fortification, especially in the population groups most at risk of iodine deficiency.