Refinements to Assessment of Iodine Nutrition

Abstract

Objectives: The main target groups of iodine programs are pregnant women (PW) and non-pregnant women of reproductive age (NPW), yet surveys frequently focus on school age children (SAC). It is unclear whether median urinary iodine concentration (mUIC) in SAC can be used as a surrogate for PW and NPW. It is also unclear what range of iodine intake is adequate in SAC. The objectives of this research were to: 1) Compare mUIC values in SAC with those in PW and NPW; and 2) determine if the current mUIC range for SAC is appropriate by assessing thyroglobulin (Tg), a functional biomarker of iodine status. Methods: 1) The Iodine Task Force (ITF) reviewed surveys where mUIC in SAC, PW, and NPW were available and compared iodine status across groups; and 2) for determining the adequate range of mUIC in SAC, the ITF analyzed and interpreted a multicenter study. Results: 1) When SAC had adequate or above adequate iodine status, PW were inadequate in 47% of the surveys. 2) In SAC, the two current WHO/UNICEF/ICCIDD mUIC categories for classification of iodine nutrition as "adequate" and "above adequate" could be combined into a single "adequate" range based on Tg results showing no negative effect on the thyroid at the current "above adequate" range. Conclusions: A number of refinements to the current global recommendations in assessing iodine status were identified, including the importance of including PW and/or NPW in population-based assessments, and reconsideration of current mUIC criteria for the classification of optimal iodine nutrition in SAC.