A dose-response crossover iodine balance study to determine iodine requirements in early infancy

Abstract

Background: Optimal iodine intake during infancy is critical for brain development, but no estimated average requirement (EAR) is available for this age group. Objective: We measured daily iodine intake, excretion, and retention over a range of iodine intakes in early infancy to determine the minimum daily intake required to achieve iodine balance. Design: In a dose-response crossover study, we randomly assigned healthy infants (n = 11; mean 6 SD age 13 6 3 wk) to sequentially consume over 33 d 3 infant formula milks (IFMs) containing 10.5, 19.3, and 38.5 mg I/100 kcal, respectively. Each IFM was consumed for 11 d, consisting of a 6-d run-in period followed by a 4-d balance period and 1 run-out day. Results: Iodine intake (mean 6 SD: 54.6 6 8.1, 142.3 6 23.1, and 268.4 6 32.6 mg/d), excretion (55.9 6 8.6, 121.9 6 21.7, and 228.7 6 39.3 mg/d), and retention (21.6 6 8.3, 20.6 6 21.6, and 39.8 6 34.3 mg/d) differed among the low, middle, and high iodine IFM groups (P , 0.001 for all). There was a linear relation between daily iodine intake and both daily iodine excretion and daily iodine retention. Zero balance (iodine intake = iodine excretion, iodine retention = 0 mg/d) was achieved at a daily iodine intake of 70 mg (95% CI: 60, 80 mg). Conclusion: Our data indicate the iodine requirement in 2- To 5-moold infants is 70 mg/d. Adding an allowance for accumulation of thyroidal iodine stores would produce an EAR of 72 mg and a recommended dietary allowance of 80 mg. This trial was registered at clinicaltrials.gov as NCT02045784. Am J Clin Nutr 2016;104:620-8.