Chinese Female Adults Need More Iodine Intake Based on ‘Overflow Theory’

Abstract

Background: In China, there is a dearth of data on the iodine balance study for adults. Especially, due to the special physiological cycle, the research of female iodine balance is insufficient or lasts for a short time. In the present study, we spent more than two months to explore the basal iodine requirement based on healthy Chinese female adults and a new ‘iodine overflow’ theory was proposed for the study of iodine balance. Methods: A total of 36 Chinese healthy female adults (age 20.67 ± 1.10 years) were recruited for this study, which included 40 days low iodine depletion period and 6 stages of 30 days supplementation study. Uniform diets with different iodine content were provided, in which non-iodized salt and pure water were provided in all the meals and the content of iodine in the diet was regulated by accurately weighing dairy products with measured iodine content. The total iodine intake from food was collected using weighing and duplicate portion method and the total iodine excretion through 24-hour urine and staged faeces were completely gathered and monitored. The iodine content in diet, urine and feces were measured by ICP-MS. The iodine intake and excretion were calculated and a mixed effects models model was set up between incremental iodine intake and incremental iodine excretion based on the ‘iodine overflow’ theory. Findings: At the start of experiment, the 24h UIC was 233.31±122.47μg/L, which meant an iodine overnutrition for the majority of subjects. The iodine intake and excretion were 13.64μg/day and 48.58μg/day at the end of 1st stage. The incremental iodine intakes (Δ iodine intake) was 21.05, 39.64, 60.85, 88.16, 120.25μg/day and the incremental iodine excretion (Δ iodine excretion) was 25.75, 37.03, 54.67, 77.59, 105.43μg/day for the supplementation stages. According to the ‘iodine overflow’ hypothesis, the zero iodine balance (Δ iodine intake = Δ iodine excretion) derived from a mixed effect model indicated a mean iodine intake of 52.24μg/d(1.00μg/d•kg). The RNI for iodine to healthy Chinese female adult was 73.1μg/d(1.39μg/d•kg). Interpretation: Our findings indicate that basal iodine requirement may be much less than the current iodine intake recommendation. A daily iodine intake of 52.24μg/d may meet the basal iodine requirement for healthy Chinese female and Chinese women may need more than 20% iodine intake than men based on the ‘iodine overflow’ hypothesis. The ‘iodine overflow’ theory could provide a new idea for iodine balance research and the further studies should be needed for the iodine intake recommendation. Trial Registration: The trial was registered at the Chinese Clinical Trial Registry (No:ChiCTR1800016184). Funding: National Natural Science Foundation of China and Sanming Project of Medicine in Shenzhen. Declaration of Interest: The authors declare that they have no conflict of interest. Ethical Approval: This study was approved by the Ethical Committee of the National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention.