To explore the average requirement of total daily iodine intake in euthyroid women of childbearing age.
A 2-phase, double-blind, self-controlled iodine balance study was conducted in 25 euthyroid Chinese women for 4 weeks, recruited in Tianjin Medical University. Unified diet with different iodine content were provided usingduplicate portionmethod in two phases respectively; total iodine intake (including dietary iodine, water iodine, breath iodine) and total iodine excretion (from urine, feces and breath) were determined on 3 days of each week, 12 days and 300 samples in total. Establish the linear regression model between 24-h iodine intake and 24-h iodine excretion, the value of 24h iodine intake when it equals to 24h iodine excretion (i.e. zero iodine balance ), is the EAR of iodine intake.
The iodine intake in the 2 phases of the participants were 195.5±62.1µg/d and 563.2±90.2µg/d, respectively. Compared with the 1th phase, all participants responded with significant increases in 24h urinary iodine excretion (P<0.05) and 24h fecal iodine excretion (P<0.05) in the 2th period. 96.3% of a total 299 person-days (1 case missed) were in positive balance, while only 10 cases presented negative balance and all occurred in the 1th phase. The zero iodine balance' was reached, when 24h iodine intake was 80.2µg/d.
The average requirement of total daily iodine intake in euthyroid women of childbearing age was 80.21µg/d, thus a recommended iodine intake of 112.3µg/d was deduced and additional iodine supplement was proposed to maximize intra-thyroidal iodine stores before conception for the increasing demand during pregnancy.