| Objective: 1. To explore the appropriate recommended nutrient intake of iodine in euthyroid Chinese women of childbearing age through the iodine balance study under different levels of iodine intake, and related aspects about experiment methods are discussed. 2. To explore the effects of different iodine intake levels on each part of the iodine excretion.Methods: A 4-wk, double-blind, self-controlled study was conducted in 25 euthyroid Chinese bearing-age females, who were recruited in Tianjin Medical University, through urine iodine concentration and thyroid function screening. Unified diet with different iodine content were provided in two different periods respectively, monitor and determine the quantities of dietary iodine, water iodine, urinary iodine, fecal iodine and breath iodine on three days of each week, 12 days and 300 samples in total. Establish the linear regression model between the 24-h iodine intake and the 24-h iodine excretion. The value of the 24 h iodine intake when it equals to the 24 h iodine excretion, is the EAR of iodine intake, then we can calculate the RNI of iodine intake in the Chinese women of childbearing age.Results: 1. The average iodine intake was 195.51?g/d in the first phase, including dietary iodine 173.45?g/d?water iodine 21.39?g/d and respiratory iodine 0.70?g/d; In the second phase the average iodine intake was 563.24?g/d, among which, dietary iodine intake?water iodine intake and breath iodine intake were 543.46?g/d?19.06?g/d and 0.70?g/d; The iodine intake in the second stage was higher than that in the first stage(P<0.05). 2. The contribution of dietary?water and breath to iodine intake, expressed as a percentage of total iodine intake, were 88.72%?10.94%?0.36% respectively in the first period; Diet with iodized salt was prepared in the second period, the contribution of dietary was increased to about 96.50%, the total contribution of drinking water and breath was about 3.50%. 3. There was a total of 42 cases did not meet the iodine RNI standard recommended by Chinese nutrition society in the first phase, accounting for 18.67% of the total; In the second stage, iodine intake of all the volunteers reached the iodine RNI standard 120?g/d. 4. The daily urine output of the volunteers averaged 1.34±0.50 L, which was significantly positive correlated with the daily water consumption(r=0.76, P=0.000)and no statistical difference was observed in the two periods; The median of UIC and UIE were 75.90?g /L and 97.20?g /d respectively, in the first phase, in the second phase, the median of UIC and UIE increased to 187.13?g/L and 216.37?g/d, respectively(P<0.05); Spearman correlation analysis was carried out on the two variables 24h-UIE and 24h-TI, significant positive correlation was observed(r=0.71, P<0.05). 5. The proportions with a UIC < 100?g/L(the cutoff for iodine in-sufficiency) in the first phase and the second phase were 73.78% and 8.00%, respectively, There was statistically significant difference of UIC distribution between different periods(P<0.05). 6. Fecal iodine excretion was also associated with the total iodine intake(r=0.44, P<0.05); In the first stage, the median of fecal iodine excretion was 12.78?g/d, with the increase of iodine intake, the fecal iodine excretion increased to 32.08?g/d(P<0.05). 7. 24h-TE was significantly positive correlated with 24h-TI(r=0.82, P<0.05); Regression analysis was carried out on the two variables, identified an obligatory excretion of I(i.e. an excretion of iodine independent of intake) amounting to 52.86?g/d, and it was also shown that the fraction of intake excreted was approximately 0.34; The 24h-TE in the second period was significant higher than that in the first period(P<0.05); 8. With iodine intake increasing, the distribution of each part of iodine discharge was basically constant, urinary iodine accounted for 87%~88%, while fecal iodine accounted for 12%~13% and expiratory iodine excretion below 0.5%. 9. 96.33% of a total 300 person-days were in positive balance, while only 10 cases presented negative balance and all occurred in the first phase. 10. When the 24h-TI reached 80.21?g/d, the ‘zero iodine balance' was reached.Conclusions: 1.We suggest that the estimated average requirement(EAR) and recommended nutrient intakes(RNI) of iodine in euthyroid reproductive age women is 80?g/d and 115?g/d, respectively. 2. With the iodine intake increasing, iodine discharge in urine and feces increased accordingly, but the proportion of each branch was basically constant; the proportion of breath iodine is so small that can be ignored. |
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