| Objective: The current reference standard of recommended nutrient intake(RNI)of iodine for toddlers in China was based on the results of foreign iodine balance tests in1970 s.There were some problems in the foreign research at that time,and the standard of iodine requirements for toddlers used in China may be miscalculated.Therefore,this study was based on the iodine metabolism of Chinese toddlers by the iodine balance experiment to explore the reference value of dietary iodine intake of iodine EAR level of toddlers,and to deduce the reference value of dietary iodine intake of RNI level.To provide data reference for protecting the appropriate iodine level of toddlers.Methods: Based on the geographical advantages of natural areas with high water iodine in China,this study selected kindergartens in Xizhaizhuang Township,Jinghai County,Tianjin,through baseline survey,urinary iodine assessment and growth and development assessment.A total of 26 healthy toddlers aged 2～3 years old were included.Based on the local characteristics of high water iodine,this study adopted a two-dose cross experimental design,which was carried out in two stages.The iodine intake levels of toddlers in the two stages were 90～129 μg/d(the first dose level)and130～180 μg/d(the second dose level),respectively.The cycle of each stage is 15 days,that is,10 days of elution and 5 days of iodine balance,with a total of 30 days(15days×2).During the period of iodine balance(5 days×2),the food of children for 10 days was collected by double meal method,and 24 h urine,24 h feces and all drinking water samples were collected.Determination of iodine in food,water,urine and feces by ICP-MS.Based on the iodine balance data,the regression curve and regression equation were established.When the iodine intake reached zero iodine balance,the reference value of iodine intake at EAR level was calculated,and then the reference value of iodine intake at RNI level was calculated.Results: 1.The growth and development of toddlers were good.Except for HAZ(P<0.05),the difference between boys and girls was statistically significant(P>0.05).2.The total iodine intake of children at the first dose level was 139.83±19.48 μg/d,of which food iodine intake was 114.86±22.52 μg/d,and water iodine intake was24.97±9.37 μg/d,accounting for 82.14% and 17.86% of the total iodine intake,respectively.in which food iodine intake was 123.86±29.46 μg/d and water iodine intake was 82.81±18.70 μg/d,accounting for 59.93% and 40.07%,respectively.There was no significant difference in the food iodine intake between the two dose levels of toddlers.The intake of water iodine and total iodine at the second dose level was higher than that at the first dose level(t=-31.529,P<0.001;t=-22.701,P<0.001).3.The average of iodine loss in sweat was 7.17μg/d.The total iodine excretion at the first dose level was 127.60±19.67 μg/d,the median of 24h-UIE was 109.78(95.09,121.24)μg/d,the median of fecal iodine excretion was 10.91(8.77,13.49)μg/d.Urinary iodine excretion and fecal iodine excretion accounted for 85.71% and 8.84%of the total iodine excretion,respectively.The total iodine excretion at the second dose level was 178.25±32.37 μg/d,the median of 24h-UIE was 150.88(130.78,180.78)μg/d,the median of fecal iodine excretion was 15.54(9.87,19.64)μg/d,accounting for 86.72% and 8.71% of the total iodine excretion,respectively.The total iodine excretion,24h-UIE and fecal iodine excretion at the second dose level were higher than those at the first dose level(t=-15.244,P<0.001;Z=5.023,P<0.001;Z=1.983,P<0.05).4.There was a positive correlation between total iodine intake and total iodine excretion.With the increase of total iodine intake,total iodine excretion,24h-UIE and fecal iodine excretion increased(r=0.869,P<0.001;r=0.833,P<0.001;r=0.388,P<0.001).The excretion of 24h-UIE and fecal iodine accounted for 86.21%and 8.78% of the total iodine excretion respectively.The ratio of the urinary iodine excretion and fecal iodine excretion in the total iodine discharge was relatively stable.5.According to the daily total iodine intake and iodine balance value,a regression curve fitting was performed to obtain a regression equation: y=0.213x-16.634,which the reference values of EAR and RNI odine intake of toddlers were calculated to be78.09 μg/d and 109.33 μg/d.Conclusions: 1.The characteristics of iodine metabolism of toddlers show that: with the increase of iodine intake,the excretion of urinary iodine and fecal iodine also increases.When the iodine status of toddlers are sufficient,the ratio of urinary iodine excretion and fecal iodine excretion to total iodine intake and total iodine excretion ares relatively stable.2.Under the current iodine nutrition status,the reference valuesof iodine intake of EAR and RNI of toddlers are 78.09 μg/d and 109.33 μg/d,respectively,which are higher than the current standard of iodine requirement of toddlers in China. |
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