Study On Iodine Nutrition Survey Of Children In Low Water Iodine Area And Iodine Balance Experiment In Children

Objective: 1.To identify the iodine nutritional status of children in areas with no iodized salt supply and low water iodine,and assess the health risks to children exposed to mild iodine deficiency.2.To define the "zero" balance value for iodine-appropriate children,and provide data supporting the revision of the iodine reference intakes for children in China.3.To clarify the variations of commonly used iodine nutrition evaluation indicators and the sample size required to assess iodine nutrition based on the iodine balance experiment,and to explore new indicators for individual and population iodine nutrition evaluation.Method: 1.Iodine nutrition survey of children was carried out in the villages and towns with low water iodine and no iodized salt supply.Basic information,venous blood,water samples,dietary information,spot urine and two 24-hour(24-h)urine were collected and thyroid ultrasound was performed to comprehensively assess children’s thyroid function and iodine nutrition status.2.An iodine balance experiment was conducted in children.All food and water ingested by the subjects were measured by the weighing method,and 24-h urine and feces were collected.Iodine intake and excretion were assessed,and saliva samples were collected six times a day.3.The research method is the same as study 2.Results: 1.The percentages of children aged 7-10 years and 11-13 years below the recommended iodine intake in areas with low water iodine and no iodized salt supply were 62.3% and 73.2%,respectively.The inflection points of the relationship between thyroid stimulating hormone(TSH),free triiodothyronine(FT3),and free thyroxine(FT4)and iodine intake were 80.6μg/d,81.7μg/d,and 82.9μg/d,respectively.The risk of goiter was significantly higher in the iodine intake group of 91-120μg/d than that in the iodine intake group of 151-200μg/d(OR=2.9,95% CI:1.2,7.3).2.The 24-h urinary iodine excretion rate tends to increase with increasing iodine intake when the iodine intake is lower than 89.6μg/d,and decreases significantly with increasing iodine intake when the iodine intake is higher than 89.6μg/d.The corresponding "zero" balance values were 130μg/d,147μg/d,and 232μg/d for iodine intake of 145μg/d,191μg/d,and 495μg/d,respectively.The "zero" balance value shifted with increasing iodine intake.The "zero" balance values for children aged 7-10 years and 11-12 years with appropriate iodine intakes were 130μg/d and 140μg/d,respectively.3.The mean coefficient of variation(CV)of individual for dietary iodine intake(TII),24-hour urinary iodine concentration(24-h UIC),24-hour urinary iodine excretion(24-h UIE),and saliva iodine concentration(SIC)were 53.1%,47.7%,49.7%,and 42.7%,respectively.The mean CV of populations for TII,24-h UIC,24-h UIE,and SIC were66.7%,100%,72.5%,and 71.3%,respectively.The TII,24-h UIC,24-h UIE,and SIC sample sizes required for an individual’s iodine status evaluation were 25,14,20,and14 samples,respectively,at 95% CI and precision ±20%,and for a population’s iodine status evaluation were 34,108,49,and 45 samples,respectively.The correlation between SIC collected after dinner and TII of the day was the greatest(r=0.68,P<0.001)and was higher than the correlation between 24-h UIC and 24-h UIE and TII of the day(r=0.61,P<0.001;r=0.67,P<0.001).Conclusions:1.Children in areas with low water iodine and no iodized salt supply have a mild iodine deficiency.There is an increased risk of goiter in children with mild iodine deficiency.2.The use of the 92% 24-h urinary iodine excretion rate to extrapolate iodine intake is not uniform.The population iodine nutrition background needs to be considered.Combining with previous data,we obtained that iodine intake of 130-250μg/d is the safe iodine intake range for children aged 7-10 years,and iodine intake of 140-300μg/d is the safe iodine intake range for children aged 11-12 years.3.The CV of SIC was lower than that of 24-h UIE and 24-h UIC.The convenience and hygiene of disposable saliva collection are superior to that of 24-h urine collection.SIC is a good indicator of recent iodine nutrition status in individuals and populations.It is recommended to collect saliva samples after lunch(after 14:00).