| Objective1.To determine the effect of iodine excess on thyroid function and autoimmune thyroid function by the survey of the iodine nutritional status and thyroid function of adults, children, pregnant women and newborn.2.To explore the safety iodine intake of adult and provide data reference for iodine UL.Method1.According to the inclusion criteria adults, children, pregnant women and newborns were selected from excessive iodine intake area and sufficient iodine intake area. Morning urine and blood samples were obtained from all the subjects. Serum was stored at-80℃until assayed. Water and salt samples were collected to determine the iodine content.2.95healthy volunteers (man55, woman40) were divided into5groups with varying iodine supplement doses ranging from0to400μg for4weeks. Fasting blood and urine samples were obtained in the morning on weeks0,2, and4, and the blood samples were stored at-80℃until they were analyzed. Thyroid ultrasounds utilizing a7.5MHz/40mm probe were performed by trained specialists. A part of subjects were followed up at third month and ninth month after iodine withdrawal. A seven consecutive24-hour dietary recall was used to record food they consumed for all subjects.Drinking water and salt samples were collected to determine the iodine content. Serum levels of free thyroxine (FT4), free triiodothyronine (FT3), and sensitive thyroid stimulating hormone (sTSH) were measured in all subjects with automated chemiluminescent immunoassay, the diagnostic kits from the Bayer Company. Serum levels of Thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TGAb) were measured with RIA. Urinary iodine and water iodine content were determined with the use of the colorimetric coercion-arsenious acid ash method. Salt iodine was determined with Direct titration; salt in food with Electric potential titration.Results1. The median urinary iodine of adults, children and pregnant women in excessive iodine areas were higher than the corresponding people in adequate iodine areas.(1152.01vsl85.20μg/L;1034.06vs120.95μg/L;1240.70vs217.06μg/L; P<0.05).2.The prevalence of thyroid diseases among the adults, children and pregnant women in iodine excess area were higher than the corresponding population iodine adequate areas (20.6%vs10.3%;11.9%vsl.3%;22.9%vs2.3%; P<0.05) Subclinical hypothyroidism was the main form of thyroid diseases among adults, children and pregnant women in excessive iodine areas(13.6%,6.5%,20%). The rate of sTSH>10μIU/ml (21%) and>20μIU/ml rate (7.6%) of neonate in excessive iodine areas were higher than the corresponding people in adequate iodine areas (1.1%,1.1%)(P <0.05).3. In addition to TGAb and TPOAb positive rate of children in excessive iodine areas were higher than iodine adequate regions (P<0.05), there were no differences in positive rate of TPOAb and TGAb of adults, pregnant women and newborns between the two areas. However, female adults and children in the thyroid antibodies positive rate were higher than in men(P<0.05).4. The serum sTSH concentration of adults and children with normal thyroid function in excessive iodine areas was higher than the corresponding people in adequate iodine areas(P<0.05).5.In the two areas the positive thyroid autoimmune antibodies rate of adults and children with thyroid disease were higher than the corresponding people with normal thyroid function(P<0.05). In excessive iodine areas the positive thyroid autoimmune antibodies rate of the children with subclinical hypothyroidism increased significantly than those who with normal thyroid function (TPOAb:25%vs5.2%; TGAb:20.8%vs5.2%)(P<0.05), and the serum TSH concentration of children with positive thyroid autoimmune antibodies was higher than children with negative thyroid autoimmune antibodies. In adequate iodine areas the positive thyroid autoimmune antibodies rate of adults with subclinical hypothyroidism was higher than the corresponding people in excessive iodine areas (TPOAb:57.1%vs15.4%; TGAb:42.9%vs12.8%)(P <0.05).6.The serum sTSH concentration of pregnant women with positive TGAb in excessive iodine areas was higher than the corresponding people in adequate iodine areas (3.96μIU/ml vs1.10μIU/ml)(P<0.05).7.In the two areas the serum sTSH concentration showed positive correlation between the pregnant women and neonate(r=0.278, P=0.000; r=0.202, P=0.008), thyroid autoimmune antibodies showed the same change correlation between the pregnant women and neonate.8. In excessive iodine areas the rate of serum sTSH>10μIU/ml of pregnant women with subclinical hypothyroidism was higher than the corresponding people in adequate iodine areas (P<0.05), thyroid autoimmune antibodies of pregnant women with subclinical hypothyroidism had increased tendency, but no significant difference (P>0.05).9. The serum sTSH concentration of neonate whose mother with positive thyroid antibodies was higher than the corresponding people in adequate iodine areas (TPOAb:7.53μIU/mlvs5.09μIU/ml;TGAb:8.38μIU/mlvs5.86μIU/ml)(P<0.05).10.The re was a increase in FT4, FT3and sTSH concentrations but serum FT4, FT3remained within normal range. One person displayed subclinical hypothyroidism in group400μg and300μg at the4th week (5.3%,5.3%). One additional subject in group300μg had subclinical hypothyroidism at week2, but it disappeared at the end of the trial. After9month, the patient’s sTSH in group400μg/d decreased to critical value.11. TGAb and TPOAb had no significant change during iodine asministration.Conclusions1. Iodine excess increased the risk of thyroid diseases; the subclinical hypothyroidism was most obvious. In excessive iodine areas the main reason of subclinical hypothyroidism were the combined effects of high iodine and thyroid autoimmunity injury, however, in adequate areas thyroid autoimmunity damage may led to the subclinical hypothyroidism.2. The thyroid autoimmunity increased among the people with long-term high iodine exposure.It was greater effect of neonate whose mother with positive thyroid antibodies than the corresponding people in adequate iodine areas.3. Long-term excessive iodine intake of adults and children with normal thyroid function led to high sTSH concentration, and enhanced thyroid autoimmunity.4. Women showed more apparent in thyroid autoimmunity injury than men.5.There was a closed relation of thyroid autoimmunity between pregnant women and newborns, thyroid function of newborns was impacted directly by mothers.6. People with normal thyroid function appeared subclinical hypothyroidism with short-term (1month) excessive iodine intake, and the people returned to be normal after withdraw iodine supplement.7. For95%people the daily intake should not exceed700p,g/day. |
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