| Aims: This study was to assess the iodine nutrition and thyroid function in children from areas with different iodine content in their drinking water, to explore the safety of different iodine intake levels in children and identify the upper safe intake level(UL) of iodine for children.Subjects and Methods: A cross-sectional study of children from areas with different water iodine contents in Shandong province. Dietary questionnaires and twice repeatedly sampling of 24-h urine and spot urine were applied to assess iodine intake.Thyroid volume was measured and total goiter rate (TGR) was calculated, while blood samplings were collected to measure thyroid function indicators.Results: This study enrolled 2224 children including 1100 boys and 1114 girls from four counties Ningjin, Lingxian, Gaotang and Dongchangfu. Children were 11 (10-12)years old, and the median iodine contents of drinking water from four counties were 30.5 (23.9-74.4) ?g/L, 112 (37.3-168) ?g/L,648 (515-753) ?g/L and 314 (184-385)?g/L, respectively. The median iodine content of water in this study was 181(67.2-402) ?g/L. In the first sampling, the median urinary iodine concentration (UIC)of spot urine and 24-h urine (24-h UIC) were 481 (218-818) ?g/L and 380 (203-646)?g/L, while the spot UIC and 24-h UIC were 417 (195-753) ?g/L and 397 (200-682)?g/L, respectively, indicating iodine status of children in this study was excessive. In addition, the iodine concentration of children from Gaotang was higher than other areas. The FT3, FT4, thyroid stimulating hormone (TSH), thyroglobulin (Tg) and Tvol of children were 5.8±0.7pmol/l, 16.4±2.1pmol/l, 2.9 (2.1,4.0) mIU/L,16.0 (9.8,26.1)?g/L and 4.37ml (3.33, 5.75) ml,respectively. The TGR was 9.7%. 237 (11.5%)children were diagnosed as subclinical hypothyroidism (SCH), besides, 5 children were hyperthyroidism and 2 children were subclinical hyperthyroidism while no hypothyroidism. The FT3 among children from four areas was not different, while TSH?Tvol and Tg of children from Gaotang were significantly higher than children from other three areas (P<0.0001). Besides, the TGR was 21.8% and incidence of SCH was 14.5%, significantly higher than other areas. 140 (6.8%) children were TPOAb while 43 (2.1%) were TGAb positive. The positive rate of TGAb was not significant different among four areas. TSH, Tvol and Tg were positively correlated with each other.The habitual iodine intake (Best linear unbiased predicator, BLUP) of children was 298 (186-437) ?g/d. TSH of children increased as the increase of iodine intake(r=0.11, P<0.0001),while the incidence of SCH was 11.2% in children with iodine intake of 200-300?g/d and increased accordingly. Using logistic regression and two-piecewise linear regression, a nonlinear association was observed between Tvols,TGR and iodine intake levels, with a threshold at an iodine intake level of 150?g/d.Tvol begin to increase when iodine of children >150?/d. After grouping with age,TGR exceeded 5% when iodine intake was 200-250?g/d in 7-10 year-old children and TGR exceeded 5% when iodine intake was 250-300?g/d in 11-14 year-old children. Similarly, a nonlinear association was observed between Tg, Tg>40 ?g/L and iodine intake levels, with a threshold at an iodine intake level of 120?g/d and 200?g/d, respectively. Adjusting by age, sex, height, weight, logistical regression analysis show that the risk of TGR significantly increased at iodine intake of 250-300?g/d in 7-10 year-old children and the risk of TGR increased at iodine intake of 300-400?/d in 11-14 year-old children, and the OR values was getting higher as iodine intake. However, there were no differences in the risk of SCH and Tg>40 ?g/L among different iodine intake groups (P>0.05).Conclusions: 1. Iodine status of children were excessive in areas with high iodine content in drinking water, UIC of children increases as water iodine level; 2. TSH,Tvol and Tg were significant higher in children from areas with high water iodine,and the incidences of SCH and TGR were also higher than other areas; 3.Tvol and Tg of children increased as iodine intake, while the correlation between TSH and iodine intake was not significant, as the risks of SCH and Tg>40 ?g/L were also not different among different iodine intake groups when adjusting by other factors; 4.Based on the above results, we recommend the UL of iodine for 7-10 year-old children is 250?g/d and the UL of iodine for 11-14-year-old children was 300?g/d. |
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