碘过量对儿童健康的危害及其安全摄入量的研究

Iodine deficiency diseases have been successfully controlled since the implementation of salt iodization, however more and more attention was drown to the hazard caused by excessive iodine intake, and the safety of salt iodization has become the public concern issue. Confirming the tolerable upper intake level of iodine for different population is the key of preventing excessive iodine intake and scientifically persisting in iodine supplementation, which is also the current public health problem need to urgently solved. With early investigation and human experiment, we have successfully established the tolerable upper safe level of iodine for adult, simultaneously we found the upper safe level of iodine of 800μg/d for children was pretty high during the epidemiological study in children, which need to be further studied. Thus, our group will carry out a cross-sectional study on children who live in high water iodine areas, adopting 24h-urinary iodine to precisely evaluate iodine intake of children exposed to different levels of water iodine, and detecting TSH、T3 、T4 、 TPOAb、TGAb to identify the upper safe level of iodine for children in our country and explore the effects on health of children with long-term high iodine exposure. The results of this study will provide data for revising Chinese DRIs and will be meaningful for preventing excessive iodine intake and assuring the sustained and proper implementation of salt iodization in future.

随着食盐加碘政策实施成功地控制了碘缺乏病，人们开始重视碘过量对健康的危害，食盐加碘的安全性也引起社会关注。确定碘可耐受最高摄入量(tolerable upper intake level, UL)是防止碘过量摄入、坚持科学补碘的关键，亦是当前亟待解决的公共卫生问题。经过前期调查和实验，我们已成功制定成人碘安全摄入量，同时在儿童的流行病学调查中发现，目前我国规定的儿童碘安全上限值800μg/d过高，亟需开展研究制定适合我国儿童的碘UL。因此，本课题组拟对高水碘地区常住儿童进行横断面调查，采用24h尿碘精确评定不同水碘暴露下儿童碘摄入量，并对儿童的TSH、T3、T4、TPOAb、TGAb等与碘过量相关的敏感指标进行检测，明确我国儿童的碘安全摄入水平，探讨长期高碘暴露对儿童健康的影响。研究结果将为修订人群碘膳食参考摄入量(DRIs)提供依据，对高碘危害的防治及食盐补碘科学长久地实施具有重要意义。

本次研究共调查了2975名儿童，数据分析纳入了2224名儿童，包括1100名（49.5%）男孩以及1114（50.5%）名女孩，水碘中位数为181 (67.2-402) μg/l。在一个月内分别对儿童进行了两次一次性随机尿和24-h尿样的采集，第一次采样的随机尿碘浓度为481 (218-818) μg/l，24-h尿碘浓度为380 (203-646) μg/l，第二次采样的的随机尿碘浓度为417 (195-753) μg/l，24-h尿碘浓度为397 (200-682) μg/l，两次尿碘浓度均显示调查儿童的碘营养过剩。儿童的FT3水平为5.8±0.7pmol/l，FT4水平为16.4±2.1pmol/l，TSH水平为2.9（2.1, 4.0）mIU/L以及Tg浓度为16.0（9.8, 26.1）μg/L。在所有调查儿童中发现，亚临床甲状腺功能减退（亚甲减，Subclinical hypothyroidism, SCH）儿童有237例（11.5%），且男孩与女孩之间SCH发病率未见统计学差异。儿童甲状腺体积（Tvol）的大小为4.37ml (3.33, 5.75) ml，甲状腺肿大率（TGR）为9.7%。男孩的Tvol略大于女孩 (P=0.035)，但甲状腺肿大率（TGR）男女之间没有差异 (P=0.99)。儿童的估算碘摄入量为298 (186-437) μg/d，碘摄入量与TSH之间呈正相关关系（r=0.11, P<0.0001），在摄入量200-300μg/d，儿童亚甲减的发病率超过了10%，儿童的Tvol和TGR随着碘摄入量的升高而增大，当碘摄入量在250-300μg/d组别时，TGR超过5%，此外阈值效应模型分析可知150μg/d为转折点，当碘摄入量大于150μg/d时，Tvol和TGR随着儿童的碘摄入量的升高而升高。儿童Tg与碘摄入量之间存在曲线关系，经过年龄、性别、身高和体重的校正，阈值效应模型分析可知120μg/d为转折点，当碘摄入量大于120μg/d时，Tg随着碘摄入量增高有升高的风险，儿童摄入量大于200μg/d时，Tg>40 μg/L的风险随着摄入量的增加而增加。综上，儿童的碘安全摄入量上限值在200-300μg/d范围之内。