青年人碘膳食参考摄入量研究

The physiological function of trace elements iodine is reflected by the role of thyroid hormones. Both iodine deficiency and excess can harm health. With a significant increase in thyroid disease, iodine excess has become a hot issue. With the relevant preliminary studies, we found that there may be "overkill" problem in current urinary iodine evaluation criteria proposed by WHO/UNICEF/ICCIDD. Based on a comprehensive related literatures analysis of more than 50 years of human iodine dietary reference intake and our previous iodine balance studies in young adult, we propose that there may be also "over standard" problem in the current RNI of iodine for adult. We innovatively propose "iodine overflow hypothesis". The hypothesis is, the body can fully and effectively absorb and use iodine, when required iodine is adequate to meet the thyroid hormone synthesis and the necessary storage in vivo, the remaining iodine will be excreted. According to this hypothesis of iodine metabolic balance test for young adult, iodine emissions will increase with the increase of iodine intake, when more than a certain threshold, then the increased intake of iodine will be "overflow" and excreted , This "spillover" should be the lower limit of iodine Dietary Reference Intakes for young adult. This application study will provide an important scientific basis for formulating a reasonable reference intake of iodine in adults, and has an important scientific value in preventing the risk of overdosing of iodine which may be caused by "excessive standards", and has an important practical value for guiding residents to "make up iodine accurately".

微量元素碘生理功能是通过甲状腺激素的作用来体现，碘缺乏和过量均可损害健康。随着甲状腺疾病显著增加，碘过量已成为关注的热点。课题组在相关前期研究中，发现由WHO等提出的现行尿碘评价标准可能存在“矫枉过正”问题。综合分析50多年来人体碘膳食参考摄入量相关文献及课题组进行的前期人体试验，认为目前成年人碘膳食参考摄入量可能存在“标准过高”问题，创新性提出“碘溢出说”，即人体可充分有效吸收利用碘，当满足合成甲状腺激素所需和必要体内储存后，剩余的碘都将排出体外。根据此科学假设进行青年人碘代谢平衡试验，碘排出量会随着碘摄入量的增加而增加，当超过某一阈值后，再增加的摄入碘也将“如数溢出”而排出体外，此“溢出域”应为青年人碘膳食参考摄入量的低限。本申请项目可为制定合理的成年人碘膳食参考摄入量提供重要科学依据，对防止由于“标准过高”可能产生的碘过量的风险和指导居民“科学精准补碘”都具有重要的科学和实际意义。

综合既往研究发现目前中国成人碘膳食参考摄入量可能存在“标准过高”问题，课题组遂提出了“碘溢出”科学假设。本研究在该指导下开展青年人群碘代谢平衡试验对人体碘生理需要量及膳食参考摄入量予以探索。研究经招募和严格筛选，分别纳入身体健康，BMI正常的青年男性38名，女性36名。依据试验方案，经2−4周适应和碘耗竭期后进入6个阶段的试验期，按照试验阶段呈递增地给予不同碘水平的试验膳食，采用膳食记录法称重、记录每人每日食物消耗量，收集每人每天产生的排泄物（24小时尿液、粪便）、称重和记录，运用电感耦合等离子体质谱法测定全部膳食与排泄物的碘含量，计算试验期每人每日碘膳食摄入量和碘排出量。以阶段1为参照，计算每人从阶段2至阶段6的碘膳食摄入增量与排泄增量，并应用多水平混合效应模型分析碘摄入增量与排出增量的函数关系。结果显示，试验期膳食碘摄入量男性从16.3μg/day增至134.0μg/day，摄入增量由11.8μg/day（阶段2）升至118.1μg/day（阶段6），排出增量从18.1μg/day升至99.8μg/day；女性从13.6μg/day增至133.0μg/day，摄入增量由21.1μg/day（阶段2）升至120.3μg/day（阶段6），排出增量由25.8μg/day增至105.4μg/day。根据碘代谢平衡的函数计算获得青年人碘生理需要量：男性48.0μg/day，女性52.2μg/day，考虑到研究对象生理因素及可能干扰对碘膳食参考摄入量估计，即换算为男性67.2μg/day（1.04μg/kg*day），女性73.1μg/day（1.4μg/kg*day）。本研究初步验证了所提出的“碘溢出”假说，不仅为修订中国居民膳食碘参考摄入量提供了直接的人群研究结果，还为探索中国成年人碘膳食参考摄入量及实施科学补碘提供了新的研究思路和重要理论参考。对防止因“标准过高”可能产生的碘过量风险，指导居民“科学精准补碘”具有重要的现实意义。

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