关于成人碘安全摄入量的探讨

目的探讨成人碘的安全摄入量。方法选择甲状腺功能正常的(22.54±2.65岁)健康志愿者。随机分为7组,各组每人每日分别服用500,750,1000,1250,1500,1750,2000μg的碘剂,为期4w。于实验前、实验第2w以及实验结束时分别采集志愿者空腹血、晨尿。用化学发光免疫分析法测定血清FT4、灵敏促甲状腺激素(sTSH),定量放免法测定甲状腺过氧化物酶抗体(thyroid peroxidase antibody,TPOAb)、甲状腺球蛋白抗体(thyroglobulin antibody,TGAb)浓度,用砷铈氧化还原法测定尿碘水平。对被调查者进行为期7 d的膳食调查。采集天津市市售食物、饮用水样品,以及食盐样品,测定其碘含量。结果补碘前人群碘摄入水平充足,尿碘中位数为272.25μg/L,被调查者膳食碘摄入的平均值(含碘盐)为346.24μg/d。与补充碘剂前相比,补碘后各组人群尿碘水平明显增加;血清FT4在正常值范围内下降;各组人群在补充碘剂2 w后血清sTSH明显上升,与补碘前相比增加近1倍多,至4 w后增加近2倍。各剂量组间相比血清sTSH变化幅度基本一致。正常人群补充500～2000μg碘剂2 w后出现了亚临床甲状腺功能减退,各剂量组的发病率在15.00%~47.37%之间。试验结束时未见临床甲减患者。结论正常人群补充500μg/d碘即可引起亚临床甲状腺功能减退。因此,对于生活在碘营养充足地区的人群每日碘的补充剂量不宜超过500μg,结合每日膳食碘的摄入量,我们建议碘的可耐受的最高摄入量(UL)的上限值应低于900μg。

RESEARCH OF THE SAFE DIETARY IODINE INTAKE IN ADULTS

Objective To explore the safety of iodine intake in adults.Method Euthyroid healthy volunteers aged 18 to 24 years(22.54±2.65y)were adopted and divided into 7 groups randomly.Each group was assigned to receive 500,750,1000,1250,1500,and 2000μg iodide oral doses daily for 4 w.Blood and urine samples during morning fast were obtained on weeks 0,2 and 4.We used chemiluminescence immunoassay(CLIA) to measure sTSH,FT4 and immunoradiometric assay(IRMA) to measure TPOAb and TGAb.Urinary iodine was evaluated.The dietary survey was done by recording method to collect food consumption data for 7 d.We also measured the iodine amount in drinking water,food and iodinized salt.Results All the volunteers were in adequate iodine levels.The median urinary iodine was 272.25μg/L,and the dietary iodine intake including iodinized salt was 346.24μg/d.We found all the iodide supplemented groups responded in the same way with a significant rise in urinary iodide excretion and in serum sTSH levels,with a small decline in serum FT4 concentration at normal range.After 2 w the serum sTSH levels in the iodide supplemented groups increased nearly more than double,and nearly two fold after 4 w.The subclinical hypothyroidism appeared at 500～2000 μg/d after 2 w.After 4 w the prevalence of subclinical hypothyroidism kept the same level at 500μg/d(15%),and increased at other iodine supplemented groups. The subclinical hypothyroidism prevalence at the 750-2000μg/d doses was at the range of 28.00%～47.37%.No clinical hypothyroidism was observed among the people during iodide administration.Conclusion The dysfunction of thyroid in normal population was mainly subclinical hypothyroidism with an exposure to a high dose iodine intake(500μg～2000μg) in a short time.It can lead to subclinical hypothyroidism in the subjects at 500μg /d doses.In iodine-sufficient area iodine supplemented dose was not appropriate to exceed 500μg/d.We suggested the UL of iodine below 900 μg/d.