RESEARCH OF THE SAFE DIETARY IODINE INTAKE IN ADULTS / 营养学报

ABSTRACT

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 2000?g 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 272.25?g/L,and the dietary iodine intake including iodinized salt was 346.24?g/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 ?g/d after 2 w.After 4 w the prevalence of subclinical hypothyroidism kept the same level at 500?g/d(15%),and increased at other iodine supplemented groups. The subclinical hypothyroidism prevalence at the 750-2000?g/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(500?g～2000?g) in a short time.It can lead to subclinical hypothyroidism in the subjects at 500?g /d doses.In iodine-sufficient area iodine supplemented dose was not appropriate to exceed 500?g/d.We suggested the UL of iodine below 900 ?g/d.