Abstract: ObjectiveTo observe the effct of different levels of iodine intake on iodine metabolism and thyroid function as well as its safety in rats.MethodsWistar rats were randomly divided into six groups:low iodine(LI),normal iodine(NI) and 4 excessive iodine(HI,including 5,10,50,100 folds of normal iodine)based on the iodine levels contained in their diet.3, 6 and 12 months later,the iodine metabolism was through the levels of urinary iodine and iodine contents in thyroid gland.The thyroid function was determined by serum levels of TT₄,TT₃,FT₃,FT₄ and contents of T₄,T₃ in thyroid tissues.ResultsUrinary iodine,tissue iodine,thyroid hormones in serum and thyroid tissues in LI group were considerably lower than NI group,which indicated the status of severe hypothyroidism occurred in LI rats.HI groups showed statistically high urinary iodine paralleling to iodine intake.However,iodine contents in thyroid gland of HI groups was only within 2 folds of that in NI group.The tendency of hypothyroidism was demonstrated in HI groups with increase of iodine intake as indicated by the decreasing of thyroid hormones in serum and thyroid tissues.ConclusionLong term iodine deficiency and iodine excess can cause hypothyroidism in rats,but more obviously in iodine deficiency group.Wistar rats showed stronger tolerance to excessive iodine intake through the adaptation mechanism,and the safety of daily intake of KIO₃ was confirmed.