Epidemiological survey on the relationship between different iodine intakes and the prevalence of hyperthyroidism

Abstract

Objective: To investigate the effect of different levels of iodine intake on the prevalence of hyperthyroidism and the impact of universal salt iodization on the incidence of hyperthyroidism. Design: A comparative cross-sectional and longitudinal survey was conducted in three areas with borderline iodine deficiency, mild iodine excess (previously mild iodine deficiency) and severe iodine excess. Universal salt iodization had been introduced 3 years previously except in the area with borderline iodine deficiency. Methods: In total 16 287 inhabitants from three areas answered a questionnaire concerning the history of thyroid disease. Among them 3761 unselected subjects received further investigations including thyroid function, thyroid autoantibodies, thyroid ultrasonography and urinary iodine excretion. Results: Among areas with median urinary iodine excretion of 103 mg/l, 375 mg/l and 615 mg/l ðP , 0:05Þ; the prevalence of hyperthyroidism did not differ significantly (1.6%, 2% and 1.2%). The prevalence of subclinical hyperthyroidism was higher in areas with borderline iodine deficiency and mild iodine excess than in the area with severe excess iodine intake (3.7%, 3.9% and 1.1%, P , 0:001). The prevalence of Graves' disease and its proportion in hyperthyroidism did not differ among areas. The incidence of hyperthyroidism did not significantly increase after the introduction of universal salt iodization. Conclusion: Different iodine intakes under a certain range do not affect the prevalence and type of hyperthyroidism. Subclinical hyperthyroidism is more prevalent in the iodine deficient area than in the severe iodine excessive area. In the area with mild iodine deficiency, the introduction of universal salt iodization may not be accompanied by an increased incidence of hyperthyroidism.

More than adequate iodine intake may increase subclinical hypothyroidism and autoimmune thyroiditis: a cross-sectional study based on two Chinese communities with different iodine intake levels

“…GD was the main cause of overt hyperthyroidism in both the communities. Our 5-year follow-up study also reported that there was no difference in either the prevalence or the incidence of overt hyperthyroidism in areas with MUI of 84 mg/l (a mildly deficient iodine intake area), 243 mg/l (a more than adequate iodine intake area), and 651 mg/l (an excessive iodine intake area) (57,58). Thus, from our epidemiological studies, we infer that excess chronic iodine would not increase the prevalence of overt hyperthyroidism.…”

Chronic iodine excess does not increase the incidence of hyperthyroidism: a prospective community-based epidemiological survey in China

“…It has been well documented that there may be a transient increase in the incidence of hyperthyroidism due to IIH after iodine supplementation to iodine-deficient populations, but eventually the incidence of hyperthyroidism would fall to a lower level with long-term stable iodine intake (6, 7). In our original survey, the prevalence of hyperthyroidism was not remarkably different among the three communities and the data acquired from a retrospective investigation also showed no significant increase after iodine supplementation (10). In the present paper, there was no statistical difference in the incidence of hyperthyroidism between Panshan and Zhangwu communities.…”

“…We have previously reported in a cross-sectional survey that the prevalence of overt hyperthyroidism was not remarkably different among three communities with different iodine nutritional status: borderline iodine deficiency, more than adequate iodine intake and iodine excess (10). The study was also designed prospectively to acquire the incidence of overt as well as subclinical hyperthyroidism of the three populations, and the final results offered by the present paper may provide information about the relationship between different levels of iodine intake and epidemiological pattern of hyperthyroidism.…”

Safe Range of Iodine Intake Levels: A Comparative Study of Thyroid Diseases in Three Women Population Cohorts with Slightly Different Iodine Intake Levels

“…As previously described [6], serum thyrotropin (TSH), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), and thyroglobulin (Tg) were measured in all participants. Free thyroxine (FT 4 ) and free tri-iodothyronine (FT 3 ) were determined in those subjects with abnormal TSH (chemiluminescent immunoassay for TSH, TPOAb, TgAb, Tg, FT 4 , and FT 3 , Diagnostic Products Corporation, Los Angeles, CA, USA).…”