Prevalence of thyroid dysfunction with adequate and excessive iodine intake in Hebei Province, People’s Republic of China

Abstract

Objective: To explore (i) the prevalence of thyroid dysfunction in populations with adequate and excessive iodine intakes and (ii) the effect of iodine exposure on the prevalence of thyroid dysfunction. Design: Cross-sectional study was conducted in Hebei in 2010. The population was classified as having adequate or excessive iodine intake according to the iodine concentration in drinking water. Demographic information was collected by questionnaire. Levels of serum thyroid hormones, thyroid autoantibodies and iodine in drinking water and urine were measured. Setting: Villages with adequate or excessive drinking water iodine in Hebei Province, People's Republic of China. Subjects: A total of 854 men and women aged 20-50 years who had lived in the surveyed areas for over 5 years, including 348 from the adequate iodine area (AIA) and 506 from the excessive iodine area (EIA). Results: Median urinary iodine concentration was 185 μg/l in AIA and 1152 μg/l in EIA. The prevalence of thyroid dysfunction in AIA was 10·3 %, which included 1·1 % with hypothyroidism and 8·1 % with subclinical hypothyroidism; and 20·6 % in EIA, which included 3·6 % with hypothyroidism and 13·6 % with subclinical hypothyroidism. The positive rates of thyroglobulin antibody were 16·1 % in AIA and 11·9 % in EIA; the positive rates of thyroperoxidase antibody were 20·7 % in AIA and 16·4 % in EIA. Conclusions: Excessive iodine intake may lead to increased prevalence of biochemical thyroid dysfunction, especially biochemical hypothyroidism. This is not related to an increase in prevalence of thyroid antibodies. Women are more susceptible to iodine excess.

Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies

“…Since only one of these reported biomarker values [36], Table 4 tabulates results for thyroid diseases only. The paper by Szabolcs et al .…”

“…The cause was not assessed in one paper because of an adequate median UIC [40]. Four studies compared high and low iodine status populations [35, 36, 37, 41], three papers described one population with a median or mean UIC of the total population of over 300 μg/L [38, 39, 42], and one paper reported that median UIC was adequate but assessed categories of UIC over 300 μg/L [41]. Regarding study quality, three papers used a regression model [35, 40, 42], of which two used models for some of the outcomes [35, 42].…”

“…[36], serum FT4, FT3 and TSH values were compared between two areas. No significant differences were found in FT4 and FT3, while two values of TSH were significantly different.…”

“…Among papers in adults, only one showed results for biomarkers of thyroid hormones (footnote of Table 4), namely a significant elevation in TSH in the excess group [36]. In children, nine papers [43–45, 50, 59, 61–64] evaluated biomarkers, of which five also assessed thyroid diseases (Table 6).…”

Risks of excess iodine intake in Ghana: current situation, challenges, and lessons for the future

“…However, permanent metabolic effects of excess iodine intake could occur if the iodine source is not detected and discontinued . Excess iodine intake has been reported in China, and among African refugees in Sudan, Algeria, and Somalia, mainly associated with drinking water and the use of iodized salt …”