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

Teng, Xiaochun; Shi, Xiaoguang; Shan, Zhongyan; Jin, Ying; Guan, Haixia; Li, Yushu; Yang, Fan; Wang, Weibo; Tong, Yajie; Wang, Teng

doi:10.1007/s12011-007-8036-0

Cited by 18 publications

(11 citation statements)

References 16 publications

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“…A number of mechanisms may explain our findings, but the results may suggest that the iodine intake level of a population is an important determinant of the incidence of hypothyroidism, and consequently the treatment intensity of this disease. These results support earlier studies both in Denmark [19] and in other countries [20].…”

Section: Discussionsupporting

confidence: 93%

Doubling in the use of thyroid hormone replacement therapy in Denmark: association to iodization of salt?

et al. 2011

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Iodization of salt is an effective strategy to prevent iodine deficiency disorders. Recent studies, however, indicate that increasing the iodine intake in a population may give rise to an increased incidence of hypothyroidism, but the association has not been fully clarified. In Denmark, iodization of salt was initiated in 1998 because of mild-to-moderate iodine deficiency. The aim of this study was to evaluate the effect of the raised iodine intake on the nationwide incident use of thyroid hormone replacement therapy (levothyroxine) to treat hypothyroidism. Data on all use of levothyroxine was extracted from the Register of Medicinal Product Statistics during the period 1995-2009 and linked to other nationwide registers by use of the Danish identification number. Persons with previous thyroid surgery were excluded. In the studied period 71,565 incident users were identified. The incidence rate increased 75% in the moderately iodine deficient region (72.2 incident users/100,000 person-years in 1997 to 126.6 in 2008) and 87% in the mildly deficient region (86.9-162.9). When stratified by sex and age-group (00-39, 40-64, 65+) the largest relative increase was seen among women in the youngest age-group, where more than a doubling was seen. The mechanisms behind the increase may be a result of iodine-induced hypothyroidism, although a higher diagnostic activity with regard to thyroid dysfunction and intensified treatment of subclinical hypothyroidism may also play a role. Our findings stress the need for caution when initiating iodine fortification programs to keep the intake within the optimal range, and the need for continuous monitoring.

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Section: Discussionsupporting

confidence: 93%

Doubling in the use of thyroid hormone replacement therapy in Denmark: association to iodization of salt?

et al. 2011

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“…Even though it did not reach significance in a relatively small Hungarian sample, a trend towards more individuals with high Tg level in areas with iodine abundance has been demonstrated (29). In a large Chinese study, the median Tg did not differ between three regions with mild iodine deficiency, iodine adequacy and more than adequate iodine intake respectively (30). However, the iodine excess in the Figure 2 The prevalence of elevated serum thyroglobulin in three classes before (nZ4649) and 4 years after (nZ3570) iodization of salt in two regions of Denmark with mild (A) and moderate (B) iodine deficiency.…”

Section: Discussionmentioning

confidence: 89%

Thyroglobulin as a marker of iodine nutrition status in the general population

Vejbjerg

Knudsen

Perrild

et al. 2009

European Journal of Endocrinology

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Objective: The iodine status of a population is traditionally evaluated by either urinary iodine (UI) excretion or by some measure of thyroid volume and the prevalence of goitre. In this prospective study of a mandatory iodization programme, we aimed to evaluate serum thyroglobulin (Tg) as a marker of iodine status in the population. Methods: Two identical cross-sectional studies were performed before (1997-1998, nZ4649) and after (2004-2005, nZ3570) the initiation of the Danish iodization programme in two areas with mild and moderate iodine deficiency. Serum Tg was measured from blood samples. Thyroid volume was measured by ultrasonography. Results: Before iodization, the median serum Tg was considerably higher in moderate than in mild iodine deficiency. Iodization led to a lower serum Tg in all examined age groups. The marked preiodization difference in Tg level between the regions was eliminated. The prevalence of Tg above the suggested reference limit (40 mg/l) decreased from 11.3 to 3.7% (P!0.0001). Using bootstrapping, we demonstrated a higher efficacy of Tg than of thyroid volume to show a difference between pre-and post-iodization values. Conclusion: We found serum Tg to be a suitable marker of iodine nutrition status in the population. The results may suggest that the Danish iodization programme has led to a sufficient iodine intake, even if the median UI excretion is still marginally low according to WHO criteria.

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“…This exceeds the lowest observed adverse effect level for iodine [4], but even less excessive intake levels may associate with an increase in the occurrence of thyroid disease in a population [2]. Considering the different iodine content of tap water in the villages along the Bohai Bay, a survey of these and other Chinese populations may aid the identification of the lowest observed adverse effect level for iodine [3,4].…”

Section: Discussionmentioning

confidence: 92%

“…This area attracts attention because of reports of a high prevalence of goitre [20], a study describing adverse effects of high iodine intake level on serum thyroglobulin [3] and a study showing increased occurrence of hypothyroidism [12].…”

Section: Discussionmentioning

confidence: 99%

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Speciation of Iodine in High Iodine Groundwater in China Associated with Goitre and Hypothyroidism

Andersen

Guan

Wang

et al. 2008

Biol Trace Elem Res

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Iodine intake affects the occurrence of disease in a population. Excessive iodine intake may be caused by a high iodine content of drinking water. Tap water in few locations in Europe contains up to 139 microg/L mostly bound to humic substances, probably leaching from marine sediments in the aquifers. Even higher iodine contents have been found in Chinese waters, previously shown to associate with goitre and hypothyroidism. The aims were to elucidate speciation of high iodine groundwater from deep wells in China and to compare with high iodine waters from Europe. Water was sampled from eight wells in five villages along Bohai Bay, China. Macro-molecules and low molecular weight (MW) substances were separated by size exclusion chromatography (high performance liquid chromatography, Superose 12 HR 10/30, buffer 0.1 M Tris, pH 7.0). Organic material was evaluated by A280 and iodine in fractions measured by the Ce/As method after alkaline incineration. Iodine content of well water varied from 135 to 880 microg/L (median 287 microg/L). The amount of organic material in water was low with A280, <1-5 mAU. The chromatographic traces were similar between samples: One peak of iodine eluted around K (AV) 0.65 corresponding to MW 5 kDa (humic substances) and one peak at V (total) (iodide/low MW substances). The fraction of iodine in macro-molecules, suggested to be humic substances, varied from 8% to 70% (median 27%). Iodine and peak absorbance were associated (p = 0.006). In conclusion, iodine in iodine-rich deep well water in northern China may have marine origin and may associate with humic substances, comparable to shallow well iodine-rich water in Europe. High iodine intake from iodine-rich water suggests the cause of endemic goitre and hypothyroidism in some areas in China being iodine.

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

Cited by 18 publications

References 16 publications

Doubling in the use of thyroid hormone replacement therapy in Denmark: association to iodization of salt?

Doubling in the use of thyroid hormone replacement therapy in Denmark: association to iodization of salt?

Thyroglobulin as a marker of iodine nutrition status in the general population

Speciation of Iodine in High Iodine Groundwater in China Associated with Goitre and Hypothyroidism

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