Iodine status and iodine pool an a small community in western Sweden
Abstract: Iodine is essential in the synthesis of the vital hormones of the thyroid gland. On a worldwide basis, iodine deficiency is the global most important cause of thyroid disease. The most common disorder is development of goitre, but most important is the brain damage in children caused by low thyroid hormone levels during preg-nancy in women with pronounced iodine deficiency, where cretinism is the most severe form. Iodine defi-ciency used to occur in Sweden, but following the introduction of a national programme of iodine supplemen-tation in 1936 with 10 mg/kg of table salt and an increase in the level to 50 mg/kg in 1966, Sweden is regarded as iodine replete. However, no monitoring programme is currently in progress and the actual iodine status of the population is therefore unknown. The aim of this thesis was to evaluate the effect of iodine supplementa-tion in a small community in western Sweden. Methods: Three age groups, each comprising 60 individuals were chosen, Group 1: 7-9 years, Group 2: 15-17 years and Group 3: 60-65 years old. Thyroid volume by ultrasonography and urinary iodine were measured in all groups. In the young people and adults, blood samples were collected for analyses of TSH, total and free T4, total and free T3 and TPOAb. In the elderly group, a radionuclear investigation was also performed com-prising scintigraphy and 24h 131-I uptake. The iodine contnet of the thyroid gland was determined by X-ray fluorescence (XRF). The 24h 131-I uptake was compared with that of a consecutively measured group of patients with Graves¡¦ disease patients referred for treatment and with data retrieved from 1955. Results: The median for urinary iodine concentration in the three age groups was 194 ƒÝg/L (Group 1), 246 ƒÝg/L (Group 2) and 190 ƒÝg/L (Group 3), indicating an adequate iodine intake well above the WHO definition of iodine deficiency, < 100 ƒÝg/L. The median thyroid volumes were 4.7 mL (Group 1), 11.5 mL (Group 2) and 14.3 mL (Group 3), which are within established reference volumes. The mean 24h 131-I uptake for the euthy-roid individuals was 21%, while it was 61% for the Graves¡¦ patients. In 1955, the uptake was higher, 38% and with a wider range, in the euthyroid subjects, whereas, in the hyperthyroid patients, it was similar, 62%, to recent recorded values. The X-ray fluorescence (XRF) analyses revealed a mean thyroid iodine concentration of 0.6 mg/mL and a mean total iodine content of 8.6 mg, which is in accordance with other internationally, published data. There was a pronounced variation in the thyroid iodine content between individuals. Four teenagers (7%) had an elevated TPOAb concentration, three of the subjects being girls (8%). 29% of the adult women had elevated TPOAb. Conclusion: Urinary iodine concentration and thyroid volumes were within the recommended reference values in WHO guidelines. The 24h 131-I uptake values confirm that the iodine intake in this community is sufficient. No correlation was found between intrathyroidal iodine, iodine uptake and urinary iodine, also indicating iodine sufficiency. We conclude, that the inhabitants of the community studied, has a sufficient iodine intake. There is a need of a more extensive nation-wide evaluation of iodine status.
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