Objective: To assess the prevalence of hyperthyroidism just after implementation of iodine prophylaxis among adults from an area with iodine deficiency. Study design and subjects: A total of 1648 adults (age 16 years and older) were sampled from an area of southern Poland during two nationwide epidemiological surveys. Of these, 1424 adults with negative medical history for thyroid disorders qualified for final analysis. The authors compared thyroid dysfunction in participants prior to (1989-1990) and after implementation of iodine prophylaxis (1997-1999). Setting: The southern part of Poland. Results: We found an increase in the serum concentration of anti-thyroid microsomal antibodies from 4.9% in the years 1989-1990 to 12.1% after introduction of iodised household salt (P < 0.0001). The prevalence of hyperthyroidism (defined as thyroid-stimulating hormone <0.4 μ U ml -1 ) significantly increased in the equivalent period from 4.8 to 6.5% (P = 0.009). Conclusions: We concluded that a sudden rise in iodine intake after implementation of iodine prophylaxis among adults from the area with iodine deficiency may lead to an increase in thyroid autoimmunity and prevalence of hyperthyroidism. Those possible early side-effects appear to be only temporary and are acceptable when compared with the evident benefits of adequate iodine intake.

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Increased prevalence of hyperthyroidism as an early and transient side-effect of implementing iodine prophylaxis

Objective: Most of the Polish territory has been classified as an iodine-deficient and endemic goiter area according to the International Council for Control of Iodine Deficiency (ICCIDD) criteria. In 1997 the obligatory model of iodine prophylaxis was implemented. Our investigations were aimed at the effectiveness of iodine prophylaxis in Poland. Methods: We assessed urinary iodine excretion and goiter prevalence in 5663 children aged 6–12 yr. The population of children from the same 27 schools was investigated from 1992 to 1994 (1406 girls and 1244 boys) and from 1999 to 2005 (1563 girls and 1450 boys) using identical laboratory and ultrasound methods. Results: We found significant increase in iodine urinary concentration (median 52 μg/l vs 93 ug/l, p<0.001) with accompanying drop in goiter prevalence (29.6% vs 5.2%, p<0.001) after implementation of iodine prophylaxis. Iodine excretion distribution changed significantly after 1997 with an increase in the percentage of children with iodine urinary concentration above 100 μg/l from 10.8% to 45.4%, respectively. A significantly higher iodine urinary concentration was observed in lowlands compared to uplands both before and after implementation of iodine prophylaxis (median, 50 νg/l vs 57 μg/l and 86 μg/l vs 114 μg/l, respectively, p<0.001). The goiter prevalence did not differ between girls and boys from 1992 to 1994 (28.8% vs 30.5%, p=0.35) and 1999 to 2005 (5.5% vs 4.9%, p=0.45). Conclusions: Implementation of the new model of iodine prophylaxis in Poland in 1997 has led to significant increase in iodine urinary concentration and decrease in goiter prevalence among Polish schoolchildren. In the youngest group of children (6–8 yr olds), prevalence of goiter decreased to 3.2% — i.e. below endemic levels.

Effectiveness of the iodine prophylaxis model adopted in Poland

Following the Czernobyl accident, an epidemiologic study was undertaken in which the daily iodine intake was estimated in 15% of the population studied. Iodine excretion was measured in single morning urine specimens. The iodine content was also assessed in the water form wells and in cow-milk at farms in randomly chosen villages in the region of Krynica and Nowy Sacz. On the basis of a 24-hour diet recall, the mass of each food product consumed daily was estimated for 483 persons in the Krakow voivodship (14.4% of the total population) and for 397 persons in the Nowy Sacz voivodship (15.8% of the total population). Using this data, the nutrient content of the daily diet was calculated for each studied individual. Measurements of iodine content in water and cow-milk show relatively lower iodine levels in the Nowy Sacz voivodship. The estimated value of the iodine content in milk (5.5 micrograms/100 g of milk) was considered in the estimates of the chemical composition of the daily diet of the inhabitants of this region. The mean values of the daily energy as well as the protein and calcium consumption in all subpopulations grouped with respect to domicile, age and sex, fell within the recommended daily allowances for these groups. The iodine content, while widely scattered, concentrated around low values. The median values of the iodine content in children of age 3-10 years, age 10-16 years and in adults, were 66%, 48% and 25-40% of the recommended daily allowances, respectively. No particular differences in the food intakes were observed between inhabitants of Krakow and Nowy Sacz voivodships. Nor were significant differences found in the urine iodine excretion in groups of these regions. The low iodine content in the daily food intake may be an essential factor in the ethiology of the increasing number of thyroid goiter.

[Evaluation of iodine levels in daily dietary intake and urine of persons participating in epidemiological studies in the Krakow macro-region after the disaster in Czernobyl and level of iodine in drinking water of that region].

Dłuzniewska K

Papers

[Evaluation of iodine levels in daily dietary intake and urine of persons participating in epidemiological studies in the Krakow macro-region after the disaster in Czernobyl and level of iodine in drinking water of that region].