The incidence of hyperthyroidism in Austria from 1987 to 1995 before and after an increase in salt iodization in 1990

Abstract

Between 1963 and 1990, Austria had iodized salt prophylaxis of endemic goitre with 10 mg KI (7.5 mg I) per kg. This was obviously insufficient, as urinary iodine excretion ranged from 42 to 78 microg I per g of creatinine and goitre in adults remained in the endemic range of 15%-30%. Therefore salt iodization was doubled in 1990. The aim of this study was to assess the annual incidence of different types of hyperthyroidism (HT) before and after this increase in salt iodization. The incidence of HT was recorded in 14 nuclear medicine centres from 1987 to 1995. In five additional centres data were available from 1992 onwards. Data prior to 1992 were documented retrospectively, while those after 1992 were recorded prospectively. The 14 centres drew patients from an area with a population of approximately 4.23 million while all 19 institutes were estimated to cover an area with a population of 5.4 million (the total population of Austria is 7.86 million). A total of 414232 persons were examined for the first time in the participating centres. HT and the type of HT were defined by clinical examination, serum TSH, thyroid hormone levels in blood, ultrasonography, scintigraphy and serum autoantibody titres. HT was classified into immunogenic HT (Graves' or Basedow's disease, GD) and HT with intrinsic thyroid autonomy (uni-, multinodular or disseminated Plummers' disease, PD). HT was also divided into overt (o) or subclinical (sc) disease. The following data were calculated: annual incidence per 100000 and the relative risk (RR) for HT with 95% confidence intervals (CI). In addition, linear trends were calculated for each type of HT by means of logistic regressions. In the 19 centres a total of 47834 patients with HT were registered from 1987 to 1995. PD accounted for 75% of all cases of HT and GD for 19%, while other types of HT were present in 6%. From 1987 to 1989 (time period T0), the annual incidence of oPD was 30.5 (95% CI 29.6-31.5) per 100000. The RR compared to the baseline period T0 was highest in 1992 (1.37; 1.3-1.45) and decreased to 1.17 (1.1-1.24) in 1995. The annual incidence of scPD in T0 was 27.4 (26.5-28.3) per 100000. The RR was highest in 1991 (1.64; 1.56-1.73) and was 1.60 (1. 51-1.69) in 1995. In oPD and scPD a higher RR was observed in persons older than 50 years of age, particularly in men. The incidence of oGD in T0 was 10.4 (9.8-10.9) per 100000; the maximum RR increased to 2.19 (2.01-2.38) in 1993 and decreased to 1.95 (1.78-2.13) in 1995. The incidence of scGD was 1.9 (1.6-2.1) in T0. The maximum RR was observed in 1994 (2.47; 2.04-3.0) and it was still 2.26 (1.85-2.77) in 1995. The increased incidence of oGD and scGD was evenly distributed in all ages and both sexes. The time course of different types of HT following the increase in salt iodization could be divided into two phases: an increase in the incidences of HT with peaks after 1-4 years and a subsequent decrease, the only exception being scGD. The effect was more pronounced in GD than in PD. PD showed an age and gender dependency over ...

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

“…Our results parallel the findings from Denmark that Graves' disease was the dominant type of hyperthyroidism in the area with excessive iodine intake (9). However, the similar prevalence of Graves' disease independent of the iodine intake was not in agreement with the findings from Austria (6). Other findings in our study demonstrated that the higher prevalence of hypothyroidism due to autoimmune thyroiditis (Hashimoto disease and atrophy thyroiditis) was closely related with the increase in iodine intake although no difference was found in the prevalence of thyroid autoantibodies in the general population among the three areas (17).…”

Epidemiology of subtypes of hyperthyroidism in Denmark: a population-based study

“…The incidence of MNTG in Denmark (34.6 per 100 000 person-years) is higher than in most other countries studied, where the calculated SIRs spanned from 3.3 to 30.5 per 100 000 person-years (6,8). All these studies were performed in regions with a higher iodine intake in the population compared with Denmark.…”

“…The sensitive design used in the present study may be responsible for the high incidence compared with previous Danish studies Female 0 5 110 169 177 204 224 277 195 27 1388 Male 0 2 15 31 32 51 54 77 30 2 294 Multinodular toxic goitre Female 0 0 0 11 31 86 110 206 170 27 641 Male 0 0 1 1 4 14 18 39 21 2 100 Graves' disease Female 0 5 82 122 102 70 69 56 12 0 518 Male 0 1 12 20 21 25 17 24 162 47 901 41 506 33 092 32 420 23 355 23 506 15 257 (6,43) and above 100 after excessive iodine exposure in Tasmania (44). A comparison between these studies and the present study is difficult, as they differ with regards to the design.…”

“…Hyperthyroidism may be divided into a number of nosological subtypes with different aetiology, clinical presentation, prognosis and outcome of therapy. The incidence of individual subtypes may also be dependent on the iodine intake level (3,5,6). However, the information on the epidemiology of subtypes of hyperthyroidism and the effect of environmental factors including iodine intake is limited.…”

“…Other studies only evaluated certain age groups (8). Most studies were based on patients referred to hospital departments (6,(9)(10)(11)(12)(13)(14)(15)(16)(17)(18), potentially leading to referral bias (19).…”