Ten-year follow-up of thyroid epidemiology in Slovenia after increase in salt iodization

Abstract

AimTo assess iodine supply and follow thyroid epidemiology for ten years after an iodine increase from 10 to 25 mg of potassium iodide per kilogram of salt in 1999.MethodsIn 2002 and 2003, we determined the thyroid size by palpation and ultrasound and measured urinary iodine concentration (UIC) in 676 schoolchildren from 34 schools throughout Slovenia. From 1999 to 2009, we followed the incidence of diffuse and nodular goiter, thyroid autonomy, Graves’ disease, and Hashimoto’s thyroiditis among adults in the stable catchment area of the University Medical Centre Ljubljana with 1 000 000 inhabitants.ResultsIn children, only 1% had a goiter grade 2 (visible and palpable thyroid gland), median thyroid volume was 5.8 mL, and median UIC was 148 µg/L. In adults, the incidence of diffuse goiter and thyroid autonomy decreased significantly (2009 vs 1999, rate ratio [RR], 0.16; 95% confidence interval [CI], 0.12-0.21 and RR, 0.73; 95% CI, 0.62-0.86, respectively), with a lower incidence in younger participants in 2009 (P < 0.001). The incidence of multinodular goiter and solitary nodule increased (2009 vs 1999, RR, 1.55; 95% CI, 1.35-1.79 and RR, 1.72; 95% CI, 1.49-1.99, respectively). No long-term changes were observed for Graves’ disease (2009 vs 1999, RR, 0.95; 95% CI, 0.81-1.13), while the incidence of Hashimoto’s thyroiditis increased strongly (2009 vs 1999, RR, 1.86; 95% CI, 1.64-2.12).ConclusionsThe change from mildly deficient to sufficient iodine supply was associated with a marked change in the incidence of thyroid epidemiology – a significant decline in the incidence of diffuse goiter and thyroid autonomy and a marked increase in the incidence of Hashimoto’s thyroiditis.

Epidemiological trends of iodine-related thyroid disorders: an example from Slovenia

“…As for Hashimoto's thyroiditis, its incidence in Slovenia more than doubled after the increase in iodine supply (19). These findings confirm Iranian reports of up to four-fold increase in the prevalence of thyroid autoantibodies after the improvement of iodine prophylaxis in iodine-deficient areas (30).…”

“…In pregnant women, it was also high enough -170.5 µg g -1 of creatinine in the third trimester, and 144 µg g -1 of creatinine after childbirth (22). The volume of the thyroid gland in schoolchildren decreased to 5.8 mL (19).…”

“…Measurements since 1999 show a daily intake of 9.4 g of kitchen salt in girls and 11.5 g in boys (20) and 9.9 g in women and 13.0 g in men (21). As soon as 2003, UIC in schoolchildren increased to 148 µg L -1 , which suggests adequate iodine intake (19). In pregnant women, it was also high enough -170.5 µg g -1 of creatinine in the third trimester, and 144 µg g -1 of creatinine after childbirth (22).…”

“…In 1991 to 1994, we measured UIC in a population of 1740 schoolchildren to be 82.9 µg g -1 of creatinine (18,19), which suggested a mild iodine deficiency. The average volume of their thyroid gland, measured by ultrasound, was 7.2 mL.…”

Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from areas with high iodine drinking water concentrations

“…A total goiter rate (TGR) .5% is one of the criteria for defining iodine-deficient populations (4). Since the advent of iodine fortification around the world, TGRs have greatly decreased while urine iodine concentration (UIC) has increased (6)(7)(8). In China, since salt iodization was implemented in 1996, the median UIC for children aged 8-10 y has been 239 mg/L, and the TGR in children is 2.4% (9).…”