Geographic variations in the frequency of thyroid disorders and thyroid peroxidase antibodies in persons without former thyroid disease within Germany

Abstract

Objective: To investigate regional variations in the frequency of undiagnosed thyroid disorders among 25-to 88-year-old men and women in two communities in the northeast and the south of Germany. In addition, autoantibodies to thyroperoxidase (TPO-Abs) and urinary iodine excretion were determined. Methods: Two population-based surveys of men and women using a common standardized protocol, the Study of Health in Pomerania (SHIP) in the northeast of Germany (2505 participants) and the Kooperative Gesundheitsforschung in der Region Augsburg (KORA) in the south of Germany (2316 participants), were compared with regard to the frequency of undiagnosed thyroid disorders. Results: Compared with the northeast of Germany, urinary iodine excretion and serum thyroidstimulating hormone (TSH) levels were significantly higher in the south. The median urinary iodine concentration was 110 mg/l (64; 169 mg/l) in SHIP and 151 mg/l (97; 214 mg/l) in KORA, and the median TSH value was 0.81 mIU/l (0.56; 1.15 mIU/l) in SHIP and 1.22 mIU/l (0.84; 1.80 mIU/l) in KORA. The frequency of elevated TSH (TSH R2.12 mIU/l) was 4.3% in SHIP and 14.1% in KORA (P!0.001); the corresponding values for suppressed TSH (!0.25 mIU/l) were 3.5 and 1.7% (P!0.001). The proportion of ultrasonographic findings was 55.5% in SHIP and 68.0% in KORA. The frequency of serum TPO-Abs did not differ significantly between northeast and south Germany. Conclusions: There were considerable regional disparities in the frequency of thyroid disorders within Germany. These differences can be explained not only by different regional histories of natural iodine deficiency but also by current differences in the iodine supply under an identical nationwide iodine fortification program.

Shift of the TSH reference range with improved iodine supply in Northeast Germany

“…Thus, there might be differences in iodine supply across the regions of Germany (23). However, our new established reference range for serum TSH levels showed good agreement with recent reference ranges established in East (7) and South Germany (35).…”

“…After the persistence of improved iodine supply for several years, it can be expected that the TSH distribution in the general population shifts toward the right, which has already been observed in Germany (23,24). Thus, the TSH reference interval established during the transition phase between iodine deficiency and sufficiency may not reflect the current distribution of TSH values in the general population of Germany, which might result in unnecessary clinical work-up and high costs for the German health care system.…”

Heredity and lifestyle in the determination of between-subject variation in thyroid hormone levels in euthyroid men

“…However, the iodine:creatinine ratio was negatively associated with FT 4 and rT 3 in our study. Studies longitudinally evaluating subjects after iodine fortification have shown a rather surprising positive association between urinary iodine excretion and TSH levels (34,50). In iodine-sufficient populations, findings suggest a positive linear relation between iodine levels and TSH (36), whereas in subjects with urinary iodine excretion below 50 mg/24 h (moderate iodine deficiency), a negative correlation between urinary iodine and TSH was observed (55).…”

“…Notwithstanding the rather narrow age range in our study population, we observe inverse associations between increasing age and TSH as well as THs. Previous studies on this topic have not been straightforward: both an increase as well as a decrease in TSH with progressing age has been observed (29,30,34,50). Differences in iodine status of a population might be an explanation for this paradox as well as the thoroughness of exclusion of subjects with thyroid auto-immunity.…”

Metformin inhibits goitrogenous effects of type 2 diabetes

“…As with the whole of Germany, the region was formerly iodine deficient until the mid1990s, when an iodine fortification program became effective (17). Particularly among older persons, goiter prevalence is still high (18).…”