Nationwide trends in surgery and radioiodine treatment for benign thyroid disease during iodization of salt

Objective: Iodization of salt was introduced in Denmark in 1998 because of mild-to-moderate iodine deficiency (ID). The aim of this study was to analyze the utilization rate of surgery and radioiodine therapy for benign thyroid disorders before and after the introduction of iodization, and to study a possible association between the changes and the raised iodine intake. Design: A nationwide register study. Methods: Information on operations and radioiodine treatments for benign thyroid disorders was extracted from nationwide registers in the years 1990 to 2007. Treatment rates are presented for surgery and for radioiodine separately, and as a combined rate, both nationwide and split by the regions of prior mild and moderate ID. Results: A total of 65 605 treatments were identified: 26 456 operations and 39 149 radioiodine treatments. In the first years of iodization (1998-2000; rate ratio 2000/1997), the combined treatment rate increased with 2.5% (95% confidence interval (CI): K1.8-7.1). Split by prior ID level, the increase was seen in the region of moderate ID, but a decrease was seen in the region of mild ID. After 2000, the combined rate decreased, and ended up being 11.1% (95% CI: 7.1-15.0) lower in 2007 than before iodization (rate ratio 2007/1997). The changes were primarily due to changes in the use of radioiodine therapy as the surgery rates remained almost constant. Conclusions: Iodization seemed to be associated with a temporary increase in the utilization rate of surgery and radioiodine therapy in the region of prior moderate ID, probably as a result of treatment of iodine-induced hyperthyroidism, but the rates ended up being lower than before iodization.