Endocrine Abstracts

Objectives: Iodine fortification (IF) induces an initial increase followed by a decrease in the incidence of hyperthyroidism in the population. Also, the sex-, age-, and subtype distribution of hyperthyroid cases changes after IF. The risk of atrial fibrillation (AF) in hyperthyroid patients is influenced by these factors. Therefore, we aimed to examine how the association between incident hyperthyroidism and atrial fibrillation was affected by an IF increasing the population intake from moderate-mild iodine deficiency to low-adequacy.

Methods: Incident hyperthyroid patients were included at the date of first in- or outpatient diagnosis, and AF within 3 months before to 6 months after the index date was identified by in- and out-patient hospital diagnoses in Danish nationwide registers, 1997-2018. The relative risk (RR) of AF each calendar year (reference year: 1997, IF introduced in 2000) was analyzed by Poisson regression models adjusted for age, sex, educational level, geographic region, and comorbidities.

Results: Overall, out of 62,201 patients with incident hyperthyroidism, 7.66% (95%CI 7.45-7.87) had AF. There was a non-significant increased risk during the first years after IF followed by a gradual decrease in the risk of AF to RR 0.72 (95%CI 0.52-0.79) in 2017. There was no statistically significant difference in the development in the risk of AF by sex, age group, or region (moderate vs mild iodine deficiency before IF).

Conclusions: Results indicate that IF may reduce the risk of concomitant AF in hyperthyroid patients. If these results are confirmed, IF may not only reduce the population incidence of hyperthyroidism but also reduce the burden of morbidity in remaining hyperthyroid patients.