Selenium supplementation in individuals with newly diagnosed Graves' hyperthyroidism: a double-blind, multi-centre RCT.

Purpose: We examined the effect of selenium vs placebo on remission rate and quality of life (QoL) in the Graves' selenium supplementation (GRASS) trial (ID: NCT01611896). Methods: Double-blinded, placebo-controlled, multi-centre trial in individuals with newly diagnosed Graves' hyperthyroidism randomised to daily supplementation with 200 μg selenium or placebo tablets during 24-30 months, depending on the timing of antithyroid drug (ATD) withdrawal. The primary outcome was the proportion of participants with non-remission, defined as receiving ATD or remaining hyperthyroid (thyroid stimulating hormone <0.1 mIU/L) during the last 12 months of the intervention period or referral to ablative therapy (radioactive iodine or surgery). QoL was serially assessed by the thyroid-related patient-reported outcome ThyPRO and compared with previously collected norm data. Results: Between Dec 7th 2012 and Dec 3rd 2018, 430 participants with Graves' hyperthyroidism were recruited. Non-remission was observed in 114 (53.3%) participants in the placebo group and 118 (54.6%) in the selenium group (OR = 1.0 (95% CI: 0.7-1.5); P = 0.98). There was no beneficial effect of selenium, as compared with placebo, on any ThyPRO scale. The participants' QoL at the end of the study was comparable to that of the general population sample. Thyrotropin receptor antibody levels were similar in the groups at the 18-month and end-of-study follow-up visits. Conclusion: In individuals with newly diagnosed Graves' hyperthyroidism, daily supplementation with selenium did not have any effects compared with placebo as add-on to standard antithyroid drugs. The GRASS trial findings do not support the use of selenium supplementation in Graves' hyperthyroidism.