What was the GRASS trial of selenium supplementation and Graves’ hyperthyroidism?
The GRASS trial was a multi-centre randomized controlled trial. The researchers enrolled 430 individuals with newly diagnosed Graves’ hyperthyroidism. In addition to standard hyperthyroidism medication, the study participants received daily supplementation with 2 x 100 mcg selenium or placebo tablets during 24–30 months, depending on the timing of antithyroid drug withdrawal. The primary outcomes that they measured were 1) rate of remission and 2) quality of life [Cramon 2026].
What selenium preparation did the GRASS trial test?
The researchers used organic selenium in the form of selenium-enriched yeast, consisting mainly of selenomethionine, at a dose of 200 mcg of selenium per day (two 100 mcg tablets).
- Product: Organic selenium (100 mcg tablets).
- Manufacturer: Jemo-Pharm A/S, Stege, Denmark.
- Placebo: Matching tablets made with non-selenium-enriched yeast.
What effects did the GRASS trial show?
As an adjuvant treatment to standard Graves’ hyperthyroidism therapy, the selenium adjuvant treatment did not show any significant effect, compared with placebo, on remission rate and quality of life [Cramon 2026].