As Frontiers in Endocrinology (2023) confirmed: "Most known selenoproteins, such as glutathione peroxidase, are expressed in the thyroid and are involved in thyroid hormone metabolism, redox state regulation, and maintenance of cellular homeostasis." In other words, selenium's documented benefits for Hashimoto's thyroiditis are mechanistically dependent on adequate glutathione availability
Lutgen V, Qualmann K, Resch J, Kong L, Choi S, Baker DA
Third is labs through a trusted channel or your physician to confirm what your body is missing rather than what marketing says you need
Cysteinylation of MHC class II ligands: peptide endocytosis and reduction within APC influences T cell recognition
Glutathione levels were significantly decreased after treatment with IS at CKD concentrations in LLC-PK1 proximal tubular cells [90]