Thioredoxin reductase (TrxR) is a pyridine nucleotide-disulphide oxidoreductase that contains selenium. Mammalian TrxRs come in three different isoforms: TrxR1 (TXRND1), TrxR2 (TXNRD2), and TrxR3 (TGR). Thioredoxin (Trx), a redox protein, is reduced by NADPH in a NADPH-dependent manner thanks to TrxRs. TrxR plays a crucial role in controlling the intracellular redox environment, cell division and growth, and the recycling of ascorbate from its oxidized state. Cancers, metabolic syndrome, insulin resistance, type 2 diabetes, hypertension, and atherosclerosis are all linked to the Trx/TrxR system.