Thyroid hormones paradox, oxidative stress, and selenium

Reactive oxygen species (ROS) play an important role in physiological processes, but - when being in excess - ROS cause oxidative damage to molecules. Under physiological conditions, the production and detoxification of ROS are more-or-less balanced. Also in the thyroid, ROS and free radicals participate in physiological and pathological processes in the gland. For example, hydrogen peroxide (H2O2) is crucial for thyroid hormone biosynthesis, acting at different steps of the process. Additionally, H2O2 is believed to participate in the Wolff-Chaikoff`s effect, undergoing in conditions of iodide excess in the thyroid. It is the purpose of this review to attempt a synthesis of what we currently know of thyroid hormones production and their relation to oxidative stress and selenium, a trace element.Biomedical Reviews 2009; 20: 17-29