ReverseT3 is a thyroid hormone that "puts the brakes" on metabolism, in a sense putting things into reverse until particular conditions resolve. Increased rT3 production may be a way for the body to preserve protein and energy during stress.
rT3 is inactive, but can make up approximately one third of thyroid hormone in circulation, suggesting its presence is important. Reverse T3 is produced from T4, with an estimated one third of T4 converted to T3 and one third converted to reverse T3.
Low levels of rT3 an be seen with central hypothyroidism (due to pituitary or hypothalamic dysfunction), HIV infection, and the use of certain tricyclic antidepressants.
Elevated rT3 can be seen with stress, starvation, carbohydrate restriction, glucose dysregulation, liver disease, heart failure, aging, selenium deficiency, T4 monotherapy, and the use of certain medications such as amiodarone and glucocorticoids.
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