Melatonin and the Thyroid Gland - an Overview

In this review, published data on the relationship occurring between melatonin - the main pineal hormone - and the thyroid gland, are briefly summarized. Numerous experimental data suggest an inhibitory influence of melatonin on thyroid growth and secretion. These effects have been presented in different experimental models in vivo and in vitro, the former including short-term and/or chronic melatonin administration to various animal species, in pinealectomized animals, also following light restriction which is known to increase the activity of the pineal. On the other hand, stimulatory effects of thyroid hormones on the pineal growth and function have been demonstrated. Oxidative stress is involved in physiological and pathological processes in the thyroid gland. Recent results of experimental studies suggest that melatonin can protect against oxidative damage in the thyroid. A confirmation of the mutual relationship between the pineal gland and the thyroid is - in clinical studies, in humans - rather difficult, as both human beings and animal species used in experimental studies, live far away from their natural/original habitats. It makes almost impossible to compare the results of studies on the pineal-thyroid interrelationship, obtained in particular experiments in different animal species.