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REVIEW. Melatonin and the thyroid gland
Andrzej Lewinski1, Malgorzata Karbownik
1Department of Thyroidology, Institute of Endocrinology, Medical University of Lodz, Poland. alewin@csk.am.lodz.pl
Abstract:
This review briefly summarizes the published data on relationships observed between melatonin - the main pineal hormone, and the thyroid gland. The prevailing part of the survey is devoted to thyroid growth processes and function. A large experimental evidence exists suggesting the inhibitory action of melatonin on thyroid growth and function; this effect has been revealed by using different experimental models: by chronic and short-term melatonin administration in vivo, by light restriction, which is known to increase the activity of the pineal gland, by pinealectomy, etc., as well as by employing the in vitro conditions. Thus, much information has been accumulated, indicating - in experimental conditions - a mutual relationship between the pineal gland and the thyroid. The confirmation of these relations in clinical studies in humans meets numerous difficulties, resulting - among others - from the fact that, nowadays, human beings, as well as certain animal species, used in experimental studies, have been living far away from their natural and original habitat. It makes almost impossible to compare the results obtained in particular studies performed in different species, on the pineal-thyroid interrelationship.
Insights
Melatonin, the pineal hormone, appears to inhibit thyroid gland growth and function in experimental settings. However, confirming this pineal-thyroid relationship in humans is challenging due to environmental factors.
Area of Science:
- Endocrinology
- Neuroendocrinology
Background:
- The pineal gland produces melatonin, a hormone influencing various physiological processes.
- The thyroid gland regulates metabolism and growth.
- Interactions between the pineal and thyroid glands have been investigated.
Purpose of the Study:
- To review and summarize existing data on the relationship between melatonin and the thyroid gland.
- To focus on the impact of melatonin on thyroid growth and function.
Main Methods:
- Review of published experimental data.
- Analysis of studies involving melatonin administration (in vivo and in vitro).
- Consideration of experimental models such as light restriction and pinealectomy.
Main Results:
- Substantial experimental evidence suggests melatonin inhibits thyroid growth.
- Melatonin also appears to suppress thyroid function based on experimental findings.
- A mutual relationship between the pineal gland and thyroid is indicated under experimental conditions.
Conclusions:
- Experimental data strongly support an inhibitory role of melatonin on the thyroid gland.
- Clinical confirmation of the pineal-thyroid relationship in humans is difficult.
- Environmental and habitat differences complicate the comparison of human and animal study results.