The Importance of the Pineal Gland

Letters to the Editor regarding the article The Function of Sleep and the Treatment of Primary Insomnia by Prof. Dr. med. Wolfgang Freund and PD Dr. med. Frank Weber in issue 50/2023

We thank the authors of the article (1). Sleep does without a doubt have highly relevant, complex functions that are nowhere near fully known. The knowledge gap that the authors pointed out weigh all the more heavily as a consequence.

It stands to reason that the pineal gland has an important role in this context (2), but surprisingly it deserved only a marginal note, even in this comprehensive literature review “[. . . ] the pineal gland secretes melatonin, which serves a signal for the body to go to sleep” and “Melatonin regulates the circadian rhythm and is approved in Germany as a drug for the treatment of primary insomnia . . . […]”.

The actual signal for the body to go to sleep is the (absence of) light leaks via the retino-hypothalamic system, especially the suprachiasmatic nucleus (SCN). This is our biological clock and the central location for the “on-off” switch of melatonin synthesis—rather than the light, which modulates as a trigger melatonin synthesis via the SCN (3).

Melatonin is the sleep hormone per se. In addition to regulating the sleep-wake rhythm it has multiple effects, including anti-inflammatory, antioxidant, antitumor, and neuroprotective effects. The statement that “its general efficacy is considered weak” is an abbreviated explanation: the lacking evidence of successful melatonin substitution is more a function of technical deficits of studies—for example, the pharmacokinetic particularities of absorption and half-life or problems with measurements, the complexity of the study parameters, and deficiencies in practical use. Recent publications have found sources of melatonin production outside the pineal gland—such as the microbiota—with completely new aspects of regulation and interaction of the different organ systems, while also considering (disrupted) sleep-wake cycles (4).

The pineal gland obviously has not been given the importance it should have, not only as far as the clinical relevance of sleep quality or sleep disorders is concerned, but also in the interdisciplinary setting. The exceedingly large number of people seeking advice or who are affected would greatly benefit from increased interest in and engagement for this central organ.

DOI: 10.3238/arztebl.m2024.0028

Dr. med. Bernhard Hauns

Pinealishilfe e. V.

Mühlhausen-Ehingen

Conflict of interest statement

BH is the chairman of the board of the Pinealishilfe e.V. (a German pineal gland charity).

References

1. Freund W, Weber F: The function of sleep and the treatment of primary insomnia. Dtsch Arztebl Int 2023; 120: 863–70

2. Wisneski LA, Anderson L: The scientific basis of integrative medicine. Second edition. London, New York: CRC Press, Taylor & Francis Group 2009.

3. Thomas CE, Russel JR: Melatonin: a universal time messenger . Neuro Endocrinol Lett 2015; 36: 187–92.

4. Tan DX, Russel JR, Zimmerman S, Hardeland R: Melatonin: both a messenger of darkness and a participant in the cellular actions of non-visible solar radiation of near infrared light. Biology 2023; 12: 89