The pineal gland – the main source of melatonin

In my previous post we mentioned the pineal gland, the main source of melatonin.

But what is the pineal gland? The pineal gland is a very small structure in the brain, roughly 5-9mm in length, and 1-5mm in width. It weighs between 100-180mg1.

The pineal gland is located near the centre of the brain, between the two hemispheres in a region called the epithalamus. The pineal gland is also referred to as the epiphysis cerebri.

Credit: iStock/VectorMine

Pineal glands can vary in size depending on a person’s age. Pineal glands tend to be largest in the 30-50 age group2. Larger pineal gland volume has been associated with greater melatonin secretion. 

Within the pineal gland, you have specialised cells called pinealocytes. There are 2 types of pinealocytes, type 1 and type 2. The function of the pinealocytes is to produce melatonin.

Interestingly, pineal glands can vary in their composition.  In addition to pinealocyte cells, pineal glands can also contain pineal gland cysts, which are fluid filled sacs. The more pineal cysts there are in the pineal gland, the smaller the volume of the melatonin producing pinealocyte cells. Research has shown that more solid pineal glands, i.e. those made up of large volumes of pinealocyte cells, produce more melatonin compared to pineal glands that contain cysts3. The pineal gland can also contain calcium deposits, and these calcifications commonly increase with age1. These calcifications can show up on brain scans such as X-rays, MRI and CT scans. A calcified pineal gland is commonly used by doctors as a landmark on X-rays.

History of the pineal gland

The earliest description of the pineal gland from ancient Greece can be found in the 8th book of Galen’s On the usefulness of the parts of the body, where he gave the name pineal because it is shaped like a pinecone (Latin glandula pinealis).

The pineal gland has previously been known as the “third eye”4. The reason for this could be linked to its location deep within the centre of the brain, and its connection to light through the circadian rhythm and melatonin secretion.

Credit: Shutterstock/luboffke

René Descartes (31 March 1596 – 11 February 1650), was a French philosopher, scientist, and mathematician. He considered the pineal gland to be a structure that connected the soul to the body5.

The pineal gland was the last part of the endocrine system to be discovered.

Is the size of the pineal gland linked to mental illness?

One MRI study from 2015 has found that patients with schizophrenia have significantly smaller pineal gland volumes compared to control subjects. However, this study has limitations in that the findings were from a small sample size of only 17 patients. It has been suggested that the reduced pineal gland volume may be due to delays in the neurodevelopmental process in people with schizophrenia6. Another theory is the neurodegenerative hypothesis for schizophrenia. Neurodegeneration of cells may affect the molecular structure of pineal gland which can cause its size to decrease7.

Another MRI study has found that patients with Alzheimer’s dementia also had smaller pineal gland volumes compared to subjects without Alzheimer’s dementia and those with mild cognitive impairment8.


1. Gheban BA, Rosca IA, Crisan M. The morphological and functional characteristics of the pineal gland. Med Pharm Rep. 2019 Jul;92(3):226-234. doi: 10.15386/mpr-1235. Epub 2019 Jul 31. PMID: 31460502; PMCID: PMC6709953.

2. Golan J, Torres K, Staśkiewicz GJ, Opielak G, Maciejewski R. Morphometric parameters of the human pineal gland in relation to age, body weight and height. Folia Morphol (Warsz) 2002;61:111–113.

3. Nölte I, Lütkhoff AT, Stuck BA, Lemmer B, Schredl M, Findeisen P, Groden C. Pineal volume and circadian melatonin profile in healthy volunteers: an interdisciplinary approach. J Magn Reson Imaging. 2009 Sep;30(3):499-505. doi: 10.1002/jmri.21872. PMID: 19630077.

4. Jackson, S. B. (2020). Rolling My Third Eye: The Third Eye and Pineal Gland Connection. D.U.Quark, 5 (1).

5. Descartes and the Pineal Gland, The Stanford Encyclopedia of Philosophy

6. Fındıklı E, Inci MF, Gökçe M, Fındıklı HA, Altun H, Karaaslan MF. Pineal gland volume in schizophrenia and mood disorders. Psychiatr Danub. 2015 Jun;27(2):153-8. PMID: 26057310.

7. Gupta S, Kulhara P. What is schizophrenia: A neurodevelopmental or neurodegenerative disorder or a combination of both? A critical analysis. Indian J Psychiatry. 2010 Jan;52(1):21-7. doi: 10.4103/0019-5545.58891. PMID: 20174514; PMCID: PMC2824976.

8. Matsuoka T, Imai A, Fujimoto H, Kato Y, Shibata K, Nakamura K, Yokota H, Yamada K, Narumoto J. Reduced Pineal Volume in Alzheimer Disease: A Retrospective Cross-sectional MR Imaging Study. Radiology. 2018 Jan;286(1):239-248. doi: 10.1148/radiol.2017170188. Epub 2017 Jul 26. PMID: 28745939.



The articles in the Sleep Psychiatrist blog have been written by Dr Dipesh Mistry. They are for educational and informational purposes only, and should not be regarded as medical advice. Always seek advice from your sleep physician, personal physician, psychiatrist, or any other suitably qualified healthcare professional in relation to any interventions or treatment for your sleep, mental health or physical health.

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