The pineal gland is a small gland in the center of the brain. It secretes melatonin, which plays a role in the body’s internal clock.

The primary function of the pineal gland is to control the cycle of waking and sleeping. It forms part of the endocrine system, which is the collection of hormone-secreting glands that regulate bodily processes.

This article discusses the pineal gland and its functions.

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The brain has two hemispheres, connected by a network of fibers. The pineal gland is in the middle of the brain, in between the two hemispheres.

The pineal gland mainly contains pinealocytes, which are cells that produce the hormone melatonin; and glial cells, which are a particular type of brain cells that support neurons.

Neurons are cells that transmit information to other cells via electrical and chemical signals.

The pineal gland is key to the body’s internal clock because it regulates the body’s circadian rhythms. Circadian rhythms are the daily rhythms of the body, including signals that make someone feel tired, sleep, wake up, and feel alert around the same time each day.

These rhythms recur naturally on a 24 hour cycle, even without light fluctuations.

The pineal gland secretes melatonin, which is a hormone that helps regulate circadian rhythms. Melatonin is produced according to the amount of light a person is exposed to.

The pineal gland releases greater amounts of melatonin when it is dark, which points to melatonin’s role in sleep.

Some research, however, suggests that the link between melatonin and sleep might not be as simple as it seems. These researchers found that removing the pineal gland did not affect the activity levels of rats that had normal access to light and dark. They concluded that the function of the pineal gland may be more complicated than initially thought and that its role may vary widely between different animals.

The pineal gland has been linked to a range of other functions. These include:

Bone metabolism

Research on mice suggests that changes in the function of the pineal gland might affect bone metabolism. These findings may apply to humans as well — postmenopausal women are significantly more vulnerable to osteoporosis than other groups.

Pineal gland function tends to decline with age. Researchers concluded that oral melatonin supplements might help increase bone mass, which could be used in the future to protect against postmenopausal osteoporosis.

However, further research is necessary to assess the role of the pineal gland and bone metabolism in humans.

Mental health

Sleep deprivation can cause or worsen mental health conditions. Some mental health disorders may also make it more difficult to sleep.

Access to daylight can also play a role in some mental health conditions.

Seasonal affective disorder, for instance, is a form of depression that affects a person’s mood and tends to occur when light levels are low. This may be due to changes in melatonin secretion.

A 2017 review, however, found no evidence that melatonin had any effect on mood disorders.

Drug metabolism

Some drugs, including both recreational and prescription drugs, appear to alter the function of the pineal gland and change melatonin secretion patterns.

One older study using an animal model suggested that the pineal gland could play a significant role in addiction to cocaine and other psychostimulants.

Aging

As people age, the pineal gland tends to secrete less melatonin. It is unlikely that melatonin is the sole culprit for age-related changes, but reduced melatonin levels may help explain the aging process.

Older adults tend to sleep less and may have trouble falling asleep. Changes in melatonin might explain this phenomenon.

The pineal gland may accumulate calcium deposits. These deposits are normal in healthy individuals, but excessive calcification can prevent the pineal gland from functioning properly.

Because the pineal gland is closely associated with the hypothalamus, problems with the hypothalamus — including cancer, growths, or hormonal issues — can cause pineal gland dysfunction. Pineal gland tumors are rare but can also alter pineal function.

The most prominent symptom of pineal gland dysfunction is a change in circadian rhythms. This might mean sleeping too much or too little, feeling active and restless in the middle of the night, or feeling sleepy at unusual times.

Other symptoms of a problem with the pineal gland include:

  • headache, nausea, vomiting, or tremor
  • difficulty with sense of direction
  • changes in fertility, menstrual cycle, or ovulation
  • osteoporosis
  • mental health issues, particularly seasonal symptoms

More research may reveal additional pineal gland functions and determine how light and melatonin affect everyday health.

The pineal gland is a small gland in the center of the brain. It secretes the hormone melatonin and is primarily responsible for regulating patterns of sleep and waking.

Calcium buildup and cancerous tumors may disrupt pineal gland function, but these are rare.