Once called the 'third eye,' the pineal gland is a small gland located deep in the center of the brain. Named for its pinecone shape, this gland secretes melatonin, which plays a role in the body's internal clock.

The pineal gland was one of the last brain organs to be discovered and has been the subject of much mythology and speculation. The seventeenth-century French philosopher Rene Descartes thought the soul was located in the pineal gland.

Pineal gland highlighted in model of human brain. Dactylitis <br>Image credit: Life Science Databases(LSDB), (2009, September 20)</br>Share on Pinterest
The pineal gland is located in the brain, between the right and left hemispheres.
Image credit: Life Science Databases (LSDB), (2009, September 20)

The brain is comprised of two distinct hemispheres connected by fibers.

The pineal gland is located in the middle of the brain, in between the two hemispheres.

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

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.

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. Many supplement manufacturers offer melatonin as a "natural" sleep aid.

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

Share on Pinterest
Decline in pineal gland functioning with age may affect bone metabolism.

Research on mice suggests that changes in the function of the pineal gland might affect bone metabolism. Postmenopausal women are significantly more vulnerable to osteoporosis than other groups.

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

Mental health

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

Some mental health conditions have been linked to access to light. 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.

Pituitary gland function

The pituitary gland is a gland that protrudes from a part of the brain called the hypothalamus. The hypothalamus is linked to a wide range of hormonal functions, including growth and thyroid function. Older research suggests that the pineal gland can alter the behavior of the pituitary gland.

Melatonin may block the pituitary gland from secreting hormones that play essential roles in the development of the ovaries and testes and regulate functions such as the menstrual cycle.

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 study concluded 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 levels of melatonin 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.

Sense of direction

An older study of people with impaired pineal glands found that damage to this gland is associated with declines in the sense of direction.

This suggests that the pineal gland may play a largely unrecognized role in spatial navigation.

Share on Pinterest
Pineal gland dysfunction may affect sleeping patterns. Symptoms may include insomnia or excessive sleepiness.

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

The pineal gland is indispensable to a process most people take for granted: maintaining a consistent schedule from day to day. Without it, the body would struggle to sleep and wake at the same time, and might not know how to respond to changes in light levels properly.

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