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What is Melatonin?

By Dr Ananya Mandal, MD

Melatonin is a hormone that is secreted by the pineal gland. The pineal gland is a small gland that lies within the brain. It acts as a “chronobiotic” in the body. This hormone in other words helps in maintaining the normal circadian rhythms.

Melatonin secretion

Melatonin is secreted by the pineal gland in the brain.

The secretion of the hormone occurs in response to the light and dark cycles. Normally, its production is reduced by being in bright light. On the other hand, being in darkness stimulates melatonin release. This is why it is often called ‘the hormone of darkness’.

Melatonin and the skin

Melatonin also affects the skin color. The word melatonin means ‘skin whitening’. Presence of melatonin causes skin darkening. It affects the skin in some animals. But it does not change the skin colour of humans. Some plants have small amounts of melatonin as well.

Melatonin synthesis

Melatonin is chemically N-acetyl-5-methoxytryptamine. It is made from amino acid tryptophan. Synthesis is primarily nocturnal or occurs at night. Melatonin synthesis is inhibited by exposure to light; production is stimulated during periods of darkness. Serum melatonin levels are highest prior to bedtime. Melatonin is synthesized in the pineal gland, retina, bone marrow, gastrointestinal tract, and bile.

Melatonin levels

While some persons are high secretors of this hormone who have peak night time melatonin levels between 54-75 pg/mL. On the other low secretors typically have peak night time levels in the range of 18-40 pg/mL.

Where is melatonin found and what does it do?

Melatonin, once secreted from the pineal gland, circulates in blood to reach all the parts of the body.

Melatonin helps in regulating the body’s internal clock. It maintains the cycles of sleep and wakefulness. Melatonin is also known to have anti-oxidant properties and has some role as a free-radical scavenger.

There have been studies that show it has anticancer, anti-aging and antidepressant properties as well. Some diseases have been shown to be associated with low levels of melatonin. These include coronary heart disease, multiple sclerosis, epilepsy, and postmenopausal osteoporosis.

To maintain the sleep cycle, the blood levels of melatonin start to rise about 2 hours before bed time. This sets the body in a ready state for sleep. For sleep, the body’s core temperature needs to be lowered slightly for example.

Medical uses of melatonin

Since melatonin is important in maintenance of sleep, it has been used in the treatment of insomnia. It can be used as sedative pills that make one sleepy. This is the most common use.

The second use is to reset the body’s internal clock. This is of vital importance in persons who suffer from jet lag. Jet lag occurs when a person travels across time zones. For cases of jet lag melatonin therapy at night is often combined with Bright Light Therapy. This helps normalize the sleep rhythms. This is also helpful in persons who need to work in shifts. Doses range from 0.3 to 8 mg.

Melatonin has also been tried in the treatment of depression and depressive illnesses. Melatonin has been shown to benefit in cancer as well. Various cancer types have been shown to be responsive to oral melatonin (10-50 mg daily). This includes breast cancer, non-small-cell lung cancer, metastatic renal cell carcinoma or kidney cancer, hepatocellular carcinoma (liver cancer), and brain metastases from solid tumors (spread of primary cancers to the brain. Melatonin has also shown beneficial effects in reducing blood cholesterols such as LDL cholesterol.

Reviewed by , BA Hons (Cantab)

Further Reading

Last Updated: Oct 8, 2014

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