Author: Dr Eugene Tan, Dermatology Registrar, Hamilton, New Zealand, 2009.
Melatonin is a hormone. It is synthesized in the pineal gland of the brain. It is most well known for its effect on the regulation of our sleep-wake cycle over a 24-hour period, also known as the circadian rhythm.
The level of melatonin in the blood can vary 10-fold within a day reflecting the different degrees of secretion by the pineal gland. The lowest levels are during the day-time and highest levels are at midnight coinciding with its role in maintaining sleep. The level of melatonin in the blood also varies with age. The highest concentrations are from ages 1-5 and it declines after puberty so that the elderly have very low levels.
Melatonin is available as a medicine as tablets that range in dose from 1mg to 20mg. Although melatonin is a hormone, it is regulated differently in many countries. In New Zealand and the European Union, melatonin is a prescription-only product. In New Zealand, it is not yet registered by Medsafe or subsidised by PHARMAC, but melatonin is available under Section 29 for the alleviation of jet lag and management of insomnia. In the United States, melatonin is considered a dietary supplement and can be purchased without a prescription.
The normal role of melatonin in the body is not yet fully understood. Most of our current knowledge of melatonin has come from research in the last two decades. The first known effect of melatonin was that pineal glands from cows lighten the skin of frogs. Since then, melatonin has been shown to have more effects than just on the circadian rhythm.
Melatonin can act as an antioxidant. Supplementation of melatonin has been shown in small, uncontrolled studies to protect against heart disease, cancer and Alzheimer disease. However, the amount of melatonin needed to achieve these effects is extremely high (up to 100,000 times those of normal blood values). Long-term safety studies are not available and hence such large doses cannot be recommended at this stage.
Our blood pressure at night can be affected by melatonin. There is some evidence that low doses of melatonin at night can lower blood pressure.
Melatonin has been shown in some small studies to have an anti-cancer effect in patients with breast cancer, cervical cancer and metastatic melanoma.
Melatonin is commonly used to assist with sleep. It has been shown to improve the quality and duration of sleep. The dose used to induce sleep is 1 to 5 mg.
The effect of melatonin on the circadian rhythm has prompted its use by frequent travelers to treat/ prevent jet lag. To treat jet lag, a dose of 2-3 mg, 30 minutes before bedtime for up to four days after arrival is appropriate. To prevent jet lag, the dose needed is smaller: 0.3-0.5mg starting the day before departure is recommended.
At this moment in time, melatonin cannot be recommended for its antioxidant, anti-cancer or blood pressure lowering effects.
As this hormone affects the sleep-wake cycle, the most common side effect is daytime sleepiness. Other side effects include dizziness, headache and loss of appetite.
The wool industries in New Zealand and Australia have undertaken a great deal of research on melatonin. Numerous animal studies show that it stimulates hair growth in fur-producing animals and assists in the process of moulting, i.e. the change from the winter coat to summer fur.
Given its effect on hair in animals, melatonin has been investigated for its effects on treating alopecia (hair loss) in humans. When applied as a lotion, melatonin has been shown in one trial to increase hair growth in women with diffuse alopecia or androgenetic alopecia.1 The trial has not subsequently been repeated and firm recommendations on the use of melatonin for alopecia cannot be made at present.
As melatonin can lighten the skin of amphibians such as frogs, the same effect was assessed in humans. Melatonin supplementation in 7 individuals for 18 months did not affect skin pigmentation. 2
Our understanding of melatonin has increased significantly over the last two decades. Melatonin plays a significant role in the regulation of the circadian rhythm and a big role in the regulation of hair growth in animals. In humans, good evidence exists for its effects on sleep and treatment of jet lag. The use of melatonin in dermatology still remains to be fully investigated.
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