Melatonin is a natural hormone produced by the pineal gland. Melatonin supplements are effective at treating sleep disorders. In addition, melatonin is used to boost the immune system, reduce the risk of cardiovascular disease and protect against carcinogenic DNA damage, and is also an adjunct treatment for cancer.
Together with the hypothalamus, the pineal gland - also known as the epiphysis cerebri - controls the wake/sleep cycle. In conditions of darkness, it releases melatonin, the hormone which regulates our internal body clock in terms of sleep. Melatonin levels peak between one and five in the morning but as day breaks, the appearance of light inhibits its secretion and the body’s internal clock gets ready to wake us up. Levels of melatonin also increase after a meal which partly explains post-prandial drowsiness.
Once released, melatonin only remains in the bloodstream for between 20 and 90 minutes. As it is highly fat-soluble and somewhat water-soluble, melatonin easily penetrates all the body’s cellular compartments (membrane, cytoplasm and nucleus).
As with many other hormones that play a crucial role in our health, melatonin production starts to decline from puberty, continuing to fall so that by the age of 70, it can represent just 10% of youthful levels. Often, this decrease in melatonin production also signals the onset of a number of degenerative diseases.
An exceptionally powerful antioxidant
Melatonin is one of the most powerful known antioxidants. It has all-round, direct and indirect antioxidant effects and is a free radical scavenger. As well as neutralising a wide range of highly reactive molecules, melatonin also stimulates antioxidant enzymes. In addition, a by-product of the interaction between melatonin and free radicals, N1-acetyl-N2-formyl-5-methoxykynuramine, is itself a powerful free radical neutraliser, with at least the same potency as melatonin itself. This ability to induce an ‘antioxidant cascade’ further increases the protection melatonin confers against oxidative damage.
Ageing, melatonin and sleep disorders
Older people often experience insomnia, largely because melatonin production, like that of many other essential hormones, declines with age. Sleep problems such as waking in the night, or too early in the morning, become more frequent.
Researchers at the Technion Israel Institute of Technology studied the effects of melatonin supplementation on elderly, melatonin-deficient subjects suffering from insomnia. For one week, they were given either 2mg of fast-release melatonin, 2mg of slow-release melatonin or a placebo two hours before going to bed, followed by a 2-month period of either 1mg of slow-release melatonin or a placebo 2 hours before bedtime.
Treatment with 2mg of fast- or slow-release melatonin was shown to improve the participants’ sleep. They fell asleep more quickly when taking the fast-release melatonin, while quality of sleep was better with the slow-release supplement. These improvements were said to have continued when the subjects switched to supplementing with 1mg melatonin but declined once treatment had stopped1
Preventing jet lag
We experience jet lag when the body clock is disrupted during medium- or long-distance travel. It can take a whole day per time zone crossed for the body to readjust and find its normal rhythm. Melatonin has been widely used since 1994 by travellers and airline staff to combat jet lag.
The circadian rhythm, characterised by the rise and fall of hormone levels and the sleep/wake cycle, is linked to the rising and setting of the sun. Most methods designed to reduce the effects of jet lag are based on this connection and on the fact that the effects of the day/night cycle are induced by melatonin.
Strategies for influencing the sleep/wake cycle, including those used to relieve the symptoms of jet lag, are centred on the manipulation of exposure to light and on taking melatonin supplements at key times.
UK researchers reviewed 10 clinical trials that used bright light, either on its own or combined with melatonin, to try and accelerate the re-establishment of the circadian cycle following simulated or actual flights crossing more than 5 time zones 2
Eight of the ten trials showed that melatonin produced a clear reduction in jet lag. The researchers concluded that 2mg to 5mg of melatonin taken at bedtime at the destination is an effective way of minimising the effects of jet lag. For maximum efficacy, melatonin supplementation should continue for 2 to 4 days. In addition, attention should be paid to mealtimes and to exposure to light; both can accelerate the restoration of the circadian rhythm but eating at the wrong time, consuming too much alcohol or coffee and ill-timed exposure to bright light will all slow it down.
Melatonin and Alzheimer’s disease
It seems that melatonin may relieve certain symptoms related to Alzheimer’s disease. Problems with the sleep/wake cycle are characteristic of this disease, as is a phenomenon called ‘sundowning’, which sometimes manifests in agitation and aggression. It is a behavioural problem that is particularly prevalent when Alzheimer’s is accompanied by depression. It manifests as an exacerbation of various cognitive and behavioural symptoms during the evening hours. While its causes are not yet clearly understood, many researchers believe it could be linked to a decline in melatonin levels3
Scientists at the Netherlands Institute for Brain Research in Amsterdam have explained how the age-related decline in melatonin production may not only influence circadian rhythms but may also play a role in the development and characteristics of Alzheimer’s disease.
They point to research which shows that ageing is accompanied by a progressive deterioration in circadian rhythms, due partly to degenerative changes in the suprachiasmatic nucleus and in the pineal gland which result in decreased melatonin production. They also cite studies demonstrating that in Alzheimer’s patients the body clock is severely disrupted and that there is a link between the degree to which melatonin secretion declines and the severity of the mental problems caused by the disease. They state that “patients with disturbed sleep/wake cycles have problems with the rhythm of melatonin secretion and the disappearance of the daily melatonin rhythm in Alzheimer’s patients is consistent with clinical disorders of this rhythm such as delirium, agitation and sleep/wake problems”.
Sedatives such as benzodiazepines and anti-psychotics such as haloperidol are prescribed to relieve the ‘sundowning’ syndrome or sleep problems in Alzheimer’s patients, but they are not very successful and can sometimes even exacerbate the problems. Melatonin supplements on the other hand, seem to offer a better alternative since they treat the cause: a deficiency in melatonin production.
Open-label and controlled studies suggest that melatonin administration results in a significant reduction in cognitive decline in Alzheimer’s patients. Such benefits may be due in part to melatonin’s ability to induce slow wave sleep in elderly people and to increase sleep’s restorative phases. In addition, melatonin protects neurons against beta-amyloid toxicity and the development of amyloid plaques associated with Alzheimer’s disease 4
Animal and human cell studies have shown that melatonin has significant anti-cancer properties. It can directly destroy various types of human tumour cells and inhibit the growth rate of existing tumours. Melatonin has a natural oncostatic action which has an inhibitory effect on the growth of cancer cells. It can delay a tumour’s development and metabolism by lowering body temperature. An antioxidant-stimulator and antioxidant in its own right, melatonin prevents tumours from causing radical damage to normal cells and as a consequence, restricts oxidative damage to DNA, lipids, amino acids and proteins.
Adjunct cancer treatment
Numerous clinical studies have investigated melatonin in cancer treatment - either on its own or combined with other substance. It appears to boost the efficacy of other anti-cancer treatments, reduce their side-effects, increase survival rates and improve patients’ quality of life.
When used alongside conventional cancer treatments, melatonin seems able to inhibit the proliferation of certain cancer cells and may help combat the toxic side-effects of chemotherapy and radiotherapy.
A literature review identified almost 100 human studies, 50 of which were evaluating melatonin as an adjunct cancer treatment, and the others, levels of endogenous melatonin in cancer patients.
A meta-analysis of 10 reports published between 1992 and 2003 examined the results from randomised, placebo-controlled studies conducted by Italian and Polish researchers, involving patients with tumours treated with melatonin combined with another treatment. The researchers noted a significant improvement in survival at one year from all doses of melatonin when given as an adjunct treatment in various advanced cancers. Compared with those not given the melatonin, treated patients had a 44% lower risk of death in the year following their enrolment in the study 5
Increased lifespan in mice
Mice were given 10mcg/ml of melatonin in their drinking water each evening. At the start of the study, they were aged 575 days. Not only did the maximum lifespan of the mice increase by 20% but they also exhibited several markers of more youthful animals, such as more luxuriant fur, increased vigour and activity and better posture 6
. A second study on a different mouse species produced similar results7
1. Melatonin replacement therapy in elderly insomniacs, 1995, 18(7); 598-603.
2. Herxheimer A. et al., Melatonin for the prevention and treatment of jet lag, Cochrane Database Syst. Rev., 2002, (2): CD001520.
3. Wu Y.H. et al., The human pineal gland and melatonin in aging and Alzheimer disease, J. Pineal Res., 2004 Dec 21 (online pub date).
4. Cardinali D.P. et al., Clinical perspectives for the use of melatonin as a chronobiotic and cytoprotective agent, Ann. NY Acad. Sci., 2005 Dec, 1057: 327-36.
5. Melatonin in the treatment of cancer: a systematic review of randomized controlled trials and meta-analysis, 20th Annual Meeting of the American Association of Naturopathic Physicians, August 24 through 26 2005, Phoenix, Arizona.
6. Maestroni G.H.M. et al., Pineal melatonin, its fundamental role in aging and cancer, in: Neuroimmunomodulation: interventions in aging and cancer, Annals of the NY Academy of Sciences, 1988, 521: 140-148.
7. Maestroni G.H.M. et al., Melatonin, stress and the immune system, Pineal Research Review, 1989, 7: 203-26.