Melatonin is certainly an interesting substance. It began to pique the curiosity of researchers in the 1950s when they discovered that production of this hormone by the pineal gland in the brain declined with age. In spite of the fact that a wealth of information has been gathered about melatonin since that time, no consensus about its potential use as a dietary supplement has emerged. There is certainly no shortage of claims made on behalf of this compound. According to proponents it can improve sleep, deal with jet lag, induce serenity, boost the immune system, reduce the risk of heart disease and cancer, enhance one’s sex life and prolong life expectancy.
Aside from a possible beneficial effect on sleep and jet lag, there is not much evidence to support the claims. Some of the claims are bizarre indeed. The “serenity” connection is based on a tradition practised by some yogis. Not a particularly appealing one. They drink urine in the morning to make meditation easier. Some melatonin proponents try to justify this action by linking it to the high melatonin content of morning urine. Drinking urine, which while distasteful is not generally risky, may convince the body it has had extra sleep.
The life expectancy data is not quite as quirky but comes totally from rodents, which are not very good models for human reaction to melatonin. Critics have pointed out that the “landmark” study which found that longevity in mice could be increased with a transplant of pineal tissue from younger animals was flawed because the mice were of a genetic variety which produces no melatonin by itself. Perhaps we should not be surprised by the sleep connection, given that melatonin is produced mostly during the night and its secretion is impaired by exposure to bright light. It has appropriately been termed the “Dracula hormone.” Melatonin does seem to be related to the circadian (from “circa” around and “dian” day) cycle of our body and therefore can benefit “jet lag.” This condition induces drowsiness, irregular sleeping rhythms and moodiness in people changing time zones or working shift hours. But the dosage required and the appropriate regimen for taking melatonin pills is unclear.
As far as inducing sleep, studies have suggested that as little as 0.3 mg of melatonin can induce drowsiness and that the 3.0 mg dose available in commercial pills is more than needed. Again, there is no consistent evidence that melatonin is an effective sleep-inducing agent. Another consideration is that these supplements may not actually contain what the label claims. In the US melatonin is sold as a “dietary supplement” and is therefore not subject to the same kind of strict regulations as drugs are. Its sale in Canada without a prescription is prohibited due to concern about melatonin’s hormonal properties.
These properties have in rare cases caused problems. A man who developed enlarged breasts and a low sperm count was ready to undergo breast reduction surgery and stopped taking melatonin in preparation for the operation. It never had to be carried out because the problem resolved when he gave up the melatonin. On the other hand, it is the compound’s hormonal effect that may be responsible for the putative benefits. Several studies have suggested that blind women have a significantly reduced risk of breast cancer. They also have high levels of circulating melatonin. Of course this does not mean that melatonin is responsible for the reduction in risk, but there may be a connection.
Laboratory evidence indicates that melatonin can suppress the growth of mammary tumors, probably by interfering with estrogen receptors in cells. Estrogen is well known to stimulate some breast cancers. A few researchers go as far as suggesting that modern life with its bright lights and fewer hours of sleep can be linked with an increase in breast cancer rates. Lights may not be the only problem. Electromagnetic fields, perhaps even those generated by household appliances, may reduce melatonin production by the pineal gland. Add to this the fact that melatonin is an effective free radical scavenger, and that free radicals are associated with cancer, and we may indeed be looking at a substance that is useful in the prevention and treatment of the dreaded disease. But before we can make any specific recommendations, we need to replace the melatonin hype with human clinical trials. Until that happens, we will remain in the dark about the "darkness hormone."
