The Secret Life of Melatonin

Melatonin is a powerful hormone with some surprising effects in the body.

Posted Jul 05, 2015

Melatonin is a common sleep remedy that can be found in almost any pharmacy or grocery store. Some books and websites have embued melatonin with nearly magical properties as an anti-oxidant, anti-aging miracle chemical, but what do we really know about melatonin, and how can we use that knowledge safely to improve both sleep and health?

Melatonin was first isolated in 1958 from a brain region called the pineal gland, and it was found to play a major role in the body’s circadian rhythms. It promotes sleep as levels climb in response to darkness. Amounts fall during the day, and levels also vary from a low in the summer to highest in the winter.

At large doses (even the 3mg dose pills are at least 5-6X natural levels), melatonin can be mildly sedating, but its real appeal is in helping establish the circadian rhythm better. People with jet lag or shift work can take a small dose a little before bedtime and reestablish a better sleep cycle based on the time you have to be up and about, not necessarily the times your body thinks it needs to sleep based on being uprooted from another time zone. It’s also effective to help maintain the circadian rhythm for people with certain kinds of blindness. For short-term use in adults, it is hard to think of a sleep aid that is safer or better tolerated than melatonin. Most studies show a small amount of side effects including sedation, lightheadedness, or nausea. These are minor compared to the dry mouth, urinary retention, fuzzy thinking, and drowsiness caused by most other over-the-counter sleep aids.

However, melatonin is increasingly being utilized as a sleep aid for children, particularly those teenagers who stay up until 2 a.m. and can’t get out of bed for school, or for kids with ADHD or other conditions where insomnia is a frequent co-morbid condition. Doses as high as 10mg are sold, which is far, far higher than any natural amount of this hormone. It’s important to understand that there is way more to melatonin than just its sleep-promoting circadian rhythm properties. Melatonin is also part of a complex fertility and puberty-signaling cycle in the body. 

In many mammals, high melatonin levels suppress fertility in the winter, and when levels drop, the springtime fertility cycle begins. In fact, melatonin was investigated as a contraceptive in the 1990s and is commonly used in certain livestock to control fertility. 

While primates such as humans don’t have a winter infertile season, it does make one pause when contemplating taking large doses every night in an ongoing fashion. Melatonin levels that are good for a chipmunk in winter might not be good for the teenager starting puberty.

Young children have higher levels of melatonin than adolescents (one of the main reasons teenagers are night owls but little kids seldom are), and there are cases of children who develop brain tumors that destroy the pineal gland that makes melatonin who go into very early puberty. Since the tumors secrete other hormones, the absence of melatonin by itself may not bring on puberty, nor may super high levels (such as those a child would get from taking nightly melatonin) necessarily delay puberty. The problem is, we really don't know what melatonin does in humans around puberty.

Given that melatonin is a natural fertility suppressant, surprisingly, when used experimentally in women and men undergoing fertility treatments such as IVF, it has been shown to improve the viability of the embryos and the quality of the sperm, and low doses of melatonin can bring on an early fertility cycle in sheep. Melatonin’s antioxidant properties rather than the hormonal suppressing properties may be key here, particularly in women undergoing IVF who are also getting other strong hormonal treatments via shots. The complexity of the literature and the recent discoveries that melatonin is made in many places in the body, not just the pineal gland, tells us that melatonin is an important and powerful hormone that we don’t fully understand. Low levels may promote one fertility state while high levels another.

It may be that melatonin is a boon for people with stressed-out lives, tons of artificial light, and crazy sleep cycles but not so great for a kid with an insomnia problem. No human studies have shown that melatonin delays puberty, but the only long-term studies are small, didn’t test hormone levels, and were mostly in children too young to go through puberty. In primates and other mammals, high and low doses of melatonin have changed puberty onset and not always in the direction you might think. Studies showed very low dose melatonin (about 100th the amount a child would get from a 3mg dose) in primates advanced puberty by five months but delayed puberty in female cats.

As one author wrote: “Considering the pronounced effects of the pineal gland and melatonin on reproductive physiology in these nonhuman mammals, to assume they would not have some sexual effects in humans would … seem naive.” In fact, the National Institutes of Health recommends that melatonin should not be used in children as it is possibly unsafe. 

In summary, melatonin is a safe and effective short-term treatment for jet lag and shift workers who want to get sleep rhythms back in shape faster. In general, a very low dose (0.5-1 mg, for example), is more than sufficient. Other rare cases of people who have no pineal glands or who have permanent conditions such as retinal blindness may be better off on chronic low-dose melatonin given the benefits of established regular sleep cycles. For now, avoid use in children until more research about the effect on puberty and hormones is done.

Copyright Emily Deans, M.D.