Stop Taking Melatonin as a Sleep Aid, Say Sleep Doctors

Some years ago, pediatrician Dr. Judith Owens noticed a disturbing pattern. A professor of neurology at Harvard Medical School affiliated with Boston Children’s Hospital, many of her patients are children who have trouble sleeping. “I’ve been in practice for 40 years,” she says. “There has been a seismic change in the number of patients I see, particularly in sleep clinic, who are now on melatonin.” It is rare, now, for her to see a sleepless child whose parents have not at least tried giving them the hormone.

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It’s not just children. Between 1999 and 2018, the number of adults taking melatonin, which is available in the U.S. over the counter as a supplement, more than quintupled. It’s often marketed as a natural sleep aid—almost as if it were a vitamin. However, because it’s classified as a supplement, not a medicine, these claims don’t need to be evaluated by the U.S.Food and Drug Administration (nor are they). What’s more, “the American Academy of Sleep Medicine does not recommend melatonin for insomnia,” says Marie-Pierre St-Onge, director of the Center of Excellence for Sleep and Circadian Research at Columbia University.

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The effects of taking the hormone daily for long periods of time are not well-understood. In November, preliminary, unpublished results reported at the American Heart Association meeting found a connection in adults between taking melatonin for more than a year and heart failure. Although that study may be less informative about melatonin than about the link between heart disease and insomnia, it highlights the fact that there is relatively little known about using melatonin the way an increasing number of people are. 

It’s a gap that concerns many sleep doctors, including Owens. “It’s a hormone that has many powerful effects,” she says.

What melatonin does

In the evening, your body begins to produce melatonin, which is made primarily by the pineal gland. Melatonin levels peak in the early morning and taper down after sunrise. The hormone is thought to provide the body with a sense of how long the night is, to help synchronize biological processes with the sun.   

Once it’s floating around, however, melatonin affects more than sleep. Some decades ago, scientists were surprised to find that it tunes the immune system, increasing and decreasing different forms of inflammation. A lack of melatonin leads to increased fat accumulating in the livers of mice. There is evidence that tissues other than the pineal gland, including bone marrow, make their own melatonin, and the list of cell types with receptors allowing them to sense melatonin turns out to be immense. The hormone also appears to help direct the death of cells, so scientists are curious what role it might have in aging more generally.

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Careful studies of melatonin and its metabolites in people’s blood and urine have revealed that there are a number of disorders where its levels are disrupted, including depression, schizophrenia, bipolar disorder, Type 2 diabetes, and certain types of cancer. Some people with Alzheimer’s disease may have very little daily cycling of melatonin, perhaps contributing to the sleep difficulties that are a feature of the neurodegenerative disorder. 

Taking melatonin under a doctor’s advice can be helpful for people in these situations. Studies have shown, too, that blind people whose natural melatonin cycles get out of whack, leaving them with a form of constant jet lag, can benefit from supplementation. Children with autism can sometimes benefit from being prescribed melatonin, says Owens. It’s also been explored as a potential therapy after heart attacks, says Dr. Tom Scammell, a professor of neurology at Harvard Medical School and physician at Beth Israel Deaconess Medical Center.

How people are actually using melatonin

There is a big gap between how researchers and doctors think about melatonin and how many people are using it. To try to trace connections between long-term melatonin use and other health conditions, some researchers have turned to electronic health records. 

On November 3, an abstract from an American Heart Association meeting described an unpublished study using this type of data. It included some startling numbers: Over the course of five years, adults who were prescribed melatonin and took it for a year or more had a 90% greater risk of heart attack than people of a similar health status who didn’t take melatonin.

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“Melatonin supplements may not be as harmless as commonly assumed. If our study is confirmed, this could affect how doctors counsel patients about sleep aids,” said Dr. Ekenedilichukwu Nnadi, the study’s lead author and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care, in a statement.

However, it’s not necessarily the case that melatonin caused the heart failure documented in this study. In fact, points out Scammell, insomnia and heart disease often travel together, with 50% of people with heart failure having insomnia compared to 15% in the general population. 

So people who have insomnia and are given melatonin by their doctors in an attempt to cope may already be on the way to developing more serious heart problems. 

“It is possible that the poor sleep that triggered use of melatonin was an early sign of heart problems,” Scammell says.

More data needed

Still, the study is an attempt to get at the bigger question of what taking melatonin long-term does to the body. 

Does taking melatonin as a supplement interfere with the body’s own ability to make melatonin naturally? That’s still an open question, says Owens. But as a pediatrician, she is worried that kids who take melatonin regularly for months or even years may suffer long-term effects that may not become clear until later.

“Melatonin has effects on the immune system, on bone growth, on the reproductive system. That’s always been a big concern—whether it affects pubertal development,” she says. While short-term studies have not found an immediate effect, studies looking at the long term are lacking, she continues.

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Dr. Marcel Smits, a neurologist at Hospital Gelderse Vallei in the Netherlands, studies the use of melatonin in children with ADHD and other diagnoses. He and his colleagues found after an average of 3.7 years, these children, who took the medicine regularly at doses determined by doctors, did not show adverse effects.

But dosage must be precisely calculated in these cases, and patients should be monitored, he says. In adults and in children, taking too much melatonin can interfere with the body’s circadian rhythm, potentially worsening sleep or having other effects. What’s more, some people break melatonin down more slowly than others, and even a moderate dose can stick around in their bodies longer than you’d want, he says. 

In the U.K., melatonin is available only by prescription and is meant to be used for short periods under the care of a doctor. The fact that melatonin is easily available in the U.S. might encourage misuse, says St-Onge: “When it’s over the counter, people feel like it can’t hurt. If it can’t hurt, a lot could be better than a little.”  

“This is something we need to dig more into and really evaluate what it means to be taking melatonin for a long time,” she continues.

If you are having trouble sleeping, a better choice, St-Onge and Owens agree, is to try changing behavior around bedtime. Cognitive behavioral therapy for insomnia, or CBT-I, is the gold-standard treatment for sleeplessness in both children and adults. Studies show that this modification–which involves a number of stages designed to set you up for better sleep–has a longer lasting, better effect than any sleeping pill.  

Something to sleep on.