Melatonin supplements are often taken as a sleep aid, although it’s not clear if or how they work. Our bodies also make melatonin naturally, and a new study with zebrafish suggests that even in the absence of a supplement, naturally occurring melatonin may help us fall and stay asleep.
“When we first tell people that we’re testing whether melatonin is involved in sleep, the response is often, ‘Don’t we already know that?’” says David Prober, an assistant professor of biology at the California Institute of Technology (Caltech). “This is a reasonable response based on articles in newspapers and melatonin products available on the Internet.
“However, while some scientific studies show that supplemental melatonin can help to promote sleep, many studies failed to observe this, so the effectiveness of melatonin supplements is controversial. More importantly, these studies don’t tell you anything about what naturally occurring melatonin normally does in the body.”
There are several factors at play when you are starting to feel tired.
Sleep is thought to be regulated by two mechanisms: a homeostatic mechanism, which responds to the body’s internal cues for sleep, and a circadian mechanism that responds to external cues such as darkness and light, signaling appropriate times for sleep and wakefulness.
For years, researchers have known that melatonin production is regulated by the circadian clock, and that animals produce more of the hormone at night than they do during the day. However, this fact alone is not enough to prove that melatonin promotes sleep. For example, although nocturnal animals sleep during the day and are active at night, they also produce the most melatonin at night.
In the hopes of determining, once and for all, what role the hormone actually plays in sleep, Prober and his team at Caltech designed an experiment using the larvae of zebrafish, an organism commonly used in research studies because of its small size and well-characterized genome. Like humans, zebrafish are also diurnal — awake during the day and asleep at night — and produce melatonin at night.
They found that fish with the mutation slept only half as long as normal fish. And although a normal zebrafish begins to fall asleep about 10 minutes after “lights out” — about the same amount of time it takes a human to fall asleep — it took the aanat2 mutant fish about twice as long.
The study was published online in the journal Neuron.
“This result was surprising because it suggests that almost half of the sleep that the larvae are getting at night is due to the effects of melatonin,” Prober says. “That suggests that melatonin normally plays an important role in sleep and that you need this natural melatonin both to fall asleep and to stay asleep.”
