The human body is biologically attuned to the environment in such a way that it responds with what might be considered "biological attitudes" in a manner of speaking. The study of sleep cycles from one person to another and the differences between them—let alone the differences between those of children and those of adults—is a fascinating, bio-anthropological study to say the least. At least, that's how some researchers feel, but the truth about sleep isn't necessarily something many people would want to tell their children because they may never live it down.
"Research on American kids suggests that 'bedtime resistance'—that fist-in-the-air struggle against the oppressive forces of lights-out via tantrums, conveniently timed bathroom breaks and the need to ask right now about where babies come from—is common and increases as children age," jests Maggie Koerth-Baker, senior science writer for FiveThirtyEight as she broaches the topic of the latest research on the subject of the biological clock. "The New York Longitudinal Study, which lasted from 1956 to 1988, found that 26 percent of 2-year-olds exhibited bedtime resistance behaviors, and that figure rose to 50 percent by the time kids were 5.
"But kids whose behavior was documented in similar longitudinal research in Switzerland weren't as rebellious. A 2005 study using that data found that, for them, bedtime resistance peaked between 2 and 4 years old, at around 18 percent. And rates of youthful rebellion changed as parental behavior changed. The 2005 study also found that bedtime resistance had been decreasing over time. The peak for kids born in 1974-78 was about 30 percent prevalence at age 5. Meanwhile, resistance among kids born in 1986-93 at age 3, closer to 10 percent."
The authors of the aforementioned studies found that Swiss parents gradually transitioned to increasingly later bedtimes. All this did was yield less frustration for everyone with little to no observable health consequences. Now, of course, children have to get a good night's rest, and in general, their bodies tend to exemplify a proclivity for sleeping longer hours than their adult counterparts anyway; however, what constitutes a "good night's rest" from one person to another can be very different, and in children, it is exceptionally variable.
"What constitutes normal, healthy sleep changes between individuals, and kids are even more variable than adults, said Oskar Jenni, a researcher at the child Development Center of the University Children's Hospital Zurich in Switzerland. That fact often clashes with the reality that bedtimes are sociocultural decisions based, at least in part, on parents' expectations of how long kids should sleep. Scientists are still trying to understand how culture and biology work together to create our sleeping lives, and they are learning that cultural variables can have a big impact on outcomes of sleep that we might be tempted to view as purely biological: how easily we fall asleep, how we feel the next day and even what it means to 'get enough,'" Koerth-Baker writes.
Kate Bartel, a recent PhD graduate from Flinders University in Australia under the auspices of Michael Gradisar and his sleep science library, said that the biggest determinant when it comes to sleep is biology itself. By this she means that the body responds to light in such a way that it triggers sophisticated sleep cycles and shifts in behavior.
"The suprachiasmatic nucleus, or SCN, a tiny area of the brain near the optic nerves, uses the light picked up by your eyes to calibrate itself as a timekeeping device for your body," says Koerth-Baker. "Electrochemical impulses produced by the SCN help to control a wide range of bodily functions, including when you get hungry, how much of what you eat turns into fat and whether your skin is ready to protect itself from sun exposure—processes that are commonly referred to as the circadian rhythm."
These are the signals from the SCN that inform you regarding when to sleep using the aforementioned triggers, especially melatonin production. Melatonin is a hormone that does a lot of different things, but it also deliberately fatigues people so as to prioritize sleep in human behavior. As such, when the sun goes down and takes its bright light with it, melatonin is what orients the mind toward the concept of bedtime.
"But how we sleep—and how we experience the quality of the sleep we get—isn't driven purely by biology. There's a cultural aspect to this as well, and you can see it in some disorders of the circadian rhythm, like delayed sleep-wake phase disorder," said Koerth-Baker. Bartel fed her this point and said that many who have sleep-wake phase disorder are unable to fall asleep even deep into the night and after midnight. In some cases, these struggles can persist as late as 5 a.m. when the sun is beginning to rise again already to some extent, burgeoning on the horizon and mitigating the darkness of the sky to a dark blue at the very least.
Bartel explained that many in this situation get therapy and aim to alter their rhythm using behavioral adjustments, light exposure and hormones. This kind of therapy doesn't work for everyone, though, which simply goes to show the hardship of trying to overcome the body's natural inclinations in this regard.