What time do you go to bed at night? I don’t know your personal schedule. You might be an early riser or a night owl. But chances are, you let your brain chemistry be the guide. When researchers have monitored American adults, they’ve found that people go to sleep approximately two hours after their brains start to make extra melatonin, the hormone of drowsiness.
Two hours. That might mean your body starts feeling a rise in melatonin at 9:00pm, but you aren’t sleepy yet. So you go about your business, try to unwind, and then, finally, as melatonin levels keep increasing, you go to bed at 11pm.
But what about kids? Monique LeBourgeois wanted to know, so she and her colleagues fitted 45 healthy toddlers with wrist actigraphs – little bracelets that provide a continuous record of wakeful and sleep states. The researchers also asked parents to keep sleep diaries, noting when kids went to bed and when they woke up in the morning. And most importantly, LeBourgeois and colleagues devoted a day to collecting melatonin samples from the children. Starting in the afternoon, researchers hung out with families in their homes, taking saliva samples from the children every 30 minutes until one hour past the kids’ normal bedtimes.
The results were eye-opening. The average onset of the evening surge in melatonin, or “dim light melatonin onset” (DLMO), happened around 7:30pm, but kids didn’t go to bed two hours later. Instead, their average bedtime (lights out) was 8:15 pm, and – guess what – they didn’t go right to sleep. According to the actigraphs and sleep diaries, the average time of sleep onset was approximately 30 minutes later.
So the average kid was put to bed with the lights turned out just 45 minutes after his DLMO, and didn’t fall asleep for another half hour. Is this good? I don’t know. Sleep doctors often say that healthy people should be able to fall asleep within 20 minutes of putting their heads down. When it takes longer, we’re at risk for sleep problems: We may come to associate being in bed with feeling alert, and develop a kind of learned insomnia. According to this research, the average kid may be going to bed a bit too early.
And if that’s true, what about all the kids who go to bed earlier than average? Or the kids who have later-than-normal DLMOs? Some of the kids in this study took more than 90 minutes to fall asleep, and they were usually the kids with the earliest bedtimes. In fact, LeBourgeois and colleagues found that 1 in 5 kids were sent to bed before their evening melatonin surge had even begun. Imagine what that would be like – being asked to lie in bed while your brain thinks it’s time to party. No wonder if many kids resist bedtime.
Curious if these mismatched bedtimes were an important cause of sleep trouble, LeBourgeois led a follow-up study. Her team confirmed that kids whose melatonin surged later in the evening took longer to fall asleep after lights out, but it also depended on bedtime. The earlier kids were put to bed relative to their DLMOs, the longer it took them to sleep and the more they fought going to bed.
What do we make of this? The researchers suspect that many family bedtime struggles are driven not by the parents’ inability to enforce limits, but by a simple mistake: Parents are expecting kids to fall asleep before their children are biologically capable of doing so. Readjust expectations, and you might solve the problem.
But wait, I hear people ask. What about sleep requirements? If a preschooler has to wake up early, she needs to go to bed early, right? In many families, people are compelled by work and school schedules to wake up before their biological clocks are ready. What should they do?
There are no easy solutions, I’m afraid. But the research conducted by LeBourgeois and her team highlights an important point: Ignoring biology and sending alert kids to bed isn’t the answer. What makes more sense, I think, is to try to give biology a nudge, gradually, by reprogramming your child’s inner clock. Experiments suggest that exposing people to bright light early in the morning (between 6 and 8 am) helps change their circadian rhythms, making the melatonin surge happen earlier in the evening. And steering clear of counter-productive stimulants in the evening – like artificial lights, exercise, negative emotions, and too much excitement – is also crucial.