A good night’s sleep is crucial for all of us, but especially for children. My Alex is now 17 months old and is pretty good with his routine, being put to bed at 8 pm and usually waking up around 7:30 am. Along with a nap or two, he easily gets his recommended 12 hours a day of sleep. But our upstairs neighbors’ toddlers are bouncing on our ceilings until at least 10 pm most nights. Many Chinese parents tell me their child goes to bed at 9, 10 or even 11 pm — much later than the typical children of my expat and American colleagues. What explains this cultural difference, but more importantly — is either one healthier for a child?

One study from 2005 confirmed my personal observations that Chinese children not only go to sleep later than American children, they also wake up earlier. This comparative survey showed that Chinese children in elementary school sleep a full hour less than American children (9.25 vs. 10.2 hours); more worrisome were the Chinese children’s complaints of daytime sleepiness.

The main issue isn’t so much what time your child goes to bed: more importantly is their total amount of daily sleep, including naps (which very few children over five years take). Sleep research has shown that preschool-aged children need 11-12 hours, while school-aged children need at least 10 hours, and teens need 9-10 (infants need 16-18, and adults need 7-8). If your five year old is going to bed at 9:30 and waking up at 6:30 and already no longer takes naps, then their 9 hours a day of daily sleep isn’t enough for their long term health.

One of the main problems with insufficient sleep is the daytime sleepiness, an obvious consequence of not sleeping enough. A fascinating series of tests in children in China just published this year showed that insufficient sleep and daytime sleepiness both lead to worse school performance. Most of these children went to bed at 9-9:30 am and almost all got up at 7 am, causing a daily sleep debt of 1/2-1 hour for many children. While that may seem like a small amount, like any debt, it must be paid back, and most children cannot recover all of this lost time by sleeping late on weekends. Over time, this cumulative sleep deficit causes problems with attention spans, motivation, and also achievements on tests. Researchers hypothesize that the brain’s prefrontal cortex, which processes attention, creative processing, motivation, and abstract reasoning, is especially vulnerable to poor sleep. They conclude that “our results provide a cautionary tale for the practice in Chinese society that children spend a lot of time on studies even with the sacrifice of sleep time.”

One good bit of news from the same study describes how delaying school start times even by just a half hour can significantly improve sleep duration and daytime sleepiness. In their interventional study with six primary schools in Shanghai, delaying school openings from 7:30 to 8 or 8:30 gave the children almost an hour of extra sleep — and more importantly, less complaints of daytime sleepiness. This fits with studies in other parts of the world and supports the growing movement, led by pediatricians, to delay school opening times to 8:30 am. Just doing this could allow better sleep and improved test scores for all students!

Besides school performance, poor sleep also leads to an increased risk of overweight and obesity in children (as well as adults). A 2007 meta-analysis of 36 studies across the world showed a strong, independent association between short sleep duration and weight gain in children, which continues into adulthood. One study of 500 adolescent twins in Anhui, China showed an association between less sleep and more weight gain. Another survey of over 4,000 children in rural northeast China found that obese children were more likely to have insufficient sleep (less than 7.5 hours, including naps). While this isn’t a cause-and-effect, the association certainly is worrisome. There may actually be a physiological base to this, as research shows that inadequate sleep causes changes in the hormones which control appetite. Less sleep leads to less leptin and more grehlin, which increases our instinctive hunger reflex. Since the obesity rate in Chinese children is rising alarmingly, I think all parents at least should consider proper sleep in this context.

I can’t control the noisy kids upstairs, but in my own home I’m happy that we’ve taught Alex good sleep patterns, and we have plenty of leeway for 8:30 or 9 pm times if needed, all the way until his teen years. And when we choose schools we would definitely consider later start times as a positive factor.