Tuesday, October 09, 2007

On the Question, "How Much Sleep Does My Child Actually Need?"

From Po:

You might notice that in both of our sleep articles, we never come out and say, "here's how much sleep your kids needs - X hours." I don't think there's an easy answer to this, and I don't like pretending there's an easy answer when in fact it's complicated. Perhaps I'm most worry of the simple advice line, "your 5th grader needs 10 hours of sleep," because I don't think merely telling people this nugget will have any affect at all. I might as well be telling people "you need 5 million dollars to be financially secure." That isn't going to help them get from point A to point B - from where we are today, to where we need to be. So I emphasized, in the article, how every 15 minutes counts, and how a single hour can have dramatic consequences. I'm hoping the integrity of that science will push parents and children to find 15 minutes more, or a half hour more.

For the record, here's a simple chart we made which shows the gap between "what kids need" and "what they get." It uses data from Dr. Fred Danner at the University of Kentucky.

According to the sleep scientists, one of most-common incorrect assumptions is that you could draw a straight line from how much sleep your 6 year old needs to how much sleep an adult needs, and plot kids along that slope by age. I.e., as kids get older, they don't need as much sleep. While there's some slope from age 6 to age 12, the sleep scientists say that all teenagers, ages 12-18, really need 9.2 hours sleep. Their brains are still developing up until about the age of 21 (during later teen years, their brains appear to be pruning away unnecessary synaptic connections in the prefontal cortex, and this seems to improve their judgment of risk). At the end of puberty, the "phase shift" of delayed melatonin ceases.

How do the sleep scientists know that kids need 9.2 hours? Well, here they make a crucial assumption. They assume the body and brain will wake up when they've had all the sleep it needs. So they say teens "need" 9.2 hours by having experiments where the kids sleep a ton for weeks before coming into the sleep clinic - so they're entirely rested - and then letting them sleep all their bodies want in the clinic. The teens slept over 9 hours. In fact, at that point the researchers did wake up many of the kids.

So that might be how much the body wants, but is it fair to say that's what the body/brain really, truly needs? The scientists believe so. On the other hand, it's also fair to ask "at what point do we see a steep dropoff in performance, due to less sleep?" Is there a tipping point? The answer appears to be that we see minor consequences for only getting 8 hours sleep, but we see major consequences for only getting 7 hours sleep. One study of over 3,000 students in two school districts in Ontario, Canada demonstrated this dynamic. We didn't include this study in our New York article because the data is literally too hard to explain in just a few words, and you'll see why. Basically, they asked kids if they felt sleepy in the morning. 73% of the kids felt sleepy from 8 am to 10 am. They were performing worse than the "not sleepy" kids, but only slightly worse, nothing alarming. However, there was an additional subgroup who still felt very sleepy from 10am to noon. This group had real problems, from decreased grades to missing school and sports, etc. The rate of "sleep consequences" skyrocketed up 46% to 220%, depending on the variable. They were also getting less sleep - under 7.5 hours.

None of this can be taken as a rule and applied to individual kids. Some people need more, some need less. In sleep clinics there are children getting 11 or 12 hours sleep, yet it's still not enough. And we all have heard stories about a few uniquely driven adults who seem to thrive on 5 hours sleep.

One of the most interesting sub-analyses is being done by Dr. Oskar Jenni in Zurich. He has some preliminary data which, in a strange way, confounds the odds that students who get A's average 15 more minutes than the B's, who in turn average 15 more minutes than the C's. Despite those overall odds still holding true, Jenni has noticed that many very-gifted children actually need less sleep. He theorizes that smarter people actually can sleep less, because they have more efficient sleep systems. The more they sleep, the better it is for them - but they can do more with less, compared to others. (Note: this is very preliminary and untested. Please do not use it to justify letting your gifted child stay up late.)

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2 Comments:

Anonymous Simon said...

Thanks for a thoughtful response to a common question. is there any way that your sources could be referenced or at least the authors given so that I can read the original papers?

10:04 PM  
Blogger Ashley Merryman said...

Hi, Simon,

We don't automatically include specific citations because there's so much that we would need to cite, that it would make the blog virtually unreadable. Moreover, a lot of it is highly technical, so we're reluctant to suggest that to the casual reader. The National Sleep Foundation also is a good resource for quick overviews of the research if that's what you are looking for. For this post specifically, Fred Danner's work isn't yet published in a journal. He's presented at conferences, and he was kind enough to give us his presentations and speak with us several times. The Canadian study is Gibson, et al "Sleepiness is Serious In Adolescence..." BMC Public Health, 5/2/06.

9:06 AM  

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