美国国家公共电台 NPR Body Clock Blues? Time Change Is Tough. Here's How To Sleep Well Tonight（在线收听）

ALLISON AUBREY, HOST:

You know the downside of not getting enough sleep? Let me tell you it is a scary long list. I'm a health reporter, and every week, I see a new study. Lack of sleep - it's linked to anxiety, depression, weight gain, Type 2 diabetes, even certain kinds of cancer.

MATTHEW WALKER: If you understood the damage that insufficient sleep has on the brain and the body as I do, you would choose to do nothing else. It's purely a selfish act on my behalf that I give myself that eight-hour sleep.

AUBREY: That is sleep guru Matthew Walker. He's a sleep researcher at UC Berkeley and the author of "Why We Sleep." He has made it his mission to convince the world that sleep is important.

What is it that you've found over the years that really gets people's attention?

WALKER: I think it's different facts for different populations. You know, for example, sometimes, I'll go and speak to a lot of Fortune 500 companies where there is a large dominance of sort of Type A males in the audience. One of the first things I usually say in those speeches is regarding testicles - that men who sleep five to six hours a night have significantly smaller testicles than those...

AUBREY: (Laughter).

WALKER: ...Who sleep seven hours or more. In addition...

AUBREY: Oh, I'm sure that gets their attention.

WALKER: Yeah. It's the best opening that I've found yet. Testicles is probably one of the best hooks for maintaining people's attention.

AUBREY: (Laughter) Yeah. Hook them with small testicles.

WALKER: Yep.

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AUBREY: So clearly, all kinds of things can happen to you if you don't get enough sleep. But scientists have also learned a lot about how to get those eight hours in and how to improve the quality of our sleep. And it turns out that process starts from the moment you wake up.

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AUBREY: This is your NPR LIFE KIT for getting better sleep. I'm Allison Aubrey. I cover health and wellness here at NPR. And in this episode, we've got five things for you to do today to help you sleep better tonight.

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AUBREY: There is plenty to be said about good nighttime routines for bed. But in this episode, we will focus on how your daytime habits influence your sleep. One thing you need to know is you may not feel tired until 9 or 10 o'clock tonight, but your body started to prepare for sleep first thing this morning.

WALKER: From the moment that everyone woke up this morning that's listening to this, a chemical started building up in your brain. And that chemical is called adenosine, and it is the sleepiness chemical. And the longer that you're awake, the more of that sleepiness chemical builds up in the brain. And after about 16 hours of being awake, there should be enough of that healthy sleepiness sort of swilling around within your brain - enough of what we call sleep pressure - to then make you feel ready to fall asleep and then stay asleep for eight hours.

AUBREY: Is it really that direct? Is there really this compound that says, you are drowsy now?

WALKER: There is.

AUBREY: My biology is telling me to go to sleep.

WALKER: Yeah. And it's during that eight hours of sleep that the brain then starts to clear away and remove all of that adenosine, all of that sleepiness chemical.

AUBREY: And now you're ready to wake up. But here's the problem. In our society where it's go, go, go 24/7, lots of us override our internal body clocks. We just ignore these signals to sleep. What do I mean? Well, let's walk through a typical day.

So let's say it's morning. The sun is shining. But where are you? Many of us start our day in our dark bedrooms. Then we stop by a dark coffee shop. Then we get into our indoor cubicles, where there's no natural light. So what's missing?

WALKER: Daylight is perhaps one of the most powerful resetters of our 24-hour clock. So we need things like daylight just to keep us regular, to keep the precision of our 24-hour clock bang on the money.

AUBREY: So go ahead - pull open those curtains. Or better yet, go outside because natural light is the best kind of light.

WALKER: When daylight floods into the brain, it tends to put the brakes on a hormone called melatonin. And melatonin is the darkness hormone. It's the hormone that circulates in your brain and your body and, like a chemical bullhorn, shouts out to all of the cells of your brain and your body, it's nighttime. You should be asleep. But when daylight comes through the eyes, it actually turns the faucet off on melatonin. So there's no more melatonin being released. So your brain now realizes, oh, it must be daytime.

AUBREY: It's time to wake up.

So how much light do you really need in the morning?

WALKER: Try to make sure to get outside for at least 20 minutes during the early- to mid-morning hours to infuse your brain with daylight. These data in these scientific studies are now well-replicated that having daylight exposure in the morning tends to lead to better sleep in the evening.

AUBREY: OK. So your next habit to reconsider - caffeine. If you're like me, you get to the office. You have a cup of coffee, maybe another one. Here at NPR, it's free. It is super popular. And certainly, that cup of coffee at 10 a.m. - it can't really interfere with my sleep tonight, right?

WALKER: So I think people misunderstand caffeine and how it works with sleep. The way caffeine works is that it enters your system, and it latches onto the receptors of adenosine. And you'll remember we were talking about adenosine...

AUBREY: We were talking about that. That's...

WALKER: Right.

AUBREY: ...Exactly the thing you want to build up to help you sleep.

WALKER: That's right. So adenosine is the sleepiness chemical. So essentially, caffeine comes into your system, and it hits the mute button on the adenosine signal of sleepiness, so it wakes you up. Now, the issue with caffeine is that it has a half-life of about six hours in most people. It has a quarter-life of twelve hours. What I mean by that is if you have a cup of coffee at noon, a quarter of that caffeine is still circulating in your brain at midnight.

AUBREY: Now, some of you may not think this applies to you. And some people are way more sensitive to caffeine than others. But Walker says even if you don't get the caffeine jitters, it can still interrupt the quality of your sleep.

WALKER: Some people will say to me, look. I can have an espresso after dinner. And I fall asleep. And I stay asleep. So no harm, no foul. I'm OK. And the answer is maybe not. We've done these studies where we give people a standard cup of coffee - a dose of, let's say, 180, 200 milligrams of caffeine. Then we put you to bed. And then we measure your sleep. And what we find is that even if you fall asleep and stay asleep, the amount of deep sleep that you get is reduced by about 20 percent.

AUBREY: Ah, so even those people who say I can drink coffee right before I go to bed - they're not exactly right.

WALKER: They're not exactly right because they end up shortchanging their brain in terms of that deep sleep.

AUBREY: And hopefully, if this helps you sleep better, maybe you don't need that 2 p.m. latte. So the bottom line - and this is your take home number two - you want to try to put the brakes on caffeine by late morning.

WALKER: I think people need to be quite mindful of the timing of their caffeine. And the advice usually would be try to stop drinking caffeine about 14 hours before you expect to go to bed.

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AUBREY: Now let's talk about exercise. It's 5:15. I'm trying to get to the spin class at NPR. But everything is going crazy at home. I've got last-minute things to do to work. I'm going to miss it today. So how will missing out on my workout interfere with my sleep tonight?

WALKER: So the relationship between sleep and exercise is quite well understood. And it's bidirectional, in fact.

AUBREY: What do you mean, bidirectional?

WALKER: Well, we started off thinking that exercise had a beneficial impact on sleep. And the answer was yes, it does. But what was even perhaps more powerful statistically was that better sleep at night predicted a greater likelihood that you would actually exercise at all the next day.

AUBREY: So sleep begets exercise. And exercise...

WALKER: Exercise begets sleep.

AUBREY: Now, exercise may help promote sleep in two ways. Physical activity is known to reduce anxiety. So that can help you sleep better. And exercise can also physically tire you out. That can make you sleepy, too. And just to give you a sense of how beneficial exercise can be, Matthew Walker writes in his book about a study of a group of older adults who had sleep issues. They found that after four months of increased physical activity, they were sleeping about an hour more on average per night.

WALKER: If you add that one hour up week after week, month after month, decade after decade, it's like compounding interest on a loan - that it really starts to sort of increase and become quite voluminous in terms of a long-term escalating impact.

AUBREY: OK, so bottom line - I should get to that 5:15 cycling class. Is that what you're telling me?

WALKER: I am.

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AUBREY: So one thing to keep in mind here is that you don't want to exercise too close to bedtime. It can be overstimulating. But the big takeaway here is exercise can help you get better sleep.

WALKER: Always try and get some exercise if you can for better sleep. But just try not to make it in the last two hours before you go to bed. Usually, that can actually be, for some people, a little deleterious.

AUBREY: OK, so where does this leave us? We're going to get more morning light. We're going to cut back on caffeine. We're going to get to that 5:15 cycling class. Now, what about happy hour? I know a lot of us wind down in the evening with a glass of wine or a beer or two. So what's the skinny on alcohol and sleep?

WALKER: Many people see alcohol as a sleep aid. Unfortunately, it's one of the greatest misunderstood substances when it comes to sleep. It is not a sleep aid at all.

AUBREY: It turns out that after an evening of drinking, Walker says our sleep can become fragmented. We tend to wake up more often. And our sleep can be less restful.

WALKER: Alcohol is a very good drug at blocking your dream sleep.

AUBREY: Wow, so you don't even get the REM sleep when you're drinking alcohol?

WALKER: That's right, yeah. Or you get it, but you are shortchanged of a lot of it. This is why a lot of people will tell me, you know, at the weekend, I had a bit too much to drink on Friday. And then I slept in late on Saturday morning. And I was having these bizarre dreams. And I don't know why. And the answer is this - that the alcohol was in your system for the first six or seven hours whilst your liver and kidneys were trying to break it down. And during that time, no REM sleep or very little REM sleep. And when you finally get rid of the alcohol in your system, not only in the last few hours do you get the REM sleep that you were going to have, you get that plus a rebound where the brain tries to get back some of what it's lost. And that explains why you have these really bizarre, really intense dreams after a few too many drinks at night.

AUBREY: And it's not just crazy dreams. Alcohol can get in the way of you consolidating new memories. You know, you write about a study in the book where people were given, I think, three shots of vodka - I guess vodka and orange juice. And they were asked to do some kind of memory task - memorize something. And the researchers found that the ability to memorize the material was greatly reduced when people in the study had something to drink. That was really eye-opening to me.

WALKER: It's frightening, isn't it? It's the sleep after learning that essentially hits the save button on those new memories. And what they found is that alcohol, if you disrupt its sleep the first night after learning, it washed away about 50 percent of the memory. So you were only able to save 50 percent of what you learned rather than 100 percent.

AUBREY: It's really shocking. I mean, it's almost like saying sleep can help you consolidate memory. But drinking alcohol, even having two shots of vodka, can almost counteract it.

WALKER: That's right. You're taking away sleep's benefit - that you are essentially inducing a state of sleep-impaired amnesia.

AUBREY: But there's got to be some amount of alcohol that's OK. I mean, does this happen after only having, say, a glass of wine with dinner? Please tell me no.

WALKER: Sadly, it does.

AUBREY: One glass of wine?

WALKER: We can see it even after - yup.

AUBREY: No.

WALKER: So we've done some of these studies where even just one glass of wine, you can see the - there is a blast radius on sleep. And...

AUBREY: Wow. That is really bad news for a lot of people.

WALKER: You know, I think it's really important for me to say this. All I'm trying to provide you with here is the scientific data so that people listening can make an informed choice. I don't want to sound puritanical. You know, life is to be lived. To an extent, it's all about sort of checks and balances. So just keep this information in mind. But also, you know, just be relaxed about some things, too.

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AUBREY: OK. So now the day is coming to an end. And the last habit you might want to think about changing has to do with what you bring to bed with you. So I've got my laptop. I've got my iPhone. Maybe I've got my iPad with me. I'm going to send one more work email, maybe binge on the last episode of my favorite show. What is wrong with this picture?

WALKER: So what's happening there is, essentially, you're just creating a state of stress. And that state of stress sort of translates biologically or physiologically to an activation of what's called your fight-or-flight branch of the nervous system. And it's that branch of the nervous system that actually needs to switch off for you to be able to fall asleep.

AUBREY: Well, maybe I just want to read my novel on my iPad. I mean, that's not stressful. But I've heard that this blue light can be a problem. Is it?

WALKER: What we've found with studies with one hour of iPad reading versus one hour of just reading in dim light with just a paper book, the iPad actually blocked the release of melatonin by 50 percent - five-zero. So you halved the amount of sleep timing chemical within the brain.

AUBREY: Wow, that's really surprising. Was that surprising to you?

WALKER: Yeah, it was surprising. I think the most surprising result was the timing of it. It wasn't just that the peak of the melatonin was blunted. But when that spike of melatonin arrived was actually three hours later into the night.

AUBREY: In other words, all those devices in your bedroom can delay the onset of your sleep. And what you're really trying to do is wind down. So before you put your head on your pillow tonight, remember, falling asleep is a kind of complicated biological process. And it takes some time.

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AUBREY: So now your day really has come to an end. And Matthew Walker says you really want to aim to give yourself that eight-hour window every night. He says think of it this way. We evolved to sleep.

WALKER: Every species that we've studied to date appears to sleep. What that means is that sleep probably evolved with life itself on this planet. And from that point forward, it has heroically fought its way through every step along the evolutionary pathway. That must mean that if sleep does not serve an absolutely vital set of functions, then it is the biggest mistake that the evolutionary process has ever made.

AUBREY: And if that doesn't make it seem important, what possibly could? So remember, you want to tweak your habits during the day. It really can make getting that sleep you need at night a little easier.

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AUBREY: So you ready to make a change? Let's recap what we've learned. Take away number one, start the day with a splash of sunlight.

WALKER: There is good evidence that morning exposure to daylight helps you sleep better. You get more consistent sleep. And the quality of that sleep tends to be better, as well. So get that good morning daylight.

AUBREY: Takeaway number two, don't overdo the caffeine. It can interrupt your sleep even if you don't notice it.

WALKER: Trying to cut caffeine off somewhere between 12 to 14 hours before you expect to go to bed is a fantastic rule of thumb.

AUBREY: Takeaway number three, exercise can increase the quantity and the quality of your sleep.

WALKER: Exercise during the day as long as it's not too close to sleep at night is sleep promoting. And when you get good sleep, you are far more likely to exercise the following day, as well. It's a golden reciprocal loop.

AUBREY: And takeaway number four, you might want to cut out the nightcap.

WALKER: It's a hard piece of advice. It makes me deeply unpopular. But sound sleep usually comes after a night of no alcohol.

AUBREY: And finally, at bedtime, get those devices out of your bedroom.

WALKER: Try to avoid screens and screen time at least an hour before bed. And if you can, keep those devices out of the room.

AUBREY: Instead, try reading an old-fashioned book. You know, the kind printed on paper.

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AUBREY: That's it for this episode of LIFE KIT. Be sure to check out our next episode. It's about rituals for falling asleep. We'll talk about meditation, melatonin and sex. If you like what you hear, make sure to check out our other LIFE KIT guides at npr.org/lifekit. And while you're there, subscribe to our newsletter, so you don't miss anything. We've got more guides coming every month on all sorts of topics. And here, as always, is a completely random tip, this time from Nicole Cohen of NPR's education team.

NICOLE COHEN, BYLINE: My tip is for cookbooks. I get really overwhelmed by big, beautiful cookbooks. And so I started sitting down and reading through them the way I would a regular book and then just marking all the great-looking recipes. And then after that, I worked my way through all the marked recipes. And it's a really easy way to get a feel for the cooking style without feeling overwhelmed.

AUBREY: If you've got a good tip or you want to suggest a topic, email us at [email protected]. LIFE KIT is produced by Sylvie Douglis, Alissa Escarce, Chloee Weiner. Meghan Keane is our managing producer. Our digital producer is Carol Ritchie. Music by Nick DePrey and Brian Gerhart (ph). Our project manager is Mathilde Piard. Neal Carruth is our general manager of podcasts. And the senior vice president of programming is Anya Grundmann. I'm Allison Aubrey. Thanks for listening.

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