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Thanks to Brilliant for supporting this whole week of SciShow!
感谢Brilliant对本周《科学秀》的大力支持！
Go to Brilliant.org/SciShow to learn more.
登录Brilliant.org/SciShow了解更多。
There's a widespread belief that caffeinated drinks will make you dehydrated
很多人相信咖啡因饮料会让你脱水
because the caffeine itself makes you pee. But is caffeine really a diuretic?
因为咖啡因本身会让你尿尿。但是咖啡因真的利尿么？
Technically, yes, but it's not affecting you as much as you might think.
技术上来讲，确实如此，但它对你的影响并不像你想的那么大。
You might find you need to pee after your morning coffee.
你可能会发现早上喝完咖啡后会想上厕所。
But you may also need to pee after drinking a similar amount of water.
但你喝过同等量水后也会想尿尿啊。
Still is the caffeine making you pee more? It may seem like this would be easy to figure out.
那么咖啡因会让你尿更多么？这似乎很容易算出来。
You just need to know how much liquid goes in and how much comes out, right?
你只需要知道吸入多少液体，排除多少液体就行了，对么？
Actually, it's trickier than that.
但实际比这更棘手。
First of all, people vary a lot in how much liquid they take in, and in how much they pee out.
首先，人们摄入的液体量和排出的尿液量差别很大。
So rather than giving some test subjects coffee and others water,
所以最好的方法不是给受试者咖啡或水，
it's best to measure the same people on different days, plus or minus caffeine.
而是在不同的时间对同一个人进行测量，给他加量或减量咖啡因。
And it may matter when you take a measurement. Kidney output changes with sleep-wake cycles.
在你测量时，这可能很重要。肾脏输出量随睡眠-觉醒周期而变化。
They slow way down overnight, then crank up again during the day.
它们会在夜间减速，然后在清晨再次启动。
So it's probably a good idea to monitor subjects over at least A 24 hour period.
所以至少在24小时内对受试者进行监测可能是个好主意。
Plus, we don't know exactly how much liquid a person needs in a day,
另外，我们不知道一个人一天到底需要多少水，
it depends on who they are and what they're doing.
这取决于他们是谁以及他们在做什么。
Which makes a difference when you're monitoring them for hydration.
当你检测他们的水合作用时，情况就不一样了。
How much water we lose can also change, based on things like how much we exercise or the temperature outside.
我们流失多少水分也会改变，这取决于我们的运动量或室外温度。
You can get around some of this by establishing a baseline fluid intake level for each subject,
你可以通过为每个受试者设定一个基本的液体摄入量来避免这些问题，
and making sure they do basically the same things on their caffeine and non-caffeine days.
并确保他们在咖啡因日或非咖啡因日做一样的事情。
So it's actually quite a challenge to design an experiment that really demonstrates people are gaining or losing water.
所以设计一种真的能够证明人们吸收或流逝多少水分的试验相当具有挑战性的。
That said, researchers over the years have attempted it, just not always successfully.
尽管研究人员多年来一直在尝试，但一直没成功。
The idea that caffeine makes you dehydrated dates back at least several decades, possibly to a study from 1928.
咖啡因会让你脱水的这种想法至少可以追溯到几十年前，可能源于1928年的一项研究。
This study wasn't ideal, since it included just three subjects, and the only measure was urine output.
该研究并不理想，因为它只有三个受试者，并且唯一的测量方法是尿排出量。
I don't know about you, but I'm not going to quit drinking coffee based on ninety-year-old data from three dudes.
不知道大家会怎样，但我是不会因为基于3个人90年前的数据而戒掉咖啡的。
Lucky for all of us, plenty more studies have been done since then,
幸运的是，从那时起，更多的研究已经完成，
looking at the effects of everything from caffeine pills to energy drinks to coffee.
这些研究观测了从咖啡因药片到能量饮料再到咖啡的各种效果。
When you look at all the data together, some trends emerge.
当你把所有的数据放在一起看，就会发现一些趋势。
A moderate amount of caffeine, in the neighborhood of 300 to 500 milligrams,
在多数研究中，大约300到500毫克的适量咖啡
does not seem to lead to water loss in most studies.
似乎不会导致水分的流逝。
That's the equivalent of 2 to 3 cups of barista-brewed coffee, or 6 cups of tea, or more than 2.5 liters of cola.
这个量相当于2到3杯的滴漏式咖啡，或6杯茶，或超过2.5公升的可乐。
When you go above those amounts, caffeine can have a minor diuretic effect.
当你超过以上这些量时，咖啡因会有轻微的利尿作用。
But, as even those researchers back in 1928 recognized, if you have caffeine every day,
但即使是1928年的那些研究人员也认识到，如果你每天摄入咖啡因，
you quickly become resistant to its dehydrating effects.
你很快就会对它的脱水效果产生抵抗力。
In one 1997 study, the diuretic effect of even a relatively high dose of caffeine also disappeared when the subjects were exercising.
在1997年的一项研究中，即使是相对高剂量的咖啡因的利尿作用也会在受试者运动时消失。
This myth has a surprising amount of staying power.
这个虚构的想法还真是经久不衰。
It's everywhere, and even some medical professionals continue to spread outdated guidelines. But take comfort.
它无处不在，甚至一些医学专业人士继续传播过时的指南。但没关系。
The research is clear: drinking a few servings of coffee, tea, or caffeinated soda will not make you dehydrated.
这项研究很明确：喝一点咖啡、茶或咖啡苏打不会让你脱水。
There may be other reasons to stay away from sugary, caffeinated drinks but hydration isn't one of them.
也许还有其他原因让你远离含糖、含咖啡因的饮料，但水合作用不是其中之一。
If you've got a caffeine buzz going from this high-energy episode, and you're wondering what to do next,
如果你在本期视频中对咖啡因产生兴趣，并且你在想下一步该怎么办，
you could keep your learning streak going with a course on Brilliant.org.
你可以在Brilliant.org继续学习。
Brilliant has courses that can help you hone your math and science skills.
Brilliant中的课程可以帮助你磨练你的数学和科学技能。
They're hands-on, interactive, and illustrated to help you pick up even their advanced topics.
它们是互动式的，并且有插图帮助你理解进阶级话题。
With Brilliant, you'll be learning multivariable calculus in no time.
有了Brilliant，你将很快便能学习多变量微积分。
And the first 200 people to sign up at Brilliant.org/SciShow will get 20% off an annual Premium subscription to Brilliant.org.
前200名注册Brilliant.org/SciShow的观众将获得年度订阅8折优惠。
And supporting them supports us too, so thanks for checking them out.
支持他们的同时也会在支持我们，所以感谢关注。
