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讲堂｜一天要不要喝8杯水？
(Credit: Dr. Joseph Mercola)
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你听过每人每天得喝八杯水的理论吗？詹妮弗·冈特医生说那其实是个谣言。很多人不了解自己身体背后的生物学知识，接收的都是错误的信息。在这个演讲中，她讲解了精密的肾脏如何让人体保持在一个平衡点，以及如何判断身体是否脱水。那么我们一天到底应该喝多少水呢？让我们来看看詹妮弗·冈特医生的播客Body Stuff上面的科普吧。
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Why You Don’t Need 8 Glasses of Water a Day
为何不需要一天喝8杯水
Many people don’t understand the biology behind their bodies. There’s a lot of misinformation out there. But the truth is that when you understand how your systems function, you’re able to make better decisions. You’re not as prone to fall for hype or pseudoscience. You’ll feel empowered to understand what’s really going on.很多人不了解自己身体背后的生物学知识，错误信息满天飞。但一旦明白身体是如何运作的，你就能做出更好的决定。不会轻易掉入虚假宣传和伪科学的陷阱，你就能更好地了解你的身体。
One myth that really bugs me is the idea that you need eight glasses of water a day. Honestly, it’s pretty shocking how ingrained it is. You hear it on TV, you see it in articles. But like I said, it’s nonsense. For the most part, your body will tell you when you need to drink water, because you’ve got these wonderful, amazing, undervalued things — kidneys.有一个谣言让我真的不爽，就是人每天需要喝8杯水。实话说，这谣言真的流传甚广。电视里有人讲，文章里有人写。但就像我刚刚说的，这完全是瞎扯。绝大部分情况下，你的身体会提醒你该喝水了，因为人体拥有奇妙的、神奇的、被大大低估的器官——肾。
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Kidneys are the bean-shaped organs located to either side of your spine, right below your ribs. They’re often thought of as a filter or a waste-removal system, but that doesn’t do the kidneys justice. Your body is an environment where everything, fluid and chemicals, needs to be in a delicate balance. The kidneys do a lot of the heavy lifting when it comes to this balance. Every day, blood in your body passes through the kidneys. What you eat, drink, the temperature around you, how much you exercise — all of this affects what’s going on with your body. Your kidneys, along with your nervous system and various hormones, are constantly watching many gauges and making adjustments about fluid, salt and levels of other substances in real time.肾脏是位于人体脊柱两侧的豆状器官，在肋骨下面一点点。它们经常被认为是过滤器或垃圾清除系统，但这还不能完全描述肾脏的作用。人体是一个需要保持精妙平衡的环境，无论是体液还是化学物质。肾脏在维持这种平衡的过程中发挥了重要作用。每天身体里的血液都要经过肾脏。人们每天吃的、喝的、所处的环境温度及运动量，所有这些都会影响身体。人体的肾脏，连同神经系统和各种荷尔蒙，在不间断地观察多项指标，实时调整着体液、盐分和其他物质的水平。 They do this with about one million tiny structures called nephrons. These nephrons are kind of like workers on a conveyor belt, actively adding things and taking things away, things like sodium, glucose or sugar, calcium, amino acids and water, to make sure the body maintains homeostasis, or balance. If levels of anything get too high or too low, then that can be harmful. And it is the job of the kidneys to keep the levels of many of these substances in the just-right zone. Substances that aren’t needed leave the kidney and head to the bladder, where you excrete them in the form of urine.肾脏通过100万个微小的结构来完成上述工作，这种微小结构叫肾元。肾元有点像流水线旁的工人，不停地往里加点什么或拿走点什么，比如钠、葡萄糖或糖，钙、氨基酸和水，保证身体处于平衡的状态。任何物质过多或过少都可能有害。肾脏的作用就是将多种物质的含量保持在恰当的区间内。不需要的物质会离开肾脏，流向膀胱，在那里以尿液的形式排出体外。
So where do eight glasses of water a day fit in? They don’t. Noticed that I did not say that the kidney function is improved with excess water. Imagine that you’re sweating a lot, so you’re losing water from your blood. The kidneys know your blood volume is dropping ever so slightly and that your blood is getting ever so slightly saltier. They compensate by absorbing more water back into the blood, making the urine more concentrated. If the kidneys sense enough fluid can’t be reabsorbed from the urine, you’re signaled to drink, meaning you get thirsty. If you don’t have fluid available, the thirst message gets stronger and stronger. A person facing real dehydration won’t be unsure if they need water. They’ll do whatever they need to get it. It’s one of our most basic instincts that’s evolved over a very long time, in environments where clean water wasn’t nearly as readily available as it is today.这中间哪一步需要一天8杯水呢？都不需要。请注意我刚刚并没有说肾功能会因为额外的水份而得到改善。想象一下，你出了很多汗，因此血液里的水份减少了。肾脏会注意到你的血量下降了一点点，因此导致血液里的含盐量上升了一点点。它们会通过多吸收一些水回血液来进行补偿，这样会导致你的尿更浓一些。如果肾脏发现尿液里的水也不够它们重新吸收的，它们就会提醒你喝水，这时你就会觉得渴。如果你没有喝水的话，这种口渴的感觉就会越来越强烈。一个真的面临脱水状况的人，是不可能拿不准自己是不是需要水的。他们会想尽一切办法去搞到水。这是我们最基础的本能之一，是经历了漫长的进化过程得来的， 当时的环境并不像今天这样——清洁的水唾手可得。
So thanks to your kidneys, your body is really good at maintaining hydration. But if you stop counting eight glasses of water a day, how much should you be drinking? The answer is simple: there is no should. When you feel thirsty, drink some water. You can trust your body. Unless you have kidney stones or are elderly — sometimes, our messaging systems get a little worn with age — or your doctor has told you otherwise, constantly monitoring how much water you drink is not really necessary.因此，多亏肾脏，人体才会非常善于保持水份充足的状态。但是，如果一天不需要喝8杯水，那到底应该喝多少呢？答案很简单，没有定量。你什么时候觉得渴了，就去喝点水。你可以相信自己的身体。除非你有肾结石，或者年纪大了，有时候我们的信息传递系统会随着年龄增长变迟钝，又或者你的医生有吩咐，否则，持续监测自己喝了多少水，真的完全没必要。
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Here’s a point that’s often missed: every single thing you consume contains water. Your morning coffee has water, so does your breakfast. And that snack — an apple, an orange, a glass of juice, a granola bar — just like you, they’re made of water too. So as long as you’re listening to your body’s internal sense of thirst, there’s really no need to be counting those eight glasses.还有一点经常被忽视：你吃的每一样食物都含有水。你早上的咖啡里有水，你的早餐里也含水。你的零食——无论是苹果、橙子、果汁、燕麦卷——就像你自己一样，它们都含有水分。所以，只需要听从身体里发出的口渴的信号， 每天数着喝8杯水真的没必要。