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我们每天该喝多少水才够?

更新时间:2019/6/17 18:13:56 来源:纽约时报中文网 作者:佚名

How much water should you drink a day?
我们每天该喝多少水才够?

In the early 19th Century, people had to be close to death before deigning to drink water. Only those “reduced to the last stage of poverty satisfy their thirst with water”, according to Vincent Priessnitz, the founder of hydropathy, otherwise known as “the water cure”.

19世纪初期,人们只有在垂死的时候才会“屈尊”喝水。水疗法,顾名思义就是“用水治病”,其创始人普雷斯尼茨(Vincent Priessnitz)表示:“当时,只有穷得叮当响的人才会喝白开水解渴。”

Many people, he added, had never drunk more than half a pint of plain water in one sitting.

他补充说,很少有人一次喝下超过半品脱的白开水。

How times have changed. Adults in the UK today are consuming more water now than in recent years, while in the US, sales of bottled water recently surpassed sales of soda. We’ve been bombarded with messages telling us that drinking litres of water every day is the secret to good health, more energy and great skin, and that it will make us lose weight and avoid cancer.

但是时光飞逝,今时已不同往日。如今,英国成年人的饮水量在近几年达到顶峰。最近在美国,瓶装水的销量超过了碳酸饮料。生活中,我们被各种各样的信息狂轰滥炸:每天喝几升水是保持健康活力和拥有美丽肌肤的秘诀,能减肥,使我们远离癌症。

Commuters are encouraged to take bottles of water onto the London Underground, pupils are advised to bring water into their lessons and few office meetings can commence without a giant jug of water sitting in the middle of the desk.

英国政府鼓励上班族携带水瓶乘坐伦敦地铁,小学生们也被鼓励带水到课堂饮用,而且几乎所有公司开会时都会在桌子中间放一大壶水。

Fuelling this appetite for water is the “8x8 rule”: the unofficial advice recommending we drink eight 240ml glasses of water per day, totalling just under two litres, on top of any other drinks.

有一条非官方建议叫“8乘8法则”,建议我们除了任何其他的饮料之外,每天还要喝8杯240毫升的水,总量接近两升。

That “rule”, however, isn’t backed by scientific findings – nor do UK or EU official guidelines say we should be drinking this much.

然而,这一“法则”并没有任何科学支持。英国或欧盟的官方指南并没有建议我们喝这么多水。

Where did it come from? Most likely, it seems, from misinterpretations of two pieces of guidance – both from decades ago.

那么,这种说法到底源自哪里呢?最有可能的原因似乎是人们误读了两项几十年前出台的指导方针。

In 1945 the US Food and Nutrition Board of the National Research Council advised adults to consume one millilitre of liquid for every recommended calorie of food, which equates to two litres for women on a 2,000-calorie diet and two-and-a-half for men eating 2,500 calories. Not just water, that included most types of drinks – as well as fruits and vegetables, which can contain up to 98% water.

1945年,美国国家研究委员会(National Research Council)的食品与营养委员会(Food and Nutrition Board)建议,成年人每食用一卡路里食物,就要摄入一毫升液体。女性如果摄入2000卡路里的食物就要喝两升液体,而摄入2500卡路里的男性则需要饮用2.5升液体。

In 1974, meanwhile, the book Nutrition for Good Health, co-authored by nutritionists Margaret McWilliams and Frederick Stare, recommended that the average adult consumes between six to eight glasses of water a day. But, the authors wrote, this can include fruit and veg, caffeinated and soft drinks, even beer.

1974年, 营养学家麦克威廉姆斯(Margaret McWilliams)和斯塔勒(Frederick Stare)合著的《健康好营养》(Nutrition for Good Health)一书建议,成年人平均每天饮用6至8杯水,但作者认为这应包括水果、蔬菜、咖啡因、饮料甚至啤酒。

In thirst we trust

相信口渴的感觉

Water is, of course, important. Making up around two-thirds of our body weight, water carries nutrients and waste products around our bodies, regulates our temperature, acts as a lubricant and shock absorber in our joints and plays a role in most chemical reactions happening inside us.

水很重要,约占人体体重的三分之二,将营养物质和废物运送到身体各处,能调节体温,在关节中充当润滑剂和减震器,并在人体内大多数化学反应中发挥重要作用。

We’re constantly losing water through sweat, urination and breathing. Ensuring we have enough water is a fine balance, and crucial to avoiding dehydration. The symptoms of dehydration can become detectable when we lose between 1-2% of our body’s water and we continue to deteriorate until we top our fluids back up. In rare cases, such dehydration can be fatal.

我们在流汗、排尿和呼吸时会流失水分。保证身体水分充足,能够避免脱水。当身体流失了1-2%的水分时,就会出现脱水症状,如果不补充水,情况就会持续恶化。在少数情况下,脱水可能致命。

Years of unsubstantiated claims around the 8x8 rule have led us to believe that feeling thirsty means we’re already dangerously dehydrated. But experts largely agree that we don’t need any more fluid than the amount our bodies signal for, when it signals for it.

未经证实的“8乘8法则”让我们相信,感到口渴意味着我们已经处于危险的脱水状态。但专家们则认为,当身体发出信号时,我们不需要摄入过多的水,适当即可。

“The control of hydration is some of most sophisticated things we’ve developed in evolution, ever since ancestors crawled out of sea onto land. We have a huge number of sophisticated techniques we use to maintain adequate hydration,” says Irwin Rosenburg, senior scientist at the Neuroscience and Ageing Laboratory at Tufts University in Massachusetts.

“水合作用是人类从海洋进化到陆地后演变出的一项复杂功能。人体有很多复杂的方法可以保持水分充足。”马萨诸塞州塔夫茨大学(Tufts University)神经科学与衰老实验室(Neuroscience and Aging Laboratory)资深科学家罗森伯格(Irwin Rosenburg)表示。

In a healthy body, the brain detects when the body is becoming dehydrated and initiates thirst to stimulate drinking. It also releases a hormone which signals to the kidneys to conserve water by concentrating the urine.

健康状况正常时,大脑会检测身体什么时候开始脱水,并通过口渴的感觉来提醒人们喝水,同时还会释放一种激素,告诉肾脏储蓄尿液来保持水分。

“If you listen to your body, it’ll tell you when it's thirsty,” says Courtney Kipps, consultant sports physician and principal clinical teaching fellow of Sports Medicine, Exercise and Health and UCL, and medical director of Blenheim and London Triathlons.

“如果你仔细聆听,身体会告诉你它什么时候渴了。”运动医学顾问医师基普斯(Courtney Kipps)说。他是伦敦大学学院运动医学、运动与健康临床教学主任、布伦海姆和伦敦铁人三项运动(Blenheim and London Triathlons)医学主任。

“The myth that it’s too late when you’re thirsty is based on the supposition that thirst is an imperfect marker of a fluid deficit, but why should everything else in the body be perfect and thirst be imperfect? It’s worked very well for thousands of years of human evolution.”

“当你感到口渴时,一切都太迟了,此论断基于这样一种假设,即表明体液不足,口渴并非一个良好指标。为什么人体中的其他一切指标都是准确的,而只有口渴有问题呢?在人类几千年的进化过程中,口渴机制一直运行良好。”

While water is the healthiest option since it has no calories, other drinks also hydrate us, including tea and coffee. Although caffeine has a mild diuretic effect, research indicates that tea and coffee still contribute to hydration – and so do alcoholic drinks.

水不含卡路里,是最健康的选择,但其他饮料也能为我们的身体补充水分,包括茶和咖啡。虽然咖啡因有轻微的利尿作用,但研究表明,茶和咖啡仍然有助于水合作用,酒精饮料也是如此。

Drinking to good health

喝出健康

There’s little evidence suggesting that drinking more water than our body signals for offers any benefits beyond the point of avoiding dehydration.

除了避免脱水,几乎没有证据表明超过身体所需喝水还有其他好处。

Still, research suggests there are some important benefits to avoiding even the early stages of mild dehydration. A number of studies have found, for example, that drinking enough to avoid mild dehydration helps support brain function and our ability to do simple tasks, such as problem-solving.

不过,研究表明,在轻度脱水的早期阶段就开始喝水确实有作用。例如,许多研究发现,通过喝水避免轻度脱水有助于增强大脑功能,提高完成简单任务(比如解决问题)的能力。

Some studies suggest fluid consumption can help manage weight. Brenda Davy, a professor of human nutrition, food and exercise at Virginia Polytechnic Institute and State University, has carried out a few studies looking at fluid consumption and weight.

一些研究表明,摄入液体有助于控制体重。弗吉尼亚理工学院(Virginia Polytechnic Institute)和弗吉尼亚州立大学(State University)的人类营养、食品和运动教授戴维(Brenda Davy)进行了有关液体消耗和体重的研究。

In one study, she randomly assigned subjects to one of two groups. Both groups were asked to follow a healthy diet for three months, but only one was told to drink a 500ml glass of water half an hour before eating each meal. The group who drank the water lost more weight than the other group.

在一项研究中,她将受试者随机分为两组。两组都被要求遵循健康饮食三个月,但只有一组需要在饭前半小时喝500毫升的水。结果显示,喝水的那组比另一组减重更多。

Both groups were also told to aim for 10,000 steps a day, and those who drank the glasses of water better adhered to this. Davy guesses this is because mild dehydration of around 1-2% is quite common, and many people may not realise when this happens – and even this mild level can affect our mood and energy levels.

两组受试者每天都要走一万步,但喝水的一组坚持得更久。戴维猜测,这是因为1-2%左右的轻度脱水很常见,很多人可能甚至都没有意识到,但即使是这种轻度脱水也会影响我们的情绪和能量水平。

But Barbara Rolls, a professor of intensive care medicine at University College London, says that any weight loss associated with drinking water is more likely to come from water being used as a substitute for sugary drinks.

但是伦敦大学学院重症监护医学教授罗尔斯(Barbara Rolls)说,喝水能减肥可能是因为水替代了含糖饮料。

“The notion that filling up on water before a meal will melt the pounds away is not well established, and water consumed on its own empties out of the stomach really quickly. But if you consume more water through the food you eat, such as soup, this can help fill you up as the water is bound to the food and stays in the stomach for longer,” she says.

“饭前喝水能减肥的观点并不对,因为你喝下去的水很快就会从胃里排出。但是,如果你通过食物摄取更多的水,比如说汤,就会产生饱腹感,因为水与食物结合在一起,在胃里停留的时间更长。”她说。

Another alleged health benefit of drinking more water is improved skin complexion and better moisturised skin. But there is a lack of evidence to suggest a credible scientific mechanism behind this.

据说多喝水对健康的另一个好处是能改善肤色和保湿肌肤,但这一说法缺乏科学证据。

Too much of a good thing?

物极必反

Those of us aiming for eight glasses of water per day aren’t doing ourselves any harm. But the belief we need to drink more water than our bodies signal for can sometimes become dangerous.

每天喝8杯水并不会危害健康。但是,有时候“觉得自己一定要喝超过身体所需的水”这种想法会带来危害。

Too much fluid consumption can become serious when it causes a dilution of sodium in blood. This creates a swelling of the brain and lungs, as fluid shifts to try to balance out blood sodium levels.

摄入过多液体会稀释血液中的钠,可能会导致脑部和肺的肿胀,这时情况就危险了。因为体液为了平衡血液中的钠含量会自行转移。

Over the last decade or so, Kipps has been aware of at least 15 cases of athletes who’ve died from over-hydration during sporting events. She suspects these cases are partly because we’ve become distrustful of our own thirst mechanism and that we think we need to drink more than our bodies are calling for to avoid dehydration.

在过去10年左右的时间里,基普斯发现有至少15名运动员在体育赛事期间死于过度饮水。她认为部分原因是我们不信任口渴反应,认为需要喝比身体所需更多的水,以避免脱水。

“Nurses and doctors in hospitals will see severely dehydrated patients who have serious medical conditions or who haven’t been able to drink for days, but these cases are very different from the dehydration that people worry about during marathons,” she says.

她说:“医院的护士和医生会碰到情况十分严重的重度脱水病人,或者已经好几天无法喝水了,但这些情况和人们在马拉松比赛中担心的脱水非常不同。”

Johanna Pakenham ran the 2018 London Marathon, the hottest on record. But she can’t remember most of it because she drank so much water during the race that she developed over-hydration, known as hyponatremia. She was rushed to hospital later that day.

帕克纳姆(Johanna Pakenham)参加了2018年的伦敦马拉松,这是有记录以来天气最热的一次,但她已不记得当时的情况,因为在比赛中喝了太多的水,帕克纳姆出现了水合过度,又被称为“低钠血症”。当天晚些时候,她被紧急送往医院。

“My friend and partner thought I was dehydrated and they gave me a big glass of water. I had a massive fit and my heart stopped. I was airlifted to hospital and unconscious from the Sunday evening until the following Tuesday,” she says.

“我的朋友和伴侣以为我脱水了,就给我喝了一大杯水。随后,我开始全身痉挛,心脏停止跳动。后来,我被救护直升机送到医院,从周日晚上一直昏迷到下周二,”她说。

Pakenham, who plans to run the marathon again this year, says the only health advice offered by friends and marathon posters was to drink lots of water.

帕克纳姆今年还打算参加马拉松比赛,她说朋友们和马拉松海报提供的唯一健康建议就是多喝水。

“All it would’ve taken for me to be okay was having a few electrolyte tablets, which increase the sodium levels in your blood. I’ve ran a few marathons before and I didn’t know that,” she says.

“我只要吃几片电解质片就好了,能提高血液中的钠含量。我以前跑过几次马拉松,但我当时不知道。”她说。

“I really want people to know that something so simple can be so deadly.”

“我真的很想告诉人们,如此简单的事情也可能致命。”

How much?

喝多少为好?

The idea that we must be constantly hydrated means many people carry water with them wherever they go, and drink more than their bodies require.

“我们必须经常补水”这种想法意味着很多人无论走到哪里都要随身携带水,并且比身体所需喝的多。

“The maximum a person in the hottest possible heat in the middle of the desert might sweat is two litres in an hour, but that’s really hard,” says Hugh Montgomery, director of research at the Institute for Sport, Exercise and Health in London.

伦敦运动、锻炼与健康研究所(Institute for Sport, Exercise and Health)的研究主管蒙哥马利(Hugh Montgomery)表示:“一个人在沙漠高温环境下每小时排汗量为2升,但这种情况真的很难碰到。”

“The idea of carrying around 500ml of water for a 20-minute journey on the London Underground – you’re never going to get hot enough to sweat at that rate, even if you’re dripping with sweat.”

“你带500毫升的水坐20分钟伦敦地铁,怎么样也不会像在沙漠里那样出汗。”

For those who feel more comfortable going off official guidelines rather than thirst, the UK’s NHS advises drinking between six to eight glasses of fluid a day, including lower fat milk and sugar-free drinks, including tea and coffee.

英国国民保健系统(NHS)建议,对于那些不按官方指引喝水也不会觉得口渴的人,每天喝6到8杯液体即可,包括低脂牛奶、无糖饮料、茶和咖啡。

It’s also important to remember that our thirst mechanisms lose sensitivity once we’re over 60.

还要记住一点,人到了60岁,口渴机制就会失去敏感度。

“As we age, our natural thirst mechanism becomes less sensitive and we become more prone to dehydration than younger people. As we age, we may need to be more attentive to our fluid consumption habits to stay hydrated,” says Davy.

“随着年龄增长,我们天生的口渴机制会变得迟钝,比年轻人更容易脱水。所以,人老了后需要更注意自己的饮水习惯,以保持水分,”戴维说。

Most experts agree that our fluid requirements vary depending on a person’s age, body size, gender, environment and level of physical activity.

大多数专家都认为,我们对液体的需求取决于年龄、体型、性别、环境和运动水平。

“One of fallacies of the 8x8 rule is its stark over-simplification of how we as organisms respond to the environment we’re in,” says Rosenburg. “We ought to think of fluid requirement in the same way as energy requirement, where we talk about the temperature we’re in and level of physical activity were engaged in.”

罗森伯格说:“8乘8法则的一个错误之处在于,它把人类作为有机体对所处环境的反应完全简单化了。我们应该用能量需求的方式来计算应摄入的液体量,包括我们所处的环境温度和体能活动的水平。”

Most experts tend to agree we don’t need to be concerned about drinking an arbitrary amount of water per day: our bodies signal to us when we’re thirsty, much like they do when we’re hungry or tired. The only health benefit of drinking more than you need, it seems, will be the extra calories you expend by running to the loo more often.

大多数专家认为,我们其实不需要担心每天喝多少水。当我们口渴时,身体会发出信号,就像肚子饿了或身体累了一样。喝过量水对健康的唯一好处可就是跑厕所消耗的额外热量。

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