Most Americans have heard that they should drink eight glasses of water a day to stay hydrated, but there is surprisingly little data to support this advice.

大多数美国人都曾听说日饮八杯水对补水的重要性。出人意料是，这个建议基本没有任何数据支持。

But now, a new “beverage¹ hydration index” provides evidence-based suggestions for how to most efficiently² hydrate. The index was developed from a British study published in December that tracked how long 13 common beverages³ remain in the body after being consumed.

但现在，新出台的“饮品补水指数”为高效补水的方式提供了有证据的建议。这项指数基于2015年12月英国发布的一项研究，追踪记录了13种常见饮品在被摄取后停留人体的时间。

“In the last 25 years, we’ve done many studies on rehydration after exercise,” said Ronald J. Maughan, a hydration expert from Loughborough University, and lead author of the study. “We thought it was time to look at hydration in typical consumers who aren’t exercising.”

“在过去的25年中，我们针对运动后人们的补水状况进行了许多研究，”罗纳德•J•莫恩说道，他是拉夫堡大学的补水研究专家，同时也是这项研究的主要作者。“我们认为是时候研究不运动人群的补水状况了。”

The hydration index is modeled after the well-known glycemic index, which measures how the body responds to the carbohydrate⁴ content of different foods. (The glycemic index is used to help individuals keep their glucose-insulin response under control.) The guiding principle behind the new hydration index is that some fluids last longer in your body than others, providing more hydration. After all, if you drink a cup of water and then immediately excrete half that amount in your urine, you haven’t added eight ounces to your water supply, but only four.

补水指数的设定参照了众所周知的血糖指数，血糖指数测量的是身体对不同食物中碳水化合物的反应。（血糖指数用于帮助人们血糖-胰岛素维持稳态。）新的补水指数的指导原则是：某些液体在体内留存更久，因此具备更好的补水能力。毕竟，你若是饮下一杯八盎司的水，而后立即小解排出一半，那么你真正吸收的水量只有四盎司。

The British study determined⁶ the hydration index of 13 common beverages by having the participants, 72 males in their mid-20s, drink a liter of water as the standard beverage. The amount of water still remaining in subjects’ bodies two hours later — that is, not voided in urine — was assigned a score of 1.0. All other beverages were evaluated in a similar manner, and then scored in comparison to water. A score higher than 1.0 indicated that more of the beverage remained in the body as compared to water, while a score lower than 1.0 indicated a higher excretion rate than water.

英国的这项研究检测了13种常见饮品在72位男性身体中的补水指数，这些受测者的年龄均在25岁左右，他们在测试初饮用了一公升的水作为参照标准。两小时后受测者体内水分含量——即未经由尿液流失的液体量——被记录为1.0。然后以相似的方式测试其他饮料的补水指数，再将其与水的指数作比较。高于1.0的饮料的体内水分留存率高于水，低于1.0的饮料排出率高于水。

The results showed that four beverages — oral rehydration solution, like Pedialyte; fat-free milk; whole milk and orange juice — had a significantly higher hydration index than water. The first three had hydration index scores around 1.5, with orange juice doing slightly better than water at 1.1. Oral rehydration solutions are specifically formulated⁷ to combat serious dehydration⁸ such as that resulting from chronic⁹ diarrhea.

研究显示有四种饮料的补水指数远高于水，它们分别是以电解质液体为代表的口服补水溶液；脱脂牛奶；全脂牛奶和橙汁。前三种饮料的补水指数高达1.5左右，橙汁的补水指数为1.1，比水略高。口服补水溶液是为应对严重脱水（如慢性腹泻所引发的脱水）而配制的。

“It’s a very clever, even brilliant study,” said Lawrence Armstrong, a hydration expert at the University of Connecticut and immediate⁵ past president of the American College of Sports Medicine. “It assumes that water is the optimal¹⁰ rehydration fluid, which is biologically correct, and then compares other fluids to water.”

“这是一项相当聪明，也很精彩的研究，”康涅狄格大学的补水专家、即将卸任的美国运动医学会主席劳伦斯•阿姆斯特朗表示。“它假定水为最理想的补水液体——从生物学角度而言的确如此——然后再将其他液体与水作比较。”

Why is milk so efficient at rehydration? “Normally when you drink, it signals the kidneys to get rid of the extra water by producing more urine,” Dr. Maughan said. “However, when beverages contain nutrients¹¹ and electrolytes like sodium¹² and potassium, as milk does, the stomach empties more slowly with a less dramatic effect on the kidneys.”

牛奶高效补水的原理是什么？“通常当你摄取水分时，肾脏会收到通过产生尿液来排出多余水分的指令，”莫恩博士说道，“但是若你饮用的液体含有营养成分和诸如钠和钾这样的电解质，比如饮用牛奶，那么胃的排空速率就会变慢，肾脏因此收到的指令变弱。”

Perhaps surprisingly, drinks containing moderate amounts of caffeine and alcohol or high levels of sugar had hydration indexes no different from water. In other words, coffee and beer are not dehydrating, despite common beliefs to the contrary, and regular soda can hydrate you just as well as water.

让人大感意外的是，含适量咖啡因、酒精或含糖高的饮料与普通水的补水指数相当。换句话来说，饮用咖啡和啤酒不易脱水，虽然这与人们的常识相左。同时，苏打水能和普通水一样带来同样的补水效果。

“It’s true that caffeine is a diuretic, but not at the concentration found in most coffee drinks,” Dr. Maughan said. “When we are thirsty, drinking normal tea, coffee or cola helps to rehydrate us. The exceptions are very strong coffee drinks or strong alcoholic¹³ drinks like distilled¹⁴ spirits.”

“咖啡因确实具备利尿效果，但大部分咖啡饮料都达不到那么高的浓度，”莫恩博士说道。“当我们口渴的时候，饮用普通的茶、咖啡和可乐一样能够补水，除非饮用的是高浓度咖啡或是蒸馏酒那样烈性酒。”

The hydration index could prove useful when making decisions about what beverages to consume and when. For example, if you’re going on a long drive and won’t have access to fluids (or to bathrooms), you’d be smarter to drink milk with its high hydration index rather than water or iced coffee. But don’t forget that milk has many more calories than water, so don’t overdo¹⁵ it, either.

补水指数对于决定何时饮用何种饮料或许大有用处。例如当你驾驶长途车，且有很长时间都不方便饮水（或是上厕所）时，饮用牛奶（补水指数高于水和冰咖啡）才是个明智之选。但别忘了牛奶比水含有更多的卡路里，喝奶虽好，可不要贪杯噢。

While severe dehydration is rare except in heavy exercise, extreme environments and disease, studies have shown that heat and dehydration can contribute to increased mortality rates during hot weather. “Mortality increases sharply during heat waves, mostly because people don’t drink enough to compensate¹⁶ for their increased fluid losses,” Dr. Maughan said.

虽说除了剧烈运动、极端环境或是患病时，人们一般不会严重缺水，但研究显示，炎热天气下的高温脱水会提高死亡率。“在热浪袭来时，死亡率往往会急剧攀升，这主要是因为人们没有及时补充他们流失掉的水分。”莫恩博士说道。

Dr. Armstrong noted¹⁷ that in hot weather, it’s important to monitor your hydration status throughout the day. He suggested paying attention to your thirst, and drinking when necessary. Also, if your urine color is a dark yellow, it’s time for a refreshing¹⁸ drink.

莫恩博士指出，在高温天气下，人们非常有必要全天注意体内的含水状况。他建议人们多注意自身的口渴状况，必要时补充水分。此外，若是你的尿液已经呈现深黄色，是时候补充水分了。