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.
大多數美國人都曾聽說日飲八杯水對補水的重要性。出人意料是，這個建議基本沒有任何數據支持。

But now, a new “beverage hydration index” provides evidence-based suggestions for how to most efficiently hydrate. The index was developed from a British study published in December that tracked how long 13 common beverages remain in the body after being consumed.
但現在，新出臺的“飲品補水指數”為高效補水的方式提供了有證據的建議。這項指數基于2015年12月英國發布的一項研究，追蹤記錄了13種常見飲品在被攝取后停留人體的時間。

“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.”
“在過去的25年中，我們針對運動后人們的補水狀況進行了許多研究，”羅納德?J?莫恩說道，他是拉夫堡大學的補水研究專家，同時也是這項研究的主要作者。“我們認為是時候研究不運動人群的補水狀況了。”

The hydration index is modeled after the well-known glycemic index, which measures how the body responds to the carbohydrate 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.
補水指數的設定參照了眾所周知的血糖指數，血糖指數測量的是身體對不同食物中碳水化合物的反應。（血糖指數用于幫助人們血糖-胰島素維持穩態。）新的補水指數的指導原則是：某些液體在體內留存更久，因此具備更好的補水能力。畢竟，你若是飲下一杯八盎司的水，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 determined 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.
英國的這項研究檢測了13種常見飲品在72位男性身體中的補水指數，這些受測者的年齡均在25歲左右，他們在測試初飲用了一公升的水作為參照標準。兩小時后受測者體內水分含量——即未經由尿液流失的液體量——被記錄為1.0。然后以相似的方式測試其他飲料的補水指數，再將其與水的指數作比較。高于1.0的飲料的體內水分留存率高于水，低于1.0的飲料排出率高于水。

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 formulated to combat serious dehydration such as that resulting from chronic diarrhea.
研究顯示有四種飲料的補水指數遠高于水，它們分別是以電解質液體為代表的口服補水溶液；脫脂牛奶；全脂牛奶和橙汁。前三種飲料的補水指數高達1.5左右，橙汁的補水指數為1.1，比水略高。口服補水溶液是為應對嚴重脫水（如慢性腹瀉所引發的脫水）而配制的。

“It’s a very clever, even brilliant study,” said Lawrence Armstrong, a hydration expert at the University of Connecticut and immediate past president of the American College of Sports Medicine. “It assumes that water is the optimal rehydration fluid, which is biologically correct, and then compares other fluids to water.”
“這是一項相當聰明，也很精彩的研究，”康涅狄格大學的補水專家、即將卸任的美國運動醫學會主席勞倫斯?阿姆斯特朗表示。“它假定水為最理想的補水液體——從生物學角度而言的確如此——然后再將其他液體與水作比較。”

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 nutrients and electrolytes like sodium and potassium, as milk does, the stomach empties more slowly with a less dramatic effect on the kidneys.”
牛奶高效補水的原理是什么？“通常當你攝取水分時，腎臟會收到通過產生尿液來排出多余水分的指令，”莫恩博士說道，“但是若你飲用的液體含有營養成分和諸如鈉和鉀這樣的電解質，比如飲用牛奶，那么胃的排空速率就會變慢，腎臟因此收到的指令變弱。”

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.
讓人大感意外的是，含適量咖啡因、酒精或含糖高的飲料與普通水的補水指數相當。換句話來說，飲用咖啡和啤酒不易脫水，雖然這與人們的常識相左。同時，蘇打水能和普通水一樣帶來同樣的補水效果。

“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 alcoholic drinks like distilled spirits.”
“咖啡因確實具備利尿效果，但大部分咖啡飲料都達不到那么高的濃度，”莫恩博士說道。“當我們口渴的時候，飲用普通的茶、咖啡和可樂一樣能夠補水，除非飲用的是高濃度咖啡或是蒸餾酒那樣烈性酒。”

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 overdo it, either.
補水指數對于決定何時飲用何種飲料或許大有用處。例如當你駕駛長途車，且有很長時間都不方便飲水（或是上廁所）時，飲用牛奶（補水指數高于水和冰咖啡）才是個明智之選。但別忘了牛奶比水含有更多的卡路里，喝奶雖好，可不要貪杯噢。

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 compensate for their increased fluid losses,” Dr. Maughan said.
雖說除了劇烈運動、極端環境或是患病時，人們一般不會嚴重缺水，但研究顯示，炎熱天氣下的高溫脫水會提高死亡率。“在熱浪襲來時，死亡率往往會急劇攀升，這主要是因為人們沒有及時補充他們流失掉的水分。”莫恩博士說道。

Dr. Armstrong noted 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 refreshing drink.
莫恩博士指出，在高溫天氣下，人們非常有必要全天注意體內的含水狀況。他建議人們多注意自身的口渴狀況，必要時補充水分。此外，若是你的尿液已經呈現深黃色，是時候補充水分了。

英文來源：雅虎新聞
翻譯：陳蕾羽（中國日報網愛新聞iNews譯者）
編審：yaning