運動不要多喝水? Sweating runners must check their salt intake

Endurance athletes such as runners and cyclists are used to hearing injunctions to drink enough water. While staying hydrated is important, there are times when you can have too much water.

跑步和自行車等耐力運動的運動員已習慣於聽到要補充足夠水分的勸告。儘管保持身體有足夠水分很重要，但有時候你可能會攝入過多的水分。

Last summer, for example, I began experiencing unusual muscle cramping in my hands and legs long after I finished a run, even the next day. Following the usual advice, I increased my water intake and ate bananas, which are full of potassium. That did not fix the problem. I then heard Jordan Metzl, a sports medicine specialist at the Hospital for Special Surgery in New York, describe how he had nearly crashed during his first Ironman race. It was a hot day, Dr Metzl recalled, and he was saved by a bearded bystander who was handing out raw salt.

比如，去年夏天，我開始在跑完步很長時間後（乃至第二天）出現手部和腿部肌肉痙攣。我遵循一般的建議增加了水分攝入，吃富含鉀的香蕉。然而問題沒有解決。之後我聽了紐約特殊外科醫院(Hospital for Special Surgery)運動醫學專家約爾丹•梅茨爾博士(Jordan Metzl)講述他在第一次參加鐵人三項賽時差點暈倒的事情。梅茨爾回憶，那天天氣炎熱，一個蓄着鬍鬚、正在分發粗鹽的旁觀者救了他。

If you follow medical news, you have probably heard the campaigns in the UK and the US warning about eating too much salt. It is true that there is often a lot of salt added to prepared food, and sodium can raise your blood pressure, which can lead to a heart attack.

如果你關注醫學方面的新聞，你很可能聽說過英美兩國旨在警告人們不要攝入太多鹽分的宣傳活動。的確，預製食品中往往含有大量鹽分，鈉可能會升高你的血壓，高血壓可能導致心臟病發作。

But cyclists and runners face an entirely different problem — too little salt, says Dr Metzl, who has run 30 marathons and is the author of a medical guide for athletes calledRunning Strong. When it is hot and humid, most people tend to sweat a lot during exercise. Very fit athletes actually sweat more than other people, which sounds counterintuitive, but it helps cool them down.

但梅茨爾表示，自行車運動員和跑步運動員面臨着截然不同的問題——鹽分攝入太少。梅茨爾參加過30次馬拉松比賽，著有爲運動員撰寫的醫學參考書《跑步者健康指南》(Running Strong)。天氣炎熱潮溼的時候，大多數人會在鍛鍊中大量出汗。身體非常健康的運動員實際上會比其他人出汗更多，這聽起來似乎有悖直覺，但這其實能夠幫助運動員降低體溫。

There is also a subgroup of athletes whom Dr Metzl calls “salty sweaters”, who not only sweat more than most during exercise but also sweat much more salt. I know because I am one and my sweat is so salty it sometimes irritates my skin.

在運動員中，有一類人被梅茨爾稱爲“多鹽流汗者”(salty sweaters)，這類人在鍛鍊中不僅會比大多數人出更多的汗，而且他們的汗液中含鹽量也大得多。對此我有親身體會，我的汗液中含鹽量很大，以至於有時候會刺痛我的皮膚。

A natural reaction when you sweat is to drink more water, especially during races when there are water tables by the roadside. But if you are taking in water and not electrolytes, which include sodium, magnesium and potassium, you are making the problem worse. The water dilutes the salt in your blood, which has been reduced by your sweat.

當你流汗的時候，自然反應是喝更多的水，尤其是在那種設置了路邊飲水桌的比賽期間。但如果你只攝入水，不攝入鈉、鎂、鉀等電解質，你會使問題變得更糟。水會稀釋你血液中本就因爲出汗而減少的鹽分。

Too little sodium in the blood can cause a condition known as hyponatraemia, which was only identified in 1985. Early symptoms of hyponatraemia are cramps of the small muscles in your hands and feet, like I had, followed by leg cramps. If the problem continues to worsen, you can become mentally disoriented and even, in extreme cases, die.

血液中鈉含量過低會導致一種叫做“低鈉血癥”的病症。人們直到1985年才發現這種病症。低鈉血癥的早期症狀是手腳小肌肉羣痙攣，就像我曾經經歷過的那樣，然後是腿部肌肉痙攣。如果症狀持續惡化，你可能會神志不清，在極端情況下甚至可能死亡。

The British Journal of Sports Medicine looked at the problem and urged endurance athletes to ensure they get enough salt during exercise, but also warned that “electrolyte replacement will slow but not prevent the development of hyponatraemia if fluid intake is in gross excess of sweating rate”. In other words, do not drink too much.

《英國運動醫學期刊》(British Journal of Sports Medicine)研究了這個問題，並敦促耐力運動員確保他們在訓練時攝入足夠的鹽分，但這份期刊還警告稱，“如果液體攝入總量超過出汗量，補充電解質只能減緩、但無法阻止低鈉血癥的形成”。換句話說，不要喝太多水。

Unfortunately, many of the commercial brands of electrolyte-laden sports drinks are loaded with sugar, which is counterproductive if you are running to stay in shape. Luckily there are electrolyte tablets like High5 Zero and Nuun available that contain sodium but no sugar. Take them well before you start your endurance event and after as well.

遺憾的是，很多商業品牌的電解質運動飲料都含有大量的糖，如果你跑步是爲了保持身材，喝這種飲料會適得其反。幸運的是，現在有High5 Zero、Nuun這樣含鈉但不含糖的電解質片劑。你要在開始耐力運動之前和之後服用這類片劑。

Some people may worry about raising their blood pressure by taking electrolytes; indeed, people with a heart condition should consult their doctor before taking them. But Dr Metzl says that for most endurance athletes, having too little salt in the blood poses a far greater risk than having slightly higher blood pressure for a day or two.

有些人可能會擔憂，攝入電解質可能會升高血壓；的確，患有心臟疾病的人士應該在服用前諮詢他們的醫生。但梅茨爾表示，對於大多數耐力運動員而言，比起血壓在一兩天內略微升高，血液中鹽分太少造成的威脅要大得多。