In Hot Weather, How Much Water Is Enough?

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DEAR DR. DONOHUE: I am confused about how much water to drink when exercising in hot weather. I learned that you should drink all the time during exercise, even when you aren’t thirsty. Now they tell me that drinking too much affects your brain and can cause death. What’s the story here? — M.F.

ANSWER: This has to be one of those “it depends” answers. How much water or any other fluid is needed in hot water depends on how hard is the exercise, how long you do it, how heavily you sweat, how hot it is and how acclimatized you are to heat. It takes two weeks to acclimatize to heat. After two weeks, less sodium and potassium are lost in sweat.

Formerly, the advice for fluids was to drink frequently even if you didn’t feel thirsty. That’s overkill. You can let thirst be your guide most of the time. Older people have a somewhat blunted thirst sense, so they might have to remind themselves to drink in exceptionally hot weather.

To stay hydrated during heavy physical activity or exercise, drink 12 to 16 ounces of fluid three to four hours before exercise. The fluid can be plain water. It’s also a good idea to take a salty snack before exercise — pretzels, peanuts or crackers.

During activity, drink about every 20 minutes, as much as your thirst tells you.

If your activity lasts longer than two or three hours and if you sweat heavily, then you have to pay attention to your salt intake. Marathon runners taught us this. A few marathoners died from drinking only water during hot-weather races. Doing so lowers body sodium. That’s hyponatremia, and it can be serious. Headache, vomiting, swollen ankles and feet, fatigue far out of the fatigue usually felt and disorientation are some of the signs of hyponatremia.

Sports drinks with sodium in them can prevent hyponatremia. You can make your own replacement fluid by adding 1 tablespoon sugar, 1/8 teaspoon salt and 1 tablespoon orange juice to an almost-filled 8-ounce glass of water. You have to make enough to last for the whole exercise session.


DEAR DR. DONOHUE: My right ear began to throb so bad that I had to see a doctor. She said I have otitis externa, and gave me prescriptions for eardrops and pain medicine. She didn’t say much to me about this. She was in a hurry to see other patients. Will you explain to me what otitis externa is? — P.P.

ANSWER: It’s an infection of the ear canal, that small tunnel (about 1 inch long) that runs from the external ear to the eardrum. It’s the place where wax forms. Infections of the canal come about for a variety of reasons. They always hurt, and they sometimes cause a foul drainage.

Be sure to use the eardrops — which, I’m sure, are antibiotic drops — for as long as the prescription says to. Don’t stop when the pain leaves, or the infection can return.

I know what you mean about the doctor being busy. Managed care has doctors on such tight schedules that the doctor-patient relationship is often lost.


Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.

© 2010 North America Synd., Inc.

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