What To Drink When Exercising In The Heat

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DEAR DR. DONOHUE: I am taking my two teenage boys backpacking in the Southwest this August. It will be hot and dry, and I am preparing for those conditions. I need some guidance on what fluids to drink. I was taught that drinking plain water is the best way to stay hydrated. My older son says his class was told not to drink plain water, because it could cause brain damage. What is this all about? — F.W.

ANSWER: It’s all about becoming sodium-depleted and having the brain swell as a result. The condition is hyponatremia.

It used to be taught that, when exercising in hot weather, people should guzzle water at every opportunity, even when they don’t feel thirsty. That can be dangerous if the exercise lasts for hours and hours and if the only liquid drunk is water. Too much water dilutes body sodium. That, in turn, can cause brain swelling and, in the extreme, death.

Up-to-date advice is to let thirst be a rough guide for how much liquid you drink. If people are engaged in prolonged exercise, it is good to include some salt in the program. Half a teaspoon of salt and half a teaspoon of baking soda (sodium bicarbonate) in a quart of water can keep body sodium levels from dropping. For you and your sons, it would be advisable to salt your food and to eat some salty snacks — another way to ensure body sodium doesn’t bottom out.

Hyponatremia is uncommon. Dehydration is common. For most, drinking water as a replacement fluid in hot weather is fine. It’s not going to lead to a dangerous drop in body sodium. Only those who lose lots of sweat for long periods of time run the risk of hyponatremia by drinking pure water.

This is advice that doesn’t apply only to athletes or backpackers. It applies to all those who are out working in hot weather and sweating up a storm.

DEAR DR. DONOHUE: I have hypertension, and I go to the beach often. Can salt in salt water get through the skin as medical patches get through the skin? My doctors have increased my dose of medicine and have added additional medicines without much improvement in my blood pressure.

Could the salt water I swim in be keeping my blood pressure high? — G.S.

ANSWER: G.S., I know I answered this question before, but you must not have seen it. I’ll do it again.

The salt in salt water doesn’t get through your skin. Swimming in salt water doesn’t raise blood pressure. It improves it. All exercise does.

If you miss the answer this time, G.S., I have to drop the question. People will think I’m obsessed with it.

The booklet on hypertension provides more details on this epidemic illness. Readers can obtain a copy by writing: Dr. Donohue — No. 104W, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Canada with the recipient’s printed name and address. Please allow four weeks for delivery.

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.

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