Harvard Health Letter

By the way, doctor: How can I avoid dehydration?

Q. What exactly is dehydration? It put me in the hospital after a mild flulike illness. How can I avoid it in the future?

A. It may come as a surprise, but your body is 50%–60% water. Each of your trillions of cells is about half water, and you also store water outside your cells — in your blood and in the spaces between your cells.

Dehydration is when the amount of water in your body gets too low. We get water from food and drinks, and we lose it through sweat, exhaled breath, urine, and feces. Many things can cause you to lose more water than usual, such as exercising in the heat, a bout of vomiting or diarrhea, a high fever that results in a heavy sweat (which can happen when you have the flu or something like it), or diuretic medicines. A mild case causes a little dizziness when standing up, weakness, and fatigue. More severe dehydration can cause seriously low blood pressure or even loss of consciousness.

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