Harvard Heart Letter

Ask the doctor: Could a sudden gain in weight be caused by hot weather?

Q. At 80 years old, I am in relatively good health, aside from a recent diagnosis of high blood pressure. Taking a beta blocker and watching my salt has brought my blood pressure down into the normal range. During a period of extreme heat this summer, my ankles were more swollen than usual, and my weight jumped three pounds in just two days. Was that because of the heat, or did salt have something to do with it?

A. Congratulations on getting good control of your blood pressure with a medication and salt restriction. Most people require two or three medications to control high blood pressure, but you are a good example of what salt restriction can do.

The "salt" we are discussing is sodium. Along with chloride, sodium makes table salt. Sodium is the primary agent that regulates the fluid level in the bloodstream as well as the fluids that bathe cells. Rapid changes in weight — like three pounds in two days — are almost always caused by taking in too much sodium from foods and beverages.

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