Merck Manual

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Spotlight on Aging: Water Balance

Spotlight on Aging: Water Balance


Older people are particularly susceptible to dehydration. In older people, common causes of dehydration include

  • Confusion

  • Disorders that make obtaining fluids difficult (usually because of restricted mobility, such as after a stroke)

Additionally, older people sense thirst more slowly and less intensely than younger people do, so even those who are otherwise well may not drink enough fluids for a variety of reasons, including incontinence or the fear of incontinence.

Older people have a higher percentage of body fat. Because fat tissue contains less water than lean tissue, the total amount of water in the body tends to decrease with age.


In overhydration, the body contains too much water. In older people, the kidneys excrete excess water less efficiently, and thus older people can develop overhydration more easily than younger people do. Swelling may or may not occur.