Effects of Aging

The very young (especially premature infants) and the very old are more susceptible to disturbances in water balance. In both groups, the kidneys may function less well than during the rest of life. Thus, premature infants can very easily become dehydrated, usually due to diarrhea. They may become overhydrated if they receive too large an amount of intravenous fluids.

Older people are particularly susceptible to dehydration. In older people, common causes of dehydration include confusion and disorders that make obtaining fluids difficult (usually because of restricted mobility). Additionally, older people sense thirst more slowly and less intensely than younger people do, so those who are otherwise well may not drink enough fluids. Also, 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.