Older adults are at greater risk for dehydration due to which physiologic change?

• A. Reduction of muscle mass and amount of body water
• B. Increased subcutaneous fat
• C. Higher metabolic rate
• D. Enhanced thirst sensation

Answer: (A)

Older adults become more prone to dehydration mainly because lean body mass—and with it total body water—declines with age. Muscle is a major reservoir of water, so as muscle mass decreases, the body's overall water content drops, leaving less reserve to draw on during fluid losses from illness, heat, or inadequate intake. While other age-related changes can worsen dehydration—such as reduced kidney concentrating ability and a blunted thirst response—the key physiologic change driving the risk is the loss of muscle mass and the accompanying reduction in body water. Increased fat tissue holds less water, so more fat doesn’t help hydration; metabolic rate often decreases with age and doesn’t explain higher dehydration risk; and thirst sensation is typically reduced, not increased, in older adults.