[Aging and water metabolism in health and illness]

Normal aging is associated with changes in body composition, thirst perception, renal function, and the hormonal regulatory systems involved in the maintenance of water and sodium balance. The presence of many diseases and drugs common in the elderly can interact with the impaired homeostatic systems to result in clinically significant disturbances of water and sodium with accompanying symptoms, morbidity, and mortality. These disorders, which include dehydration, hypernatremia, hyponatremia, urinary frequency, and urinary incontinence can either be prevented or promptly recognized and appropriately treated by understanding the physiological changes and clinical circumstances which put the elderly person at increased risk for deranged water and sodium balance.