Impact of Aging on Water Metabolism
17/01/11 09:09
Impact of Aging on Water Metabolism
The age-related decrease in total-body water (relative and absolute) makes elderly persons markedly susceptible to stresses on water balance. Average healthy 30- to 40-year-old persons have a total-body water content of 55 to 60 percent. By age 75 to 80 years, the total-body water content has declined to 50 percent, with even more of a decline in elderly women.
Clearly, the thirst mechanism diminishes with age, which significantly impairs the ability to maintain homeostasis and increases the risk for dehydration. There is also a clear age-related decrease in maximal urinary concentrating ability, which also increases the risk for dehydration. ADH release is not impaired with aging, but ADH levels are increased for any given plasma osmolality level, indicating a failure of the normal responsiveness of the kidney to ADH.
The ability to excrete a water load is delayed in the elderly. This propensity may contribute to the frequently observed episodes of hyponatremia in hospitalized elderly patients who are receiving hypotonic intravenous fluids or whose fluid intake is not properly monitored.
Other changes in renal physiology and anatomy that increase the elderly patient's susceptibility to alterations of water imbalance include decreased renal mass, cortical blood flow and glomerular filtration rate, as well as impaired responsiveness to sodium balance.
The impact of a lifetime of accumulated disease and comorbidities must also be duly considered in every clinical situation with an elderly patient, in addition to age-related physiologic changes. The elderly patient has a diminished reserve of water balance and an impaired regulatory mechanism. Thirst sensation, concentrating abilities and hormonal modulators of salt and water balance are sluggish and highly susceptible to being overtaken by morbid or iatrogenic events.
Original article: http://www.aafp.org/afp/20000615/3623.html
The age-related decrease in total-body water (relative and absolute) makes elderly persons markedly susceptible to stresses on water balance. Average healthy 30- to 40-year-old persons have a total-body water content of 55 to 60 percent. By age 75 to 80 years, the total-body water content has declined to 50 percent, with even more of a decline in elderly women.
Clearly, the thirst mechanism diminishes with age, which significantly impairs the ability to maintain homeostasis and increases the risk for dehydration. There is also a clear age-related decrease in maximal urinary concentrating ability, which also increases the risk for dehydration. ADH release is not impaired with aging, but ADH levels are increased for any given plasma osmolality level, indicating a failure of the normal responsiveness of the kidney to ADH.
The ability to excrete a water load is delayed in the elderly. This propensity may contribute to the frequently observed episodes of hyponatremia in hospitalized elderly patients who are receiving hypotonic intravenous fluids or whose fluid intake is not properly monitored.
Other changes in renal physiology and anatomy that increase the elderly patient's susceptibility to alterations of water imbalance include decreased renal mass, cortical blood flow and glomerular filtration rate, as well as impaired responsiveness to sodium balance.
The impact of a lifetime of accumulated disease and comorbidities must also be duly considered in every clinical situation with an elderly patient, in addition to age-related physiologic changes. The elderly patient has a diminished reserve of water balance and an impaired regulatory mechanism. Thirst sensation, concentrating abilities and hormonal modulators of salt and water balance are sluggish and highly susceptible to being overtaken by morbid or iatrogenic events.
Original article: http://www.aafp.org/afp/20000615/3623.html
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