Total body water decreases with age.
Total body water manifests a linear decrease with aging, until it constitutes less than 50% of body weight in very old individuals. There is thus a mean decrease of 0.3 liter in total body water during the period of life from adulthood to old age.
Venous and Arterial Catheterization and Fluid Therapy
The ECFV (interstitial fluid + blood) is approximately 40% of TBW in neonates, decreasing to approximately 30% by 24 weeks of age. Generally estimated values of 30% (0.3 × TBW) for adults and 40% (0.4 × TBW) for foals are used for calculating fluid requirements.
The elderly have a reduced capacity to excrete a water load, which means they are predisposed to water overload and hyponatremia. Furthermore, various neuroendocrine changes in the elderly affect fluid and electrolyte homeostasis.
The decline of TBW with age is due primarily to a decline in ICW. The hydration of the FFM increased with age for the overall population because of a decline in TBK and TBN and an increase in ECW.
Hypernatremia and hyponatremia are the most common electrolyte abnormalities found in the elderly and both are associated with a high mortality.
With aging, the secretion of antidiuretic hormone during the night declines to maintain a similar level during the day and night, and this lack of difference becomes the major cause of adult nocturia [8].
As we age, it decreases to 50-55% and body fat increases. This lower level of body fluid, a reduced ability to conserve water and a diminished thirst sensation make seniors more susceptible to dehydration – which occurs when you lose more fluid than you take in.
Total body water decreases with age. In a younger man near his ideal body weight, total body water composes 60% to 65% of his body mass. By age 80 years, this contribution is reduced to 50%.
Variation due to Age
Neonates contain more water then adults: 75-80% water with proportionately more extracellular fluid (ECF) then adults. At birth, the amount of interstitial fluid is proportionally three times larger than in an adult. By the age of 12 months, this has decreased to 60% which is the adult value.
Appetite and thirst tend to diminish with age. This means that even when your body is craving fluids, you might not be aware of it—and you may drink less than you need to stay healthy. Older adults experience body composition changes over time that leave them with less water in their bodies to start with.
[1] The majority of fluid loss occurs in urine, stool, and sweat but is not limited to those avenues. Insensible fluid loss is the amount of body fluid lost daily that is not easily measured, from the respiratory system, skin, and water in the excreted stool.
Generally, an adequate intake (AI) of fluid for older adults is defined as 2.0 L/day for women and 2.5 L/day for men [6, 9]. Assuming 20% of fluids come from eating foods, this means women need at least 1.6 L/day of drinks and men 2.0 L/day.
Experts generally recommend that older adults consume at least 1.7 liters of fluid per 24 hours. This corresponds to 57.5 fluid ounces, or 7.1 cups.
Steps to Take to Get Enough Water. You should aim for 6 to 8 glasses of fluid a day. Here are some simple tips for making sure you reach your goal and get enough water. Sip on drinks throughout the day.
The recommended daily water intake is at least one cup of water for every 20 pounds of weight. If living in a warm climate, seniors might perspire and need more water. Exercise also increases the need for water as does medications and health conditions.
As a result, the reabsorption of water from the glomerular filtrate is increased. When someone drinks lots of water, requirement of absorption of water decreases, so ADH release is suppressed.
Blood pressure, hypertension, and exercise
An increase in osmolarity of the blood is a trigger prompting the hypothalamus to release ADH, which signals cells in the kidney tubules to reabsorb more water by inserting aquaporins, thus preventing additional fluid loss in the urine.
The kidneys are essential for regulating the volume and composition of bodily fluids. This page outlines key regulatory systems involving the kidneys for controlling volume, sodium and potassium concentrations, and the pH of bodily fluids.
Older patients are more likely to develop fluid imbalances. The management goals are to treat the underlying disorder and return the extracellular fluid compartment to normal, restore fluid volume, and correct any electrolyte imbalances.
Main points: Older people are more susceptible to dehydration than younger people. This is partly due to lack of thirst sensation and changes in the water and sodium balance that naturally occur as people age.