Seems as though dysregulated thirst plays a big role, e.g. 90% of the issue is resolved if habitual fluid intake is simply increased to what it once was. Kidneys may play a role, as does, I suspect, poor circulation[1] and poor osmosis or altered ion exchange thru semi-permeable membranes[3], [4].
It could also be related to excessive sodium and/or potassium deficiency, which itself is a risk factor in cardiovascular disease.
Dehydration and Aging
Dehydration occurs when your body doesn’t have enough water and other fluids to function normally. Dehydration can happen to anyone, but it is a problem that is more common in people who are older.
Your body loses water every day when you breath, perspire, urinate, and have bowel movements. For your body to work right, you need to keep it well hydrated.
As you age, your sense of thirst lessens and the kidney isn’t able to conserve body water as well. Over the age of 50, you may feel tired and draggy rather than thirsty, and may opt for a nap instead of a tall glass of water. If you remain dehydrated, you can end up suffering complications, some of which can be serious.
Drugs Can Dry You Out
Medications — not only diuretics that make you urinate more water, but also drugs for blood pressure and other cardiac conditions — can compound the effect of dehydration on blood pressure.
These medications are usually taken first thing in the morning and reach their peak effect in the late morning. Sometimes eating a meal high in salt can shift body fluid to the stomach and intestine to aid digestion, which is a perfect recipe for making you faint if you are already dehydrated.
Other, more serious, complications may include heatstroke, swelling of the brain, seizures, kidney failure, and, if you become severely dehydrated, even death.
Symptoms
For mild dehydration look out for:
Dry, sticky mouth
Sleepiness or tiredness
Thirst
Decreased urine
Headache
Lightheadedness
Severe dehydration, which is a medical emergency, may cause:
Extreme thirst
Irritability and confusion
Very dry mouth, skin, and mucous membranes
Lack of sweating
Little or no urination
Low blood pressure
Rapid heartbeat
Fever
Delirium or unconsciousness
Thirst sometimes is not a good gauge of how much water your body needs, especially for older adults. A better way to check is to look at the color of your urine: clear or light-colored urine means you’re getting enough water, and dark yellow urine may mean you’re dehydrated.
Dehydration Prevention
The best way to prevent dehydration is to make sure you drink enough water and eat plenty of foods high in water content such as fruits and vegetables. Also remember that your body needs more water if you live in a hot climate, you are sick, or you are exercising.
The Centers for Disease Control recommends adults drink almost 2 liters of water a day — that’s about eight 8-ounce glasses. The Institute of Medicine recommends adults drink 3.7 liters of water a day (or roughly 15 8-ounce glasses daily).
Most doctors recommend drinking eight or nine glasses of water a day. If you have a chronic medical condition, such as congestive heart failure, talk to your doctor first about how much fluid you require.
Anytime you are feeling faint, tired, or dizzy, don’t just go lie down. Consider that your body is trying to tell you something — and it could be that it’s thirsty. Go get a glass of water. It could change your whole day!
- See more at: http://www.johnmuirh...h.HTjDAAU3.dpuf
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Brain-Imaging Study Tries to Discover Why We Lose Our Sense of Thirst as We Age
SAN ANTONIO -- The sense of thirst declines as people age, a phenomenon that can be especially dangerous for the elderly during the summer.
Scientists in Texas and Australia are collaborating on a study to find out what happens in the brain that causes the sense of thirst to wane.
“Many elderly people should feel thirsty, but they don’t, and because they’re not thirsty, they don’t drink enough liquids,” said Dr. Robert Shade, associate scientific director and chairman of the Department of Physiology and Medicine at the Southwest Foundation for Biomedical Research, based in San Antonio. “As a result, they can become volume depleted or dehydrated.”
Shade said that may be one significant reason why the elderly are more adversely affected by heat stress, which can send many to the hospital for emergency medical care and even lead to death, as was seen in the summer 2003 heat wave in France that killed thousands.
Currently, scientists and physicians do not understand why people’s sense of thirst declines with age. One strong possibility is a “cognitive disconnect.” As cognitive function declines with aging, it may be that something goes awry in the process of how a physical stimulus sends a signal to the brain and the brain interprets that signal to elicit the appropriate response. But where does that disconnect occur? And what exactly is causing it? That still needs to be determined.
“Clearly, either many elderly people are not aware of being thirsty – at least not to the degree they should be – or if they are aware of it, it isn’t registering correctly and they’re misinterpreting the symptoms,” said Dr. Peter Fox, director of the Research Imaging Center, the University of Texas Health Science Center at San Antonio. “Perhaps they’re uncomfortable, but they can’t put their finger on why. So it’s not clear what exactly is going on, but it is clear that when you lose the urgency of your thirst drive, you die. So this is a big risk.”
Shade and Fox are working with Dr. Derek A. Denton, emeritus research professor and emeritus director, the Howard Florey Institute for Experimental Physiology and Medicine, The University of Melbourne, Australia. A grant to the Florey Institute from the G. Harold and Leila Y. Mathers Charitable Foundation, New York, is funding the thirst study.
For 15 years, Drs. Shade and Denton have collaborated on animal studies exploring the physiology of salt-and-water metabolism and salt-and-water appetite. In 1997, they teamed up with Dr. Peter Fox, with resources and expertise in brain imaging and an understanding of the brain mechanisms of physiology and cognition. With their combination of expertise and resources, these researchers were in a unique position to explore the physiological interaction of cerebral function and the autonomic nervous system, particularly as it relates to thirst.
They have conducted several studies of a “normal” population, healthy young adults, who agreed to undergo PET scans of their brains while experiencing different levels of thirst. These studies served to document which areas of the brain are activated as the need for fluids increases and decreases; the strength of brain signals and their reception in areas of the brain related to perception, attention and cognition; and which areas of the brain are affected by either thirst, physical stress, or both.
Now that they have the data from younger adults, the investigators are recruiting an equal number of healthy senior citizens, age 65 and up, to participate in the same study. Researchers can then compare their brain scans to those of their younger counterparts and hopefully identify parts of the thirst-signaling mechanism that are not working properly in the elderly.
“We’re going to look at where in the brain signals are getting lost as the brain first receives a signal from a thirst stimulus, then transfers that signal to the area of the brain where consciousness lies,” said Dr. Shade. “We also will look at differences in the degree of brain activation in the elderly as compared to young people. Perhaps we’ll see that the right areas of the brain are activated in the elderly, but the degree of that activation is less. That would be very informative. It would give us a clue to where the differences lie and what the problem is.”
From there, researchers expect that follow-up studies in animals will be needed to learn more about the physiological factors causing the breakdowns in the thirst mechanism, as well as how to design treatments to correct that breakdown.
https://en.wikipedia.org/wiki/Thirst
Osmometric thirst occurs when the solute concentration of the interstitial fluid increases. This increase draws water out of the cells, and they shrink in volume. The solute concentration of the interstitial fluid increases by high intake of sodium in diet or by the drop in volume of extracellular fluids (such as blood plasma and cerebrospinal fluid) due to loss of water through perspiration, respiration, urination and defecation. The increase in interstitial fluid solute concentration causes water to migrate from the cells of the body, through their membranes, to the extracellular compartment, by osmosis, thus causing cellular dehydration.
Clusters of cells (osmoreceptors) in the organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO), which lie outside of the blood brain barrier can detect the concentration of blood plasma and the presence of angiotensin II in the blood. They can then activate the median preoptic nucleus which initiates water seeking and ingestive behavior.[1] Destruction of this part of the hypothalamus in humans and other animals results in partial or total loss of desire to drink even with extremely high salt concentration in the extracellular fluids.[5][6]
In addition, there are visceral osmoreceptors.[4] These project to the area postrema[4] and nucleus tractus solitarii[4] in the brain.
Osmoreceptor Function among the Elderly
The osmoreceptor function of six elderly patients of both sexes and of ages varying between 65 and 91 years has been investigated. It was observed that in three patients there was practically no osmoreceptor response to the challenge of fluid deprivation. In two patients the response was subnormal, and only one out of six cases showed a normal response. The clinical significance of these observations is discussed. As it is a pilot study, further work should be done in this field to clarify the matter.
Water-loss dehydration and aging.
This review defines water-loss and salt-loss dehydration. For older people serum osmolality appears the most appropriate gold standard for diagnosis of water-loss dehydration, but clear signs of early dehydration have not been developed. In older adults, lower muscle mass, reduced kidney function, physical and cognitive disabilities, blunted thirst, and polypharmacy all increase dehydration risk. Cross-sectional studies suggest a water-loss dehydration prevalence of 20-30% in this population. Water-loss dehydration is associated with higher mortality, morbidity and disability in older people, but evidence is still needed that this relationship is causal. There are a variety of ways we may be able to help older people reduce their risk of dehydration by recognising that they are not drinking enough, and being helped to drink more. Strategies to increase fluid intake in residential care homes include identifying and overcoming individual and institutional barriers to drinking, such as being worried about not reaching the toilet in time, physical inability to make or to reach drinks, and reduced social drinking and drinking pleasure. Research needs are discussed, some of which will be addressed by the FP7-funded NU-AGE (New dietary strategies addressing the specific needs of elderly population for a healthy ageing in Europe) trial.
Influence of age on thirst and fluid intake.
Independently living older adults (over the age of 65 yr) consume adequate volumes of fluids on a daily basis. However, when challenged by fluid deprivation, a hyperosmotic stimulus, or exercise in a warm environment (all of which combine hypovolemia and hyperosmolality), older adults exhibit decreased thirst sensation and reduced fluid intake. Full fluid restoration eventually occurs, but full restoration of fluid balance is slowed. The aging process alters important physiological control systems associated with thirst and satiety. Recent evidence suggests that older men and women (i) have a higher baseline osmolality and thus a higher osmotic operating point for thirst sensation (with little or no change in sensitivity), and (ii) exhibit diminished thirst and satiety in response to the unloading (hypovolemia) and loading (hypervolemia) of baroreceptors. A diminished sensation of thirst in the elderly relative to young adults is generally absent when a volume stimulus is absent, despite higher baseline plasma osmolalities. Compared with the elderly, there are scant data associated with homeostatic control of thirst in children. Nonhomeostatic control of thirst and drinking behavior may likewise be different for children (as it is for the elderly), as compared with young adults; however, little empirical data exist on this topic. Children rarely exhibit voluntary dehydration for activities lasting 45 min or less; however, drink flavoring and sodium chloride are important promoters of drinking in active children.
