In a recent review article published in Nature Reviews Nephrologyresearchers synthesized what is known about the long-term consequences of chronic underhydration.
Most people know that hydration is vital to maintaining health, but studies show that insufficient hydration is a common problem, affecting nearly half of adults surveyed in the United States and Europe. Experts believe that it is exacerbated by the lack of inclusion in health guidelines and reinforcement by doctors during preventive examinations.
Although the short-term effects of acute dehydration are widely recognized, less clinical attention has been paid to the long-term effects of chronic underhydration.
Epidemiological studies now show that even mild but chronic underhydration can lead to the development of coronary heart disease, heart failure, diabetes, obesity, deterioration of kidney function, premature mortality and faster aging. These findings were reinforced by observing mice subjected to chronic water restriction.
Review: Long-term health outcomes associated with hydration status. Image credit: Love the Wind / Shutterstock
Adaptive responses to insufficient hydration
Homeostasis is the state of balance between all body systems necessary for the body to survive and function properly, and water balance is a key mechanism by which this occurs. Osmoregulation, or the control of water and salt balance, is known to provide an osmotically stable environment for many cells.
Insufficient hydration leads to adaptive changes throughout the body. At all times, water losses through respiration, gastrointestinal tract, sweat, and urine must be balanced against water gains through food and fluid ingestion.
The body must maintain a stable composition and volume of intracellular fluids (ICF) and extracellular fluids (ECF); changes in the water content of the body, due to excess or deficiency, affect all organs, tissues and cells.
One response to a deficit in water balance is the release of the antidiuretic hormone arginine vasopressin (AVP), which reduces water loss through excretion. Vasoconstriction, stabilization of blood pressure and increased heart rate occur, while water reabsorption is facilitated.
Sensations of thirst and salt appetite are also stimulated by AVP and angiotensin II (ANGII). However, thirst regulation or prior inhibition acts to prevent binge drinking; thirst responses may also decrease with age. Sweating is also reduced, which can lead to compromised thermoregulatory responses in hot conditions and cause chronic kidney disease.
Over time, chronic underhydration can establish a new steady state of water balance, matching water losses with water intake. This reaction can be triggered under conditions where access to water is limited. Over time, this can lead to deterioration of physiological systems, but these mechanisms are poorly understood.
Diseases associated with insufficient hydration
Researchers believe that underhydration, or hypohydration, is a moderate decrease in water levels in the body that results in the activation of water conservation mechanisms so that normal levels of plasma osmolality and sodium can be maintained. This contrasts with dehydration, a condition in which water conservation mechanisms are unable to maintain water balance.
Acute water loss is most visible in military personnel and athletes, increasing heart rate and reducing the efficiency of anaerobic exercise. Acute dehydration can also adversely affect cognitive functioning, including alertness, concentration, short-term memory, and visual perception.
Certain diseases and conditions are thought to predispose people to insufficient hydration. For example, uncontrolled diabetes mellitus can lead to water loss because it reduces renal reabsorption of water. Increased urine output can result from nephrogenic diabetes insipidus and some forms of polycystic kidney disease. Conversely, certain cancers and drugs can also stimulate AVP secretion without low water intake, leading to hyponatremia.
Interventions to increase hydration
In response to emerging evidence regarding the adverse effects of insufficient hydration, researchers have begun to investigate whether optimal hydration can prevent or delay metabolic and cardiovascular disease.
Interventions that focused on regimens designed to increase water intake found that participants faced barriers such as forgetting to drink, lack of access, lack of thirst, dislike of the taste of water, and not appreciating the benefits of proper hydration; another problem is work-related interference as a result of increased urinary frequency.
These challenges were demonstrated through an experiment that found lower adherence to water intake regimens compared to a control liquid of inactive syrup.
One study that successfully increased hydration in the intervention group found that higher water intake was significantly associated with reduced copeptin levels among people with chronic kidney disease. Another found that the biggest changes were seen in people who habitually drank little.
Conclusions
The literature has identified associations between markers of chronic underhydration and increased risk of several chronic diseases, but the mechanisms underlying these phenomena are not well understood. There are indications that hydration may be a preventive tool, but causal inferences are limited by lack of adherence to hydration regimens.
However, even with these limitations, there is evidence that optimal hydration may benefit people who habitually drink little. Future studies on the efficacy of interventions to increase water intake should monitor compliance more closely and continue to focus on chronically underhydrated populations that stand to gain the most.
