Introduction:
Water is essential for the body to function correctly. About sixty to seventy percent of the body weight is water, and every part of the body needs water to perform its task correctly. For example, water helps the kidneys remove toxins and waste products from the blood through urine. It also allows the blood vessels to easily pass blood to the kidneys and supply them with nutrients.
What Is Water Homeostasis?
Homeostasis means the steady state of internal, external, physical, and chemical conditions maintained by living organisms. The kidneys play a pivotal role in maintaining water homeostasis. Water homeostasis is achieved by the regulation of intake and loss of water by the kidneys. Every day, the kidneys produce one hundred fifty liters of urine. The body reabsorbs ninety percent of this urine. Reabsorption of the remaining ten percent depends upon the hormone vasopressin. Water homeostasis is maintained by thirst sensation and the antidiuretic hormone vasopressin. Vasopressin is a hormone that is secreted by the pituitary gland. It acts on the kidneys causing water reabsorption from the kidney tubules, thus preventing water loss and dehydration. Around one percent of the initial amount of urine produced is excreted from the body as urine. The kidneys work efficiently with excess water. However, when there is an insufficient fluid intake, the kidneys reabsorb water by concentrating the urine. Even mild dehydration can tire one, impairing the body's normal functioning. Severe dehydration can result in kidney damage; thus, it is crucial to maintain water homeostasis through regular water intake.
What Are the Limits of Kidney Water Regulation?
The kidneys have a tremendous capacity to handle water. Water preservation is essential in a dry environment, so as the body's water content falls, the brain starts to secrete the vasopressin hormone as the body's water content falls. This hormone is stored within the pituitary gland unless needed. Vasopressin causes the reabsorption of water from the urine, making it concentrated. If the amount of water required to remove the waste is insufficient, it will worsen the condition of dehydration. If the fluid deficiency is in excess, the blood flow to the kidneys is impacted. If this reduction is severe, it might cause a collapse of the kidneys' filtration system, signifying a loss of kidney function and water homeostasis.
In contrast, the kidneys can easily remove excess water from the body. This is because excess water inhibits the secretion of the vasopressin hormone from the pituitary gland. In the absence of vasopressin hormone, the kidney cells become impermeable, allowing the removal of a large amount of water. Thus, drinking a volume of water that reasonably exceeds the body's requirement is not harmful and would not drastically change the total water volume in healthy individuals. This proves that the kidneys can manage excess fluid intake much more efficiently than deficient ones.
What Are the Effects of Increased Water Intake on the Kidneys?
The common myth is that drinking large amounts of water would help eliminate more waste. Smith proposed that kidney function is related to the glomerular filtration rate. The glomerular filtration rate determines how well the kidneys work. The glomeruli are a bunch of tiny filters in the kidneys that help remove waste and excess water from the body. As long as the extracellular volume (fluid volume outside the body's cells) is adequate to maintain the kidney blood flow, the amount of water made available by the glomerular filtration will allow healthy kidney function. Whereas a sharp reduction in the total body water hampers the
Kidney function. The period between water intake requires the body to save water by concentrating the urine. This situation arises when an individual waits to be thirsty before drinking water. At that time, the total body water has already decreased. When the individual is thirsty, the increased vasopressin concentration stimulates maximum kidney concentration. Therefore, being thirsty indicates that one is mildly dehydrated. A little dehydration increases the risk of developing kidney stones and urinary tract infections.
Is an Increase in Water Intake Beneficial?
Several epidemiological studies have found that low urine output risks developing kidney stones. Pak et al., thirty years ago, also found that an increase in water intake increases urine output, thereby reducing the chances of developing kidney stones. In Western countries, the prevalence of kidney stones is around ten percent of the population, and half of these cases reoccur.
Two studies have been carried out by Danone Research to evaluate the benefit of increasing the water intake for healthy people. One of the studies was performed in Spain and another in Mexico. These were randomized studies carried out on forty-eight healthy volunteers from both countries. It had equal participation from both sexes, with ages ranging from twenty-five to fifty years. The experiment asked the volunteers to drink two liters of water for six consecutive days. The main result was a change in chronic renal insufficiency or CRI in the first-morning urine and twenty-four-hour samples.
The effectiveness of the experiment was assessed by checking twenty-four-hour urine volume. The mean volume of urine in the volunteer group was significantly increased. This was because the participants increased their water intake but reduced the information on other fluids.
Against the myth that drinking water removes excess waste, increasing the intake by two liters did not have any change in the waste removal. The urine constituents such as urea, uric acid, creatinine, sodium, potassium, calcium, chloride, oxalate, and citrate remained unchanged.
Conclusion:
The kidneys are the critical organs of water homeostasis. It removes excess water to maintain water homeostasis. The kidney's capacity to manage excess water exceeds the kidney's ability to save water during dehydration. Thus slight dehydration is common. Despite different studies and experiments that tried to determine the impact of dehydration, it is challenging to differentiate optimal hydration from slight dehydration. It can be assumed that drinking enough water provides sufficient fluid to maintain the total volume of water in the body. It should also dilute the waste products to reduce the risk of developing urinary tract infections and kidney stones. Drinking the amount of water that safely removes the waste products is more significant than drinking only when thirsty. The urine concentration detects hydration early as it shows the body's water balance.
