Water is our most important nutrient and the only one whose absence will be lethal within days. Getting enough water every day is important for your health and keeping fluid in the body at an optimum level is an intricate balancing act, which forms part of the body’s self-regulating processes to maintain internal stability, referred to as homeostasis. Apart from fluid balance, homeostasis applies to many other processes, such as body temperature and blood sugar balance.
The importance of water balance:
Water is a combination of hydrogen and oxygen and is the basis of all fluids in the body. Water makes up more than two thirds of the weight of the human body and all the cells and organs need water to function. Water also serves as a lubricant, as it makes up saliva and forms part of the fluids surrounding the joints. The body’s temperature is regulated by water through perspiration. Water helps to move food through the digestive system and prevents constipation. Without enough water each day, the fluids in the body will be out of balance and cause dehydration, which can be life threatening in severe cases.
An adult will on average take in about 2 500 ml of aqueous fluids through the digestive tract. About the same amount of fluid leaves the body daily, mostly removed as urine, but also through stool, sweating, and breathing. The kidneys regulate water levels in the body, for example by conserving water when you are dehydrated, or by making urine more diluted to expel excess water when necessary.
Although hydration levels affect the volume of urine, the body requires the production of a minimum volume of urine for proper bodily functions. The kidneys produce an average of 1,5 liters of urine daily to rid the body of excess salts and other liquid chemical waste products, such as creatine, urea, and uric acid. When low hydration levels result in too low levels of urine being produced (less than 0,5 liter), it means that metabolic waste products cannot be effectively removed from the body, which can impair the functioning of organs.
High hydration levels, such as drinking a large quantity of fluid, trigger the kidneys to compensate by producing urine in excess of normal levels, a process called diuresis.
Water’s journey starts when it is ingested through the mouth and the body registers hydration. After a few gulps the brain will tell the body that you have had enough to drink. This happens prematurely, as it takes a long time for water to reach the cells and provide them with sufficient hydration. Should the brain wait for cells to signal hydration, you would be drinking much more fluids than what the body needs. This communication between the mouth and the brain indicates when you should stop drinking.
How water balance affects the bloodstream:
The saying goes that blood is thicker than water when it comes to family. However, when the blood becomes too thick, or too thin, things start to go wrong for the family of cells, tissue, and organs in the body.
Drinking too little water and other fluids, or drinking too much, affects the viscosity of the blood, referred to as plasma osmolality – the ratio of solutes to water in blood plasma. The majority of water intake is absorbed through the walls of the small intestine into the bloodstream and will travel to cells across the body, to provide cells with the necessary hydration to perform their functions efficiently.
The water that leaves the body as urine, sweat, or exhaled air is ultimately extracted from blood plasma. When the blood gets more concentrated, osmoreceptors in the hypothalamus in the brain, which monitors the osmolality of the blood, trigger the thirst response, resulting in a conscious awareness of thirst. The brain also has a novel way to prevent you from drinking too much water, by reducing the swallowing reflex once you have had enough water.
Main functions of water in the body:
Water is essential for life and serves a number of essential functions to help us survive.
The water that gets absorbed has many important functions, says the Harvard Medical School:
- “Carrying nutrients and oxygen to your cells,
- flushing bacteria from your bladder,
- aiding digestion,
- preventing constipation,
- normalizing blood pressure,
- stabilizing the heartbeat,
- cushioning joints,
- protecting organs and tissues,
- regulating body temperature, and
- maintaining electrolyte (sodium) balance.”
What happens when water goes out of balance:
Additional water intake in individuals who are adequately hydrated does not confer any benefit, while excess water intake ends up as increased urine volume.
Too little water intake, however, has various health implications due to dehydration, which refers to both the process of losing body water (for example by excessive sweating or diarrhea), and also to being in a state of dehydration.
Physical activity: Athletes may lose 6-10% of body weight in sweat loss during challenging athletic events, resulting in dehydration. Even in mild levels of dehydration, individuals engaged in rigorous physical activity may experience reduced endurance, increased fatigue, reduced motivation, increased perceived effort, and altered capability in body temperature regulation. Physical activity in hot conditions with inadequate fluid replacement is linked to hyperthermia (overheating), reduced cardio output and stroke volume, reduced blood pressure, and reduced blood flow to muscles in the body. These deficits can be reversed through rehydration. In hot conditions, it is advisable to start physical activities in a state of hydration and to drink fluids over and above the thirst threshold.
Cognitive performance: Mild to moderate dehydration can affect various aspects of cognitive function, such as alterations in concentration, alertness, short term memory, disruptions in mood and may impair performance on tasks such as arithmetic ability, perceptual discrimination (what we think we see), and psychomotor skills (movement tasks that require both cognitive and motor processes). The intake of fluids under conditions of mild dehydration would normally reverse cognitive deficits caused by dehydration.
Delirium: Dehydration is a known predisposing risk factor for delirium (a state of acute confusion), as well as delirium presenting as dementia, in the elderly and people who are very ill. Older people have reduced thirst sensation and reduced fluid intakes relative to younger people. In the elderly, water balance and fluid intake can be complicated by conditions such as incontinence, dementia, disease, renal insufficiency, restricted mobility, and side effects from drugs.
Gastrointestinal function: The majority of fluid intake is absorbed by the small intestine, with the colon absorbing some of it. The absorption rate is determined by the rate of gastric emptying (which relates to the total volume consumed) to the small intestine. A case in point is constipation, which is often caused by inadequate fluid consumption. Significant water loss can also occur through the gastrointestinal tract, for example through diarrheal diseases, which not only cause a reduction in body water, but also results in potentially lethal electrolyte imbalances, especially in children.
Heart function: Blood is thicker than water, as the saying goes, and that is the way it should be, except when the blood becomes too thick. The viscosity and volume of blood is usually tightly regulated by matching water intake and water output in the kidneys. Normal fluctuations in blood volume and blood pressure in healthy individuals are balanced by slight changes in heart rate and the narrowing of blood vessels by small muscles in their walls (vasoconstriction). Loss of water or blood results in decreases in blood volume. In the event of dehydration, the blood becomes thicker and blood vessel walls become constricted. This means the heart has to work harder, by beating faster to pump blood.
Headaches: Water deprivation and dehydration have been linked to the development of headaches in some cases and can serve as a trigger for migraines and also prolong migraines in some people. Water deprived types of headaches are suspected to result from intracranial dehydration.
Skin: The skin plays an important part in water balance by maintaining body water levels and preventing water loss to the environment. Skin contains about 30% water and dehydration affects the elasticity of skin; a condition called skin turgor. Testing for skin turgor involves grasping the skin of the lower arm or abdomen between two fingers so it is tented up. When releasing the skin after a few seconds, normal skin snaps rapidly back to its original position, while skin with turgor takes time to return to its original position.
Water intake can improve skin thickness and density, as well as improving skin hydration, although adequate skin hydration is not sufficient to prevent wrinkles or other signs of aging, as they are related to genetics as well as sun and environmental damage.
The kidneys’ function in water balance:
The kidneys play a crucial role in regulating fluid balance in the body and the filtration of waste from the blood stream.
Each kidney contains more than one million filtering units, called nephrons, which are responsible for “cleaning” the blood by removing urea, excess water, and mineral ions. Nephrons reabsorb as much water as the body needs to maintain water balance, which keeps the blood plasma at the correct concentration, to prevent water entering or leaving cells by osmosis.
Blood is transported via the renal artery to the kidneys, where it passes through capillaries to be filtered at high pressure in the nephrons. The kidneys selectively reabsorb useful material in the form of small particles such as glucose, salt ions, and water. Larger particles such as blood proteins and blood cells are too big to fit through the walls of the capillaries and remain in the blood stream. After the blood has been filtered and purified, it returns to the blood circulatory system through the renal vein.
The molecules which are not selectively reabsorbed end up in the urine. The kidneys control the amount of water in the urine, which also contains urea and ions. (Urea is produced in the liver when excess amino acids are broken down.) Urea is the main waste product removed in the urine, as it is not reabsorbed in the kidneys.
Conclusions:
Water balance refers to the daily relation between the total amount of water entering the body through the ingestion of liquids and food, and the total output of water lost from the body by way of the kidneys, bowls, lungs, and skin. Water balance is carefully regulated as part of homeostasis in the body and water balance plays a critical role in maintaining our health and well-being.
In familial matters blood may be thicker than water, but in the body, water is way more important than family loyalty, as water is essential to the life and function of every single cell in the human body.
References:
Water and healthier drinks. Published online and reviewed 6 June 2022. Centers for Disease Control and Prevention. USA. (www.cdc.gov)
How much water should you drink? Published 22 May 2023. Harvard Heath Publishing. Harvard Medical School. (www.health.harvard.edu)
The water in you: Water and the human body. Published 22 May 2019. Water Science School. U.S. Geological Survey. U.S. Department of the Interior. (www.usgs.gov)
Water, hydration, and health. Published August 2010 in the journal Nutrition Review. PubMed Central. National Centre for Biotechnology Information. US National Library for Medicine. National Institutes of Health. USA. (www.ncbi.nlm.nih.gov)
Water balance. Published online. Anatomy and Physiology. Lumen Learning. (www.lumenlearning.com)
Where does water go when you drink it? Published online. Aquasana. (www.aguasana.com)
Why do we need to maintain a constant internal environment? Published online. BBC Bitesize Guide. (www.bbc.co.uk)
HEALTH INSIGHT.
March 2024