Water Hydration Facts and Overview
Water balance in the human body is dependent on the difference between water intake and water loss.
Constant body water content is necessary for ideal physiological functioning and maintaining optimal health.
Sources of water intake are consumption of liquids and food (~85%) and production of metabolic water (~15%).
Water loss occurs through respiration, gastrointestinal and normal kidney functioning; however, sweat losses account for the primary source of water loss.
The normal body water turnover rate in humans ranges from 1-3 liters per day (1). Hydration is a term used to describe the fluid and electrolyte concentration in the human body and is assessed by measuring the ion concentration in the bloodstream. Adequate hydration is essential because water comprises about 60% of body weight in humans and is vital to all physiologic and living processes.
Roles of Water in the Body: Cellular Health
Body water balance is primarily controlled by the brain and kidneys, which adjust urine production according to body fluid volume. As blood volume decreases (not enough water), the solute concentration (too much material in the blood) in the blood increases. This causes the release of antidiuretic hormone from the pituitary gland, which stimulates the kidneys to increase re-absorption and reduce the release of water.
This prompts the body to hold onto its current water reserves. A secondary mechanism that helps to counteract dehydration is the rennin-angiotensin system. Blood volume and accompanying blood pressure changes stimulate the production of rennin which is an enzyme that plays an significant role in hydration. This enzyme activates angiotensinogen ( a hormone) in turn to activate yet another hormone (angiotensin), which results in constriction of blood vessels and a subsequent increase in blood pressure.
When the blood vessels are constricted and blood pressures rises as a result of these natural protective mechanisms inherent in the human body, dehydration is circumvented to a certain degree and the body is able to hold onto its precious water reserves.
Water is the primary component of interstitial fluids (fluids that surround the cell). Cells are surrounded by fluids that serve a dual function and carry nutrients to the cell and carry metabolic waste away from the cell. Adequate water intake is vital for optimal cellular health.
Function of Cell Fluids
The functions of intracellular fluids (fluids inside the cell) are to assist the cell with chemical reactions and the maintenance of cell structure.
Intracellular fluids have a high potassium and phosphate ion concentration, while fluids outside the cell have a high sodium and chloride ion concentration.
These ions maintain an ideal fluid balance within and outside the cells. Water molecules follow the solutes moving across cell membranes from a lower to higher solute concentration to maintain homeostasis. Overall, water functions as a catalyst for most enzymatic reactions in the body including digestion, absorption, transport, and the metabolism of nutritional components. This includes whole food supplements, liquid vitamins and phytonutrients rich foods.
Water Benefits Help Maintain Healthy Joints and Cartilage
Water also functions to maintain joint health. Cartilage is a connective tissue that covers the ends of long bones.
Cartilage is comprised of 65-80% water and serves to maintain normal joint function. Inadequate joint hydration can cause cartilage to become brittle and limit regeneration, thereby leading to inflammation, and ultimate tissue damage if left untreated by proper hydration.
Although joint hydration partially depends on body water balance, other factors such as glycoprotien concentration, collagen network organization, and strength and stiffness of the collagen network impact joint hydration and function.
Facts on Dehydration and Key Benefits of Water
Humans are advised to consume a daily water intake of 8-12 glasses of total water, i.e. from drink and food, per day. Approximately 80% of total water intake comes from drinking liquids and the remaining 20% from eating foods.
How much water each human needs to drink can vary tremendously depending on gender, body size, physical activity level and heat exposure. When the volume of water loss is greater than the volume of water intake, dehydration occurs.
Dehydration may be caused by restricted water intake, excessive water losses, or a combination of both factors. Mild dehydration is typically defined as loss of 2-5% of body weight due to water losses. Mild dehydration produces predictable effects in humans including weight loss, thirst, mouth dryness, and swallowing difficulty.
As dehydration becomes more severe, body tissues begin to shrink, the skin dries and wrinkles and fever may develop. Blood plasma volume and stroke volume decrease, which results in decreased blood flow to the skin.
The heart rate will increase in an effort to maintain an adequate cardiac output. Sweating will decrease or stop altogether, which limits the body’s ability to effectively dissipate heat. Consequently, body temperature will rise exponentially to dangerous levels. Urine production decreases, which hinders the body’s ability to excrete waste and causes toxic levels in the bloodstream to increase.
These symptoms typically occur with moderate dehydration, defined as loss of 5-10% of body weight from water losses.
Severe Dehydration Risks
Severe dehydration (loss of > 10% of body weight from water losses) is characterized by extremely high body temperature, low cardiac output, and kidney failure. Risk for irreversible brain damage and shock increase due to these effects; these complications will ultimately lead to death if not quickly reversed.
Dehydration that results in 15% loss in body weight typically causes death from irreversible brain damage caused by high body temperature, cardiac arrhythmia (abnormal heart beat patterns) caused by low blood volume, or kidney failure with accompanying increases of toxins in the bloodstream. So we can see a foundation for health has much to do with balanced water in our body.
How Long Can We Survive Without Water?
For obvious reasons, humans can survive for only short periods without water intake, depending on several factors including temperature and activity level. In general, humans can survive for no more than 5 days without water in hot temperatures, i.e. > 100 degrees. In cooler temperatures, survival may be extended up to a maximum of 10 days assuming little to no physical activity.
Dehydration is treated by immediate replacement of lost fluids. Mild to moderate dehydration is best treated by simply drinking fluids in order to help restore a natural fluid balance.
Intravenous fluids may be administered for severe dehydration. A general rule is to replace 50% of the water loss in the first 12 hours. For example, in a patient that has lost 10 liters of fluid, the replacement rate would be over 400 ml per hour for 12 hours. Once this initial deficit is corrected, replacement of the remaining fluid needs should be more gradual to minimize the risk of heart failure.
Measurement of Hydration Status
Hydration status can be measured using several techniques, each with distinct advantages and disadvantages. These methods include total body water with dilution, measurement of plasma osmolality and volume, urine concentration, bioelectrical impedance, and body mass measurement (4).
Unfortunately, no consensus exists on the most reliable and accurate method of hydration assessment. Current recommendations are to use total body water and plasma osmolality in combination as the “gold standard” hydration measurement.
(The two pictures provide a very quick test. Pinch the skin on back of your hand and if when released your skin is raised you may be dehydrated.)
Briefly, measurement of total body water uses a known volume and concentration of an isotope that is consumed. The concentration of the isotope is later determined in a sample of body fluid after the tracer is equally distributed in the body fluids.
The unknown volume is then calculated; a low concentration of the isotope in the sample implies a large body fluid volume and vice-versa. The second method used to determine hydration status, plasma osmolality, is the measurement of the concentration of ions in circulation. Plasma osmolality is tightly controlled around a level of 285 mOsm/kg (2). Changes of 5 mOsm/kg are deemed clinically-significant; increases imply dehydration and decreases imply water intoxication.
Conclusion: Why We Need to Drink Recommended Water Daily
Water balance in the body impacts every physiological function in the body. Adequate hydration maintains proper function of the kidneys, colon, brain, cardiac system, blood vessels, and joints, and ensures adequate nutrient availability for all cells in the body.
Overall, stable water balance and adequate hydration are vital for humans to maintain homeostasis and optimal body function. Therefore, drink your recommended water daily to ensure good health. Make sure you have water available and get a table top filter for your home and a water cooler for your office from Aramark.