Water and Hydration

Water: The Essential Nutrient

Importance of Water

  • Water is the most essential nutrient, even though it doesn't provide energy.
  • It's a macronutrient because the body needs it in large amounts.
  • Water does not contain carbon or yield energy.
  • Roughly 55-60% of the average human body weight is water.
  • Two-thirds of body water is intracellular (inside cells).
    • Muscle tissue is approximately 70% water.
  • One-third of body water is extracellular (outside cells).
    • Most extracellular water is in interstitial fluid (space between cells) and blood plasma.

Factors Affecting Water Content

  • Protein content:
    • Muscles (high in protein) contain more water than adipose tissue (fat).
    • When cells lose water, protein production slows, and protein breakdown occurs.
    • Proteins need at least a water molecule to become biologically active.
    • Water helps activate protein.
  • Carbohydrate content:
    • Glycogen is stored inside cells with water.
    • For every gram of glycogen stored, three grams of water are also stored.
    • 1 gram glycogen:3 grams water1 \text{ gram glycogen} : 3 \text{ grams water}
    • Water is needed for the complete breakdown of a glucose molecule into water and carbon dioxide.
  • Electrolyte concentration (sodium, potassium, chloride):
    • Altering electrolyte concentrations inside or outside cells influences water movement.
  • Large fluctuations in body water can lead to health concerns and poor physical performance.

Functions of Water in the Body

  • Structural integrity of cells.
  • Delivery and waste removal medium:
    • Blood and plasma distribute nutrients, hormones, immune cells, and oxygen.
    • Blood carries away waste substances like carbon dioxide, lactic acid, and ammonia.
    • Water helps the liver and kidneys function properly.
    • Low water levels cause kidneys to retain water.
  • Reactive medium:
    • Water is a reactant or product in many chemical reactions.
    • One end product of breaking down nutrients is water (metabolic water).
  • Solvent:
    • Water dissolves solutes like sodium, potassium, and chloride.
    • It is essential for molecules like glucose, vitamins, minerals, proteins, and enzymes.
  • Temperature regulation:
    • Water conducts heat 26 times faster than air.
    • Moves heat from the body's core to the periphery/skin.
    • Sweat (produced by eccrine sweat glands) cools the body upon evaporation.
    • Dehydration impairs sweat production and cooling.
  • Maintenance of blood volume:
    • Cushions brain, heart, lungs, and digestive system.
    • Maintains electrolyte balance.
    • Adequate blood volume affects blood pressure and cardiovascular function.
  • Moistens tissues in the mouth, nose, and eyes.
  • Lubricates joints:
    • Cartilage holds water to cushion movement.
    • Dehydration may cause achy joints.
  • Survival:
    • You can live for weeks without food but only days without water.

Thirst Mechanism

  • Water makes up about 70% of body weight.
  • The hypothalamus is the brain's primary thirst center.
    • It regulates body temperature, sleep, and appetite.
    • Special sensors monitor blood's sodium concentration.
    • Receives input from blood vessels monitoring blood volume and pressure.
  • Hypothalamus sends a "drink" message when:
    • Blood volume or pressure is too low (bleeding, excessive sweat, diarrhea).
    • Blood sodium concentration is too high (salty snacks, certain diseases).
  • Vasopressin (antidiuretic hormone):
    • Synthesized by the hypothalamus when the body is low on water.
    • Causes kidneys to reabsorb water from urine, reducing urine flow.
    • Conserves water in the body until more fluids are consumed.
    • A classic sign of dehydration is decreased urine volume or frequency.

Sources of Water

  • Approximately 80% of daily water needs come from fluids.
    • Broth-based soups, milk, and juices.
  • Less than 20% comes from water in fruits, vegetables, and other foods.
    • Vegetables with high water content: lettuce, cucumber, tomatoes, sugars, snap peas, and celery.
    • Fruits with high water content: oranges, pineapples, strawberries.
    • Whole fruits/vegetables are preferable to juices (more fiber).
  • Metabolic water:
    • Formed by normal cellular metabolism.
    • Carbohydrates, fats, and proteins are broken down through metabolic processes to form energy and also form water.
  • Bottled vs. tap water:
    • Water is water no matter where it comes from.
    • Tap water contains minerals from the ground.
    • Bottled water is usually filtered, with minerals and/or flavoring added.

Water Loss

  • Urination.
  • Defecation.
  • Sweating.
  • Insensible perspiration.
  • At rest, 60% of water loss is through urine formation.
  • During exercise in warm environments, sweat can account for up to 90% of water loss.
  • Insensible perspiration:
    • Water seeps through the skin and evaporates slowly.
    • Includes water loss during breathing.
    • The greater the volume of air breathed, the greater the water loss. This can be significant during exercise, at high altitudes, and in cold climates (cold air is very dry).
    • Accounts for about 15% of daily water loss.

Dehydration

  • Being slightly hyperhydrated is preferable to being slightly dehydrated for sports performance.
  • Consequences of dehydration:
    • Loss of blood volume.
    • Decreased blood flow to muscles (less oxygen delivery).
    • Increased reliance on anaerobic energy production.
    • Quicker lactic acid buildup.
    • Higher rating of perceived exertion.
    • Faster fatigue.
    • Extra heat and cardiovascular stress during exercise.
  • Cardiac drift:
    • Progressive increase in heart rate without increased exercise intensity.
    • Caused by decreasing blood volume, requiring the heart to pump faster.
  • Sweating mechanism and dehydration:
    • Water moves from high to low concentration.
    • Eccrine sweat glands pool intracellular water to form sweat.
    • Sweating decreases intracellular water content.
    • Water moves from interstitial space to intracellular space.
    • Water moves from blood plasma to interstitial space.
    • This process requires replenishment of blood plasma water via fluid consumption.
    • If fluids are not consumed:
      • Blood plasma water content decreases.
      • Sweating diminishes or stops.
      • The body is at risk for overheating, which can lead to heat cramps, heat exhaustion, and heat stroke.
  • Dehydration affecting blood volume and Heart Rate:
    • When there's a decrease in blood volume, the heart has to compensate by this by increasing its beats per minute.
    • The heart has a certain number of beats per minute that it can maximally contract at, this is called the maximum heart rate.
    • The heart can only work so hard before it can't contract any faster.

Overhydration (Hyponatremia)

  • Large influx of water is called as hyponatremia or commonly referred to as water intoxication, which occurs from hyperhydration.
  • Hyponatremia is a condition in which the fluids of the body become very low in sodium content because you have a lot or you have a huge influx of water.
  • It is possible to overhydrate the body.
  • Consume water with sodium to prevent hyponatremia, since hyponatremia can be a very serious condition that can lead to death.

Fluid Consumption Recommendations

  • The repeated rule is that you should drink at least eight glasses of water per day, however, many factors influence how much fluid you really need.
  • Eight cups of water per day isn't a bad place to start, but you will need more fluids if you work outdoors in the heat, if you're exercising frequently, if you are pregnant or nursing a baby, or if you're recovering from an illness.
  • In addition to the eight cups of water a day, which is just a guideline or recommendation, you could also take a look at your urine to look for color, volume, and frequency.
  • Research is starting to show now that drinking ahead of your thirst thirst, which would be this eight cups a day roll, may not be necessary that individuals can actually stay hydrated by at living on drinking, which means just drinking whenever you're thirsty.
  • Whenever you feel thirsty, if you drink, research is starting to show that this is also a proper way to stay hydrated and that you don't have to drink a set number of glasses per day as long as you are drinking when you're thirsty, which is called at libidom drinking.

Monitoring Hydration Status

  • Methods include monitoring body weight and urine color, specific gravity, and volume.
  • Daily weight fluctuations are primarily due to changes in water status.
  • Urine analysis:
    • Color:
      • Dark, concentrated urine with a strong smell indicates dehydration.
      • Color and smell change depending on the number of solutes.
      • Dark urine with a strong smell indicates that more solutes, which are particles, were excreted in the urine than water because kidneys are prohibiting the excretion of water due to low bodily water content.
    • Specific gravity:
      • Measures the concentration of solutes in urine.
      • Adults generally have a specific gravity in the range of 1 to 1.03.
      • Increase in specific gravity is associated with dehydration.
    • Volume:
      • Low urine volume is associated with dehydration.
      • In a dehydrated state, the kidneys do everything they can to reabsorb as much water as possible back into circulation in order to maintain blood pressure.