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This is What Happens to Your Body When You are Dehydrated

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This is What Happens to Your Body When You are Dehydrated

Water is essential for living and does more than quench your thirst. It keeps nearly all of your body's major systems functioning. The human body is made up of approximately 55-65% water.

Dehydration occurs when there is insufficient water in the body or you lose significant amounts of water quickly. Most of the time, dehydration is mild, but when severe dehydration occurs, it can be life-threatening. There are no statistics on the prevalence of dehydration in the general population, but severe dehydration more commonly occurs in the youngest and oldest populations.


What Does Water Do for Your Body?

The body has a complex system to help maintain adequate fluid balance called euvolemia. Water is required for every organ system in the body. It helps with temperature regulation, carries nutrients and oxygen to cells, lubricates joints, and moistens tissues in the eyes, nose, mouth, and entire gastrointestinal tract. It aids digestion and helps your liver and kidneys flush out toxins from your body.

Dehydration Signs & Symptoms

Common signs and symptoms of dehydration may include:

  • Thirst
  • Fatigue, tiredness
  • Dry mouth
  • Dry skin and lips
  • Decreased urine production or dark urine
  • Headaches, confusion
  • Fast or racing heartbeat
  • Low blood pressure
  • Muscle cramps
  • Lightheadedness or dizziness, particularly when changing positions or getting up quickly
  • Loss of appetite but craving sugar

How Dehydration Affects Your Brain

Water accounts for around 75% of brain mass and is needed to produce hormones and neurotransmitters and helps with focus and concentration. Severe dehydration shrinks the blood vessels, affecting memory and coordination. This can show up as symptoms of cognitive deficits such as short-term memory and visual perceptual abilities, as well as mood disturbance. Studies state that you only need to be 1% dehydrated to experience a decrease in cognitive function.

How Dehydration Affects Your Mental Health

Your mental health can also be affected by dehydration. Common mental-emotional symptoms associated with dehydration include:

  • Depression
  • Afternoon fatigue
  • Sleep issues
  • Inability to focus
  • Brain Fog

How Dehydration Affects Your Cardiovascular System

Your heart is constantly working, pumping about 2,000 gallons of blood daily. When you are dehydrated, the amount of blood circulating through your body decreases. This makes your heart work harder to compensate, increasing your heart rate and raising blood pressure.

In severe dehydration, the sensation of thirst may actually decrease, and blood pressure can fall, causing lightheadedness or fainting, particularly upon standing (a condition called orthostatic hypotension).

Keeping your body hydrated helps your heart pump blood more efficiently and allows oxygen to reach your muscles, which helps your body work more efficiently.

How Dehydration Affects Your Digestive System

Our digestive tract uses a lot of water for cleansing, lubrication, and absorption of nutrients. After consuming food, the small intestine absorbs approximately 90% of ingested water, leaving the large intestine to absorb any remaining water. The large intestine is responsible for the leftover absorption of electrolytes, vitamins, and water from waste substances and then forms and eliminates feces' from leftover waste.

When the body is dehydrated, the large intestine (colon) will soak up whatever fluids it can from the food you consume to help rehydrate the body, making feces too hard to pass and causing constipation.

Dehydration Possible Causes

There are many possible causes of dehydration. The elderly and young (children/infants) are at the highest risk.  

  • Not getting enough water in the diet
  • Vomiting or diarrhea
  • Strenuous exercise
  • Extreme temperatures - both hot and cold weather
  • Illness and infections
  • Excessive sweating
  • Increased urination, which can be caused by pharmaceutical medications like diuretics, or conditions like undiagnosed diabetes

Dehydration Risk Factors

  • Infants and young children lose a relatively higher proportion of body water with vomiting and diarrhea. Often they're unable to tell you if they are thirsty and can't get a drink for themselves.
  • Older adults - as you age, the sense of thirst decreases, and the body's fluid reserve becomes smaller. Older adults are also more likely to have chronic diseases that further increase the risk of dehydration.
  • People with chronic illnesses, such as uncontrolled diabetes or kidney disease
  • Working outside when it's hot and humid. This also increases the risk of developing heat stroke.

What Are The Levels of Dehydration?

There are three levels of dehydration.

  • Mild: most commonly occurs due to sweating too much or acute illness. This is easily reversible and usually presents with mild symptoms, like thirst, dry skin, and headache. Drinking extra fluids with electrolytes is usually all required to regain euvolemia.
  • Moderate: more symptoms like lightheadedness, usually caused by more prolonged illness, such as vomiting and diarrhea for days, and requires IV (intravenous) fluids to be given. This is done in urgent care, emergency room, or hospital setting.
  • Severe: is potentially life-threatening and requires medical attention. More severe symptoms are usually present, such as confusion, seizures, low blood pressure, and decreased urine production.

Complications from Dehydration

While rare, there are potentially severe complications from dehydration.  

  • Heat Injury and Heat stroke can occur particularly in hot and humid conditions when the body cannot cool itself adequately due to the humidity and the body overheats.
  • Urinary and kidney problems - can lead to urinary tract infections, kidney stones, or kidney failure.
  • Seizures - from severe electrolyte imbalance, particularly with very low sodium and potassium levels.
  • Low blood volume shock (hypovolemic shock) - can occur in instances where the dehydration is so severe that there's not enough blood to circulate throughout the body and maintain normal blood pressure.

Diagnosing Dehydration

There are no gold standard labs for diagnosing dehydration, but several labs can be used to help determine the degree of dehydration and its cause.

  • Urine tests - like a urinalysis, help detect electrolyte imbalances in the urine, as well as the possibility of urinary tract infection.
  • Metabolic panels that assess kidney function and electrolyte levels help determine the presence of alterations in sodium and potassium levels. BUN: Creatinine ratio should be higher than 10:1 in dehydration.
  • Ultrasound can assess the inferior vena cava (IVC) for collapsibility in severe cases.

How is Dehydration Treated?

Treatment of dehydration varies depending on the severity of dehydration. Mild dehydration is easily fixed by increasing electrolyte fluids at home. These can be purchased at the health food store. In contrast, moderate and severe dehydration often requires medical attention and IV fluids to replace lost fluid.  

How Long Does It Take For The Symptoms To Stop After Water Is Ingested?

If you are experiencing mild dehydration, you should start to feel better 5-10 minutes after drinking water with electrolytes. More severe levels of dehydration may require IV (intravenous) hydration and take a little longer to recover.

How to Prevent Dehydration?

Dehydration prevention is key to decreasing the chance of developing dehydration. Once you are experiencing thirst, you are most likely already dehydrated. If you know you will be outside in extreme temperatures, drink additional water. Make sure to drink more fluids at the onset of illness or with vomiting and diarrhea. The goal is to drink enough water to ensure your urine is pale yellow.

It is commonly suggested that a person drink daily about half an ounce to an ounce of water for each pound they weigh.

For example, if you weigh 150 pounds, you should consume approximately 75 to 150 ounces of water daily.

If you're living in a hot climate or exercise daily, you should try to consume closer to an ounce of water per pound. Adding electrolytes can help increase fluid retention in the body. Electrolytes work by directing water (and nutrients) to the areas of the body where it's needed most and help maintain optimal fluid balance inside the cells.

What are Electrolytes?

Electrolytes are essential minerals obtained from the diet and are vital to many critical functions in the body. Electrolytes have natural positive or negative electrical charges when dissolved in water. They assist the body in regulating chemical reactions and maintain the balance between fluids inside and outside of cells.

The minerals that are classified as electrolytes include:

  • Calcium
  • Chloride
  • Magnesium
  • Phosphate
  • Potassium
  • Sodium


Dehydration is a common occurrence and is most often mild, but life-threatening consequences can occur in the presence of severe dehydration. Increasing fluids and adding electrolytes when needed can lessen the chance of developing dehydration in high-risk situations. Young children and the elderly are at a higher risk of developing dehydration than other age groups and should be proactive in preventing dehydration with illness and being in extreme weather conditions.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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