04-06-2021 / Health and Fitness

Dehydration and Blood Pressure: Effects of Dehydration on Blood Pressure

Dehydration can lead to change in Blood pressure. Read more to know the connection between dehydration and blood pressure, how does dehydration affects blood pressure.

Dehydration and Blood Pressure: Effects of Dehydration on Blood Pressure
Mazia AhmedMazia Ahmed
Mazia Ahmed
MSc Nutrition Science, Ph.D. Scholar
Medically Cited
Fact Checked

Table of Content


Dehydration can be serious and cause life-threatening complications like kidney problems, heart-related emergencies and blood pressure changes if left untreated.

The most common reason for dehydration includes insufficient oral intake of water.

The other causes of dehydration include fluid loss resulting due to following:

  • Fever

  • Burns

  • Vomiting

  • Diarrhoea

  • Diabetes insipidus, diabetes ketoacidosis, glucosuria and diuretic therapy.

What is Dehydration? 

Dehydration is a condition in which there is a loss of fluid from the body. Those who do not drink enough water are at risk of dehydration. It is always important to drink enough water every day. People who have diarrhea or vomiting, frequent urination, too much sweating, exercising in outdoors during hot weather are at higher risk of experiencing dehydration.

Causes of Dehydration

Causes Of Dehydration

There are several other possible dehydration causes other than not drinking enough fluids. The following causes include-

  • Illness: Vomiting and diarrhoea can lead to a significant loss of fluid and electrolytes and a high fever, causing dehydration.

  • Increased sweating: Water is lost when sweating. An increase in sweating occurs in hot weather or during exercises, or fever, thus leading to dehydration.

  • Frequent urination: You can also lose fluid through urination while taking medications like diuretics or due to other conditions such as alcohol consumption or diabetes that cause frequent urination resulting in dehydration.

  • Diarrhoea: In diarrhoea, the patient may pass loose stools three or more times a day which causes dehydration. The body's normal functioning is affected as it does not have enough fluid to function. The first step in the treatment of diarrhoea is to correct dehydration. Oral Rehydration solution (ORS) is given to replace the lost fluid and maintain the electrolyte balance. The patient is instructed to drink enough water.

  • Vomiting: The signs of dehydration due to vomiting manifest as dry mouth, infrequent urination and dark urine. The patient is advised to drink enough water often.

  • Fever

  • Intake of insufficient water

  • Chronic illness: There are chronic conditions like diabetes, cystic fibrosis, kidney problems, etc., in which the frequency of urination and sweating is more. This causes dehydration in such patients.

  • Medications

  • Exercising in hot weather

Symptoms of Dehydration

Symptoms Of Dehydration

It is very important for you to know the symptoms of dehydration. When you know the problem's reason, it is easy to opt for a solution. Some of the symptoms of dehydration are:

  • Dry skin

  • Dry mucus membrane

  • Reduce skin turgor

  • Orthostatic hypotension

  • Reduce axillary sweating

  • Cognitive impairment

  • Tachycardia and hypertension

  • High osmolality and concentrated urine

  • Reduced urinary output

  • Feeling fatigued or tired

  • Dizziness and lightheadedness

  • Confusion

  • Dark-colored urine

Biochemical Changes Due to Dehydration

  • Raised creatinine

  • Raised serum urea

  • Increased urea and creatinine ratio

  • Reduced estimated glomerular filtration rate

  • Hyponatremia

  • Raised urine specific gravity

  • Raised serum or urine osmolality

  • Dehydration affecting your blood pressure

How Does Dehydration Affect Blood Pressure?

1. Dehydration and Low Blood Pressure

In Dehydration, blood pressure is low, meaning less than 90/60 mm Hg. Dehydration causes low blood volume and is a life-threatening condition which may lead to shock. The body does not receive the nutrition and oxygen they need when blood pressure drops too low, potentially resulting in shock.

2. Dehydration and High Blood Pressure

High blood pressure occurs when the systolic blood pressure reading is 140 mm Hg or higher and the diastolic reading is more than 90 mm Hg. There is a link between high pressure and dehydration because dehydration can increase blood pressure due to the action of a hormone called vasopressin. This hormone is secreted when there's a higher amount of solute in the blood or low blood volume. Our kidneys absorb water, but dehydration opposes urine from passing. Moreover, when you are dehydrated, and high concentration of vasopressin can also cause your blood vessels to constrict, leading to increased blood pressure.

How Does Dehydration Affect Blood tests? 

Blood samples check several factors like electrolyte levels, namely sodium and potassium, blood glucose profile, etc., which confirm dehydration. The tests also dictate the functioning of the kidneys.

9 Effects of Dehydration on Hematocrit

1. Effect of Dehydration on Haemoglobin

If a person is severely dehydrated, the haemoglobin will appear higher than the patient with normal blood volume. Also, if the patient's fluid is overloaded, the haemoglobin range will be lower than its actual level. This is because haemoglobin and hematocrit are based on whole blood volume and depend on plasma volume.

2. Effect of dehydration on CBG measurement

Dehydration causes hypertension and increases glucose utilisation in the local tissues. Thus this leads to the false low result of the capillary blood glucose (CBG) test.

3. Effect of Dehydration on Blood Glucose

The rise in glucose is out of proportion to changes in metabolite concentrations that could be due to the plasma's passive concentration (haemoconcentration) due to dehydration. Also, an increase in hepatic glucose production, with increased plasma glucose levels during hyperosmolality, can be caused by dehydration.

4. Effect of Dehydration on Renal Function Test

Dehydration has multiple effects on the kidney. The loss of body water leads to increased serum osmolality and vasopressin activation, which results in urinary concentration.

5. Effect of Dehydration on Liver Function Test

There is a significant difference in serum total albumin and protein levels in a dehydrated patient before and after hydration with intravenous fluid. Still, the liver enzymes and bilirubin levels remain unchanged, indicating the change in protein level due to dehydration status rather than a liver abnormality.

6. Effect of Dehydration on Lipid Profile

An investigation has been carried out in fasting subjects to see dehydration on lipid profiles. The subjects were allowed to fast firstly with no fluid replacement and then with salt and water supplements, where the fasting subjects with no fluid had higher total serum cholesterol, LDL cholesterol, HDL cholesterol, apolipoprotein A1 and apolipoprotein B compared to the subject who had fasted with salt supplements and prior fluids.

7. Effect of Dehydration in Cholesterol Test

Dehydration causes blood volume to decrease, leading to a drop in blood pressure and blood flow, resulting in cholesterol accumulation in the arteries. To protect cell membranes, the body may increase the production of cholesterol in response to severe dehydration.

8. Effect of Dehydration in a Lab Blood test and Blood pressure

Due to dehydration, there can be inaccurate blood test results as suspected, as water accounts for approximately 60% of the adult human body weight. So, lack of water may lead to dehydration and thus affecting blood pressure and blood test results.

9. Effect of Dehydration in Kidney Value Test

Two of the most common tests for diagnosing kidney diseases and evaluating kidney functions are the creatinine test and the blood urea nitrogen (BUN) test. Higher volumes of BUN and creatinine indicate that the kidney is not working properly as the test measures the amount of waste product in the blood. Dehydration can reduce the blood flow to the kidney and can elevate the blood urea nitrogen level and creatinine level in the blood.

What are the other causes of high blood pressure?

It is always important to know that if you are overweight, not eating enough fruits and vegetables, taking too much salt, smoking, or experiencing disturbed sleep means “You are at risk of developing high blood pressure.” Maintaining a healthy lifestyle is the key to a healthy life.

Some of the causes of high blood pressure are:

  • Kidney diseases, infection, glomerulonephritis, etc.

  • Diabetes

  • Hormonal causes related to an underactive and overactive thyroid, Cushing syndrome, acromegaly, etc

  • Skin diseases like scleroderma and lupus.

  • Medications

When to get medical attention

When to Seek Care for Dehydration :

The symptoms of dehydration are feeling thirsty, Dryness in the mouth, less urination and sweating, passing dark-coloured urine, tiredness and dizziness. These are the mild to moderate symptoms of dehydration. However, other life-threatening symptoms of dehydration require immediate medical attention, such as confusion, fainting, Lack of urination, rapid heartbeat, and rapid breathing. These symptoms lead to shock

Shock is a life-threatening emergency in which insufficient blood and oxygen supply occurs to all the body cells, tissues and organs. As a result of dehydration, the blood pressure may drop too low and endanger the patient's life. Shock is immediately treated based on the underlying cause. 

The dehydration is confirmed by physical examination, monitoring vital signs (blood pressure, heart rate, respiratory rate and temperature.) and by the patient’s history.

When to Seek Care for Blood Pressure :

  • Chest pain (angina), fainting sensations, falling due to lightheadedness, cold, sweating, fast breathing and rapid heart rate are some of the symptoms related to low blood pressure.

  • When one experiences sudden onset severe headache, nose bleeding, chest pain, shortness of breath, and visual difficulty, these signs of hypertensive crisis require immediate medical attention.

What is the correct way to measure blood pressure?

How To Get An Accurate Blood Pressure Reading

Follow these steps to get an “accurate” blood pressure reading:

According to the CDC, one must follow these steps to get accurate blood pressure readings.

  • No eating or drinking before 30 minutes of reading.

  • No alcohol and coffee before reading.

  • Empty the bladder.

  • Sit comfortably.

  • Sit quietly

  • Your back should be supported.

  •  The feet should be flat on the ground.

  • Legs should be uncrossed.

  • The arm should rest at chest height.

  • Elbow should be at or near heart level.

  •  The blood pressure cuff should not be too tight. 

  • The cuff should be on the skin. 

  • The cuff should not be over the clothing.

  • Do not talk.

  • Always take two readings.

  • Maintain a record of reading, including the time of the day.

How much water should you drink each day?

According to Haward health, drinking water has many health benefits that everyone must know. Dehydration is best prevented by drinking water.

The benefits of drinking sufficient water are cells of the body get nutrients and oxygen, bacteria are flushed out from the bladder, digestion becomes healthy, constipation is prevented, blood pressure is normal, joints are healthy, body temperature is controlled, electrolyte levels are best maintained, and overall body is protected.

One must drink 2.5 litres of water per day. But your body may demand more water due to medical conditions like thyroid, diabetes, kidney diseases, etc.

Home Remedies for Dehydration

Home Remedies For Dehydration


  • Drink water throughout the day.

  • Eat salads

  • Eat fruits

  • Drink water before, during and after exercise. Take a sip.

  • Avoid coffee.

  • Do not skip meals.

  • Eat a balanced diet.

  • Avoid alcohol.

  • Drink more in hot weather.

  • Drink more water when you are sick.

  • Always carry your water bottle wherever you go.

  • Set timely reminders to cover daily intake of 2.5 litres of water.

Do you know how fruits and vegetables can help in maintaining hydration:

Do you know how fruits and vegetables can help in maintaining hydration

Best fruits to eat in dehydration to maintain water level:

  • Watermelons contain 90 % of water and is low in calories. This fruit can provide you with the best hydration.

  • Strawberries are a combo of water and nutrients. Strawberries have other health benefits also, like protection from heart disease and cancer.

  • Peach contains 85 % of water and other important nutrients.

  • Bananas and avocados have 70 – 79 % of water.

  • Apples, grapes, pineapple, pears and oranges have 80-89 % water content.

Best vegetables to eat in dehydration to maintain water level:

  • Lettuce, cabbage and spinach have 90-99 % water.

  • Carrots and broccoli have 80-89 % of water.

  • A baked potato has 70 % water.

  • Cooked corn has 70-79 % of water.

Some interesting facts about dehydration:

Some Interesting Facts About Dehydration

Know these interesting facts about dehydration. Many of the facts are still under research. 

  • Individuals involved in sports and athletic activities experience reduced performance and feel demotivated due to dehydration.

  • Dehydration or lack of water affects cognition. In dehydration, one may experience a lack of concentration and alertness.

  • Dehydration causes confusion.

  • When you experience constipation, ask yourself, “ I am drinking less water?”

  • Oral rehydration solutions replace fluids lost by diarrhoea.

  • Kidneys need water to filter waste products.

  • Water reduces heart rate and normalises blood pressure.

  • Drinking 300 ml of water corrects postural hypotension.

  • Dehydration causes headaches.

  • Water intake relieves headaches within 30 minutes.

  • Drinking 8-10 glasses of water make skin glowing.

  • The skin has 30 % water.

Take-Home Points

  • Everyone must monitor their blood pressure regularly. If the readings come above 180/120 mm Hg, the person should rest for 5 minutes and then recheck the reading again. If the reading comes high again, it is always important to consult the physician.

  • Certain medicines for treating high blood pressure cause dizziness so if the patient experiences this frequently, then this must be consulted with the doctor.

  • It is always important to be cautious about health. If any unusual sign is detected, it should be discussed for betterment and awareness.

  • The best sign to check dehydration is urine. When the body has plenty of water, urine is light-coloured.

FAQ on Dehydration and Blood Pressure

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