Can severe dehydration cause high blood pressure

— Written By John Cartwright

Updated on October 27, 2022

Dehydration can have various negative effects on your body, including dizziness and tiredness. It can also affect your blood pressure. Dehydration occurs when the amount of water in your body decreases. This can be due to reduced fluid intake or increased fluid loss, and it can lower the volume of blood in your body. As a result, dehydration can affect blood pressure.

This article looks at the symptoms of dehydration and high blood pressure and the possible effects of dehydration on blood pressure. It also discusses other potential causes and complications of high blood pressure and explains when you should contact a doctor.

Can dehydration cause high blood pressure?

Chronic dehydration can cause high blood pressure. If you become dehydrated, your body will secrete a chemical that causes your blood vessels to constrict, which then increases your blood pressure. 

In addition, dehydration can cause your blood to retain more sodium. This thickens it, making it more difficult for your heart to pump around your body.

In the short term, however, dehydration may not cause an immediate effect on blood pressure.

What are the effects of dehydration on blood pressure?

Dehydration can have different effects on blood pressure, potentially making it lower or higher than usual.

Low blood pressure

Dehydration can often cause low blood pressure for much the same reason it can cause high blood pressure.

Not having enough water causes your blood volume to drop, and a drop in blood volume means that the pressure of blood in the body reduces. 

High blood pressure

A chronic decline in blood volume can lead to higher blood pressure, as the lack of water in the body’s cells causes the pituitary gland to secrete vasopressin. This leads to the blood vessels in the body constricting, thereby increasing blood pressure.

Learn about commonly prescribed drugs for high blood pressure.

What are the symptoms of dehydration?

As well as potentially causing blood pressure changes, dehydration can produce other symptoms. These include:

• strong-smelling, dark yellow urine
• feeling tired, dizzy, or lightheaded
• dry mouth, lips, and eyes
• urinating fewer than four times a day
• reduced skin turgor

What else can cause dehydration?

Although dehydration is typically the result of not drinking enough water, there canbe other causes and contributing factors, including:

• vomiting or diarrhea
• sweating
• heatstroke
• diabetes
• diuretic medications

How much water should you drink each day?

To avoid dehydration, it is vital that you drink enough water on a daily basis.

Although various factors — such as age, weight, and physical activity — affect the amount of water you need, the general recommendation is to drink about 2.5 liters of water a day.

What else can cause high blood pressure?

As well as dehydration, a number of factors can increase your risk of hypertension. These include:

• eating a diet high in salt
• carrying excess body weight
• doing insufficient exercise
• consuming an excessive amount of alcohol or caffeine
• smoking
• getting insufficient sleep or experiencing frequent sleep disturbances

Various medical conditions can also cause high blood pressure. These include:

• kidney disease and infections
• diabetes
• obstructive sleep apnea
• lupus 
• scleroderma

What are the complications of high blood pressure?

High blood pressure can cause a range of issues throughout your body because it puts strain on your heart, blood vessels, brain, and kidneys. It can put you at higher risk of many health conditions, including:

• heart disease, heart attacks, and heart failure
• strokes
• kidney disease
• vascular dementia
• peripheral arterial disease
• aortic aneurysms

Learn more about the dangers of dehydration.

When should you see a doctor?

If you are concerned about high blood pressure, you should contact your doctor as soon as possible. In most cases, there are no clear warning signs of high blood pressure, so the only way to know whether you have it is to get a blood pressure measurement.

Blood pressure measurements are quick and painless, and it is possible to take them at home if you have a blood pressure monitor.

When testing blood pressure, the doctor will take two readings: systolic and diastolic. Systolic blood pressure is the pressure in your arteries as your heart beats, and diastolic blood pressure is the pressure in your arteries between heartbeats. 

Doctors classify blood pressure below 120 millimeters of mercury (mm Hg) systolic and 80 mm Hg diastolic as healthy. High blood pressure refers to measurements above either 140/90 mm Hg or 130/80 mm Hg. If your results show that you have high blood pressure, the doctor will likely recommend a number of lifestyle changes, including:

• engaging in at least 150 minutes of moderate intensity physical activity a week
• stopping smoking
• reducing salt and alcohol intake

The doctor may also prescribe medications to help with high blood pressure. Different medications can help lower your blood pressure in various ways, such as:

• reducing water and salt in your body
• relaxing blood vessels
• reducing the force with which your heart beats
• blocking nerve activity that could restrict blood vessels

Learn more about seeing a doctor for high blood pressure.

Summary

Chronic dehydration can cause high blood pressure. The lack of blood volume due to dehydration can cause the pituitary gland to secrete vasopressin. This, in turn, will cause the blood vessels in the body to constrict, thereby increasing blood pressure.

High blood pressure can also result from dietary factors, lack of exercise, smoking, and a range of medical conditions. It can cause various complications, such as heart conditions, kidney disease, and stroke. As it rarely produces symptoms, the only way to know whether you have it is to get a blood pressure measurement. 

If you have any concerns about high blood pressure, contact a doctor as soon as possible. The doctor can test your blood pressure and advise you on any lifestyle adjustments you should make. They can also prescribe medication to treat the condition, if necessary.