Published July 22, 2023 by

Dehydration and Blood Pressure: Can dehydration cause high blood pressure or low blood pressure?

When the body doesn't have enough fluids, dehydration occurs. Not drinking adequate amount of fluid each day or losing water faster than it can be replaced can result in this condition. 

Chronic lack of hydration is serious. If left untreated, it can lead to complications like kidney problems. Furthermore, it can cause potentially dangerous changes in blood pressure. 

Blood pressure (also called blood pressure) is the force that blood exerts on the walls of arteries and veins. Thus, dehydration can affect blood pressure, causing it to rise or fall.

Dehydration and low blood pressure 

Low blood pressure is when your blood pressure reading is less than 90/60 mm Hg (the famous 9 over 6). Due to a reduction in blood volume, dehydration can lower blood pressure. Therefore, it is necessary to maintain a normal blood volume so that it can properly reach all tissues in the body. 

However, when you are dehydrated, your blood volume can decrease, leading to a drop in blood pressure. When the pressure drops too low, the organs don't get the oxygen and nutrients they need. In this way, the body can go into shock.

Dehydration and high blood pressure 

High blood pressure is when you have a systolic reading (top number) of 140 mm Hg or higher, or a diastolic reading (bottom number) of 90 mm Hg or higher (known as 14 over 9). However, as much as dehydration has been linked to high blood pressure, research on this topic is limited. Therefore, additional studies are needed to investigate the connection. 

But, it is still worth noting that dehydration can lead to an increase in blood pressure due to the action of a hormone called vasopressin. Vasopressin levels that are too high can potentially narrow blood arteries. This can lead to an increase in blood pressure.

Symptoms of dehydration 

• Thirst; 

• Dry mouth; 

• Urinating less often; 

• Dark colored urine; 

• Tiredness; 

• Dizziness.

How much water should we drink per day? 

According to nutritionist Maria Fernanda, each person needs a different amount of water. "The variation occurs due to the weight of each individual". But, to calculate the most indicated value per day, in the case of a healthy adult. The calculation is simple: there are 35 ml of liquid per kilogram of weight. So, while a 45 kg person needs to drink 1.5 liters of water every day, someone who weighs 60 kg should drink 2.1 liters. 

However, this is the basic rule. “There are many factors that can influence and change this value. For example, elderly people and athletes need to consume more water, women who are breastfeeding and people with a faster metabolism too”, explains Maria Fernanda. In addition, external factors, such as periods of extreme heat and low relative humidity, may require more intense hydration.