Dehydration occurs when your body loses more fluids and electrolytes than you’re taking in.
You can become dehydrated if you’re not drinking enough water or if you’re sweating, urinating, or otherwise losing more fluids than you’re consuming.
It can be very dangerous, especially if you remain dehydrated for a long period of time.
Being dehydrated can affect your body’s normal function in several ways, and cause headaches, dizziness, and create changes in blood pressure.
It can be remedied by drinking fluids or, in extreme cases, receiving intravenous fluids.
In this article I will review important aspects about dehydration and blood pressure.
Can Dehydration Affect Your Blood Pressure?
Dehydration can cause changes in your blood pressure, and it can also lead to potential health problems.
Dehydration and High Blood Pressure
High blood pressure refers to a systolic blood pressure above 130mmHg and diastolic blood pressure above 80mmHg.
Studies have shown that dehydration can cause an increase in blood pressure, and a study conducted in rats recurrent dehydration can worsen hypertension.
When you’re dehydrated, your blood has a higher concentration of sodium, and in response, the brain sends signals to the pituitary gland to secrete vasopressin.
Vasopressin, also called antidiuretic hormone (ADH), plays a crucial role in the body’s osmotic balance, blood pressure regulation, sodium regulation, and kidney functioning.
Vasopressin tells your kidneys to reabsorb more water and when released in high enough concentrations, vasopressin causes vasoconstriction, which leads to an increase in blood pressure.
If you’ve been diagnosed with hypertension, do your best to stay consistently hydrated to avoid spikes in blood pressure.
Dehydration and Low Blood Pressure
Dehydration can lead to low blood pressure by reducing your blood volume.
Low blood pressure is a systolic blood pressure reading less than 90mmHg and diastolic blood pressure less than 60mmHg.
Blood volume is the total amount of fluid moving through your circulatory system (arteries, veins, capillaries, heart chambers) at any given time.
Your blood volume depends on how much fluid you’re taking in. Therefore, when you’re dehydrated, your blood volume reduces.
A decrease in blood volume (hypovolemia) can be caused by blood loss (donation or injury) or sweating a lot during exercise in addition to not drinking enough.
Reduced blood volume causes blood pressure to reduce, leading to low blood pressure.
Low blood pressure can make you feel dizzy, weak, and tired.
Severe cases of low blood pressure can lead to shock, which needs treatment in a hospital or can even lead to death.
What Is Dehydration?
Dehydration occurs when the body loses more fluid than it gains.
Fluid loss can also often mean the loss of essential electrolytes, sugars, and salt.
As a result, there’s less water available for the body to carry out its normal functions.
Causes of Dehydration
Dehydration is caused by losing fluids faster than you replace them.
Most times, dehydration is simply the result of not drinking enough water.
Older people usually have a lower volume of water in their bodies, which increases their risk of getting dehydrated.
Here are some other reasons why you might be dehydrated:
- Diarrhea: Diarrhea can lead to serious loss of body fluids. When someone has diarrhea, their food spends a shorter time in their digestive system, and water isn’t absorbed when it gets to the large intestine. This water is excreted along with fecal matter, which leads to dehydration.
- Sweating: You lose a lot of water from sweating in hot weather or during exercise. Insufficient water intake after a long day of excessive sweating can lead to dehydration. In addition, in very cold climates, fluids can be lost without sweating due to increased respiratory losses.
- Vomiting: Like diarrhea, vomiting leads to a rapid loss of body fluids and minerals. When people are nauseous or vomiting, it may be harder to keep water down, putting them at significant risk of dehydration.
- Frequent urination: If you find yourself urinating more often, drink more water to avoid getting dehydrated. Frequent urination may be due to diuretics, some blood pressure medications, antihistamines, and antipsychotics. It can also be caused by uncontrolled diabetes.
- Fever: When you have a fever, your body tries to cool itself by sweating, which results in loss of body fluids. If you don’t drink enough water to replace what’s lost, you may become dehydrated.
Symptoms of Dehydration
If you’ve gone without water for a while and suddenly feel thirsty or notice that you don’t need to urinate as often, there’s a high chance that you’re dehydrated.
Note, however, that dehydration doesn’t always make you thirsty.
This is especially so in older adults, and also why you shouldn’t always wait until you’re thirsty before drinking that glass of water.
Here are some other symptoms of mild to moderate dehydration:
As dehydration progresses, the symptoms become more serious. With severe dehydration, you may experience:
- Lack of sweating
- Severe headache
- Excessive thirst
- Sunken eyes
- Shriveled skin
- Quickened heart rate
- Low blood pressure
- Rapid breathing
- Very dark urine
Babies can’t talk, so they won’t be able to tell you if they feel dehydrated.
These are some signs of dehydration to look out for in children:
- Dry mouth
- No tears when they cry
- Dry diapers after three or more hours
- Sunken cheeks
How Much Water Should I Drink Every Day?
You’re probably familiar with the famous advice to drink eight glasses of water a day. That isn’t quite accurate.
Research proves that men may need to drink up to 3000ml (almost 13 cups) of water and women 2200ml (9 cups of water) daily.
However, this recommendation isn’t set in stone as individual circumstances and environmental factors differ.
How much water you should drink in a day can be influenced by how physically active you are, what medications you’re taking, and the general state of your health.
If you exercise regularly and sweat during your workouts, you may need to drink more water.
You would also need to drink more water if you’re in a hot environment that causes you to sweat and lose body fluid.
If you’re ill, you can lose body fluids from vomiting, diarrhea, and fevers.
Your health care provider might recommend oral rehydration solutions in this case.
You also need to drink more water if you’re pregnant or breastfeeding.
Ultimately, don’t overthink it. Drink water when you feel thirsty — and then a bit more.
When to Seek Medical Attention
Mild dehydration can be treated at home by drinking water and other beverages containing electrolytes.
But if you notice more extreme symptoms of dehydration, seek medical attention.
When to Seek Care for Dehydration
Dehydration can lead to medical complications in severe cases.
Contact your health care provider if you (or someone under your care) experience any of the following symptoms:
- Rapid heartbeat and breathing
- Sunken eyes
- Lack of tears when crying
- Inelastic skin
- Sunken soft spot on a baby’s head
- Low blood pressure
When to Seek Care for Blood Pressure
If your blood pressure goes below 90/60mmHg and you feel any of these symptoms, seek medical attention:
- Blurred vision
- Shallow breathing
- Weak but rapid pulse
- Loss of consciousness
Seek medical attention if you’re hypertensive (blood pressures above 130/80) and develop any of these symptoms:
- Shortness of breath
- Chest pain
- Difficulty speaking
- Severe headache
How K Health Can Help
Getting medical care when you feel dehydrated can be fast and easy.
Did you know you can get affordable primary care with the K Health app?
Download K to check your symptoms, explore conditions and treatments, and if needed, text with a doctor in minutes. K Health’s AI-powered app is HIPAA compliant and based on 20 years of clinical data.
Frequently Asked Questions
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
The Effect of Acute Mild Dehydration on Blood Pressure Control (2021)
Physiology, Vasopressin (2021)
Hydration Status and Cardiovascular Function (2019)
Two Liters a Day Keep the Doctor Away? Considerations on the Pathophysiology of Suboptimal Fluid Intake in the Common Population (2017)
Chronic recurrent dehydration associated with periodic water intake exacerbates hypertension and promotes renal damage in male spontaneously hypertensive rats (2016)
Is this elderly patient dehydrated? Diagnostic accuracy of hydration assessment using physical signs, urine, and saliva markers (2015)
How much water do we really need to drink? (2011)
Water, Hydration and Health (2011)
Effect of water drinking on sympathetic nervous activity and blood pressure (2005)
Mineral water intake reduces blood pressure among subjects with low urinary magnesium and calcium levels (2004)