Being dehydrated can cause a whole slew of side effects, beyond just making you feel crummy. But does dehydration cause high blood pressure? Or on the flip side there is a link between drinking too much water and high blood pressure? Understanding how your body responds to dehydration can help you prevent potentially dangerous alterations in your blood pressure.

What is dehydration?

Dehydration is a health condition that occurs when your body doesn’t have enough fluids. It can result from both not consuming enough fluids from foods and beverages, as well as losing bodily fluids — through processes like excretion and sweating — at a faster rate than they’re being replaced. 

We’ve all been dehydrated at one point or another. In fact, some surveys estimate that 75% of Americans are chronically dehydrated. When it’s not addressed, dehydration can become severe and even pose life-threatening risks.1

Untreated dehydration can promote things like kidney issues, heat sickness, and dangerous changes in blood pressure.

Symptoms of dehydration

Knowing what signs to look out for can help you prevent dehydration from becoming an emergency situation. 

Some of the most common dehydration symptoms include: 

• Feeling thirsty
• Dry mouth
• Urine that’s darker in color and less frequent
• Feeling dizzy or lightheaded
• Fatigue 
• Mental fog or confusion

Signs of severe dehydration can progress to things like blurred vision, nausea, cold and clammy skin, shallow breathing, and a weak but rapid pulse. 

If you notice serious dehydration symptoms like these or are concerned about potentially low blood pressure levels, it’s always best to seek medical attention.

How does dehydration affect blood pressure?

When you become dehydrated, it’s likely that you’ll experience some of the symptoms listed above before you realize that there have also been changes in your blood pressure. 

Blood pressure is how forcefully your blood moves through your veins and arteries, and how much pressure it places on the walls of your circulatory system.2

A blood pressure of around 120/80 mm Hg is considered to be normal and healthy for most people. The top number refers to your systolic blood pressure, which indicates the pressure your blood is placing on your artery walls during heartbeats. The bottom number refers to your diastolic blood pressure, which indicates the pressure your blood is placing on your artery walls when your heart is at rest, or between beats. 

These numbers can be influenced by a variety of things, including your hydration status. When you’re dehydrated, your blood pressure can actually go either up or down.

A low blood pressure reading is typically anything below 90/60 mm Hg. When you’re dehydrated, this can lead to a reduction in total blood volume, which in turn reduces how much force your blood is exerting on your arteries. Left untreated, this becomes dangerous because having low blood volume means your organs won’t receive the nutrients and oxygen they need to survive. This could ultimately lead to shock. 

A high blood pressure reading is usually above 140/90 mm Hg. While the mechanism is less intuitive, being dehydrated can also raise blood pressure levels. It appears to be related to dehydration-induced changes in the secretion of a hormone called vasopressin. 

Vasopressin is a pituitary hormone released to increase blood pressure and promote water retention by your kidneys, instead of losing it through urine excretion. When you’re dehydrated, more vasopressin is secreted in an attempt to rebalance fluid and blood pressure levels. 

Why does this increase blood pressure? Vasopressin can make your blood vessels constrict, which consequently reduces the space through which your blood is circulating and increases its force on arterial walls.

Causes of dehydration

The most obvious reason behind becoming dehydrated is not drinking enough fluids. However, water and high blood pressure can be tricky. 

Other factors can also promote dehydration, such as: 

• Illness: Being under the weather, especially when you’re experiencing diarrhea and/or vomiting, puts you at risk of losing more fluids than you can replenish — as well as promoting electrolyte imbalance. 
• Increase urination: Certain medical conditions, like diabetes or prediabetes, as well as taking diuretic medications, can lead to urinating more frequently than usual. 
• Increased sweat loss: Having a high fever, engaging in a difficult workout, or spending a period of time in the hot sun can promote excessive fluid loss through sweating.

In all of these instances, it’s important to stay hydrated to help replenish fluids lost. Sipping small amounts of water or broth throughout the day when you’re sick, electrolyte-containing beverages during a tough workout, and hydrating foods and beverages when you’re outdoors are all good practices to remember to prevent dehydration. 

How much fluid should you drink?

Daily fluid needs vary between individuals because they depend on unique factors like how old you are, your sex, existing health conditions, any medications you’re taking, your activity level, and if you’re pregnant or breastfeeding. 

According to the Mayo Clinic and U.S. National Academies of Sciences, Engineering, and Medicine, a general rule of thumb is to aim for:3 

• About 15.5 cups (3.7 liters) of fluids a day for men
• About 11.5 cups (2.7 liters) of fluids a day for women

When you schedule a 1:1 session, I can help personalize a nutrition and hydration plan for you to meet your health goals like managing blood pressure and improve your cardiovascular function and health.

Hydrating foods and beverages

The best fluid for hydration is regular water. 

However, if you find that you’re getting sick of drinking plain water all the time, there are some ways to enhance its flavor and rotate in other hydrating beverages and foods. 

For instance: 

• Add fresh berries, lemon or lime wedges, or sliced cucumber to naturally flavor regular water
• Seltzer water with natural flavors
• Decaffeinated herbal teas
• Smoothies made with fruits and vegetables
• Low sodium soup and broths
• Popsicles
• Fresh produce, like watermelon, strawberries, salad greens, apples, citrus fruits

Beverages and blood pressure medications

Keep in mind that some hydrating beverages, particularly herbal teas, have been found to naturally lower blood pressure.4 This can be helpful to a degree, but can actually cause blood pressure to drop too much if you’re taking medications that are intended to lower blood pressure.

For instance, research has found that drinking daily hibiscus tea — even in doses of 10 grams of hibiscus per 0.5 Liters — can lower blood pressure both among people who are and are not taking medication.5,6

In one meta-analysis including 24 studies, researchers found that green tea could also significantly lower systolic and diastolic blood pressure in short-term trials. Even doses of 120 mL (a half cup) per day of green or oolong tea have had this effect when people are drinking it regularly over a long period.7

Other research has found that 3 cups of black tea per day is also effective for lowering blood pressure when people are drinking it consistently for at least 6 months.8 

This doesn’t mean you should stop drinking your favorite teas if you use blood pressure medications, but it does mean it’s important to monitor your blood pressure closely to make sure it stays within a healthy range.

Help keep your blood pressure in check by monitoring it with a blood pressure cuff or reader. Additionally, going to regular preventative health check-ups is important to catch any potential heart health and blood pressure concerns before they worsen.

Seeking support for high blood pressure

If you’re concerned about your blood pressure and how your hydration or other lifestyle habits may be affecting it, seeking professional support is a great step forward. 

As a registered dietitian who specializes in cardiac care, I’ve helped thousands of people achieve their heart health goals, including blood-pressure friendly tips to stay hydrated. In your sessions, we can create a heart healthy hydration and nutrition plan for you, so you can feel confident that you are drinking enough (but not too much!) and that you are adding in therapeutic foods that help mange your blood pressure, and optimize your heart health and function!

Let’s connect for personalized 1:1 counseling to help you manage your high blood pressure with confidence.

References

1. Taylor K, Jones EB. Adult Dehydration. [Updated 2021 Oct 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555956/
2. “Understanding Blood Pressure Readings.” American Heart Association. Available from https://www.heart.org/en/health-topics/high-blood-pressure/understanding-blood-pressure-readings 
3. “Water: How much should you drink every day?” Mayo Clinic. Published 14 Oct 2020. Available from: https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/water/art-20044256 
4. Mahdavi-Roshan M, Salari A, Ghorbani Z, Ashouri A. The effects of regular consumption of green or black tea beverage on blood pressure in those with elevated blood pressure or hypertension: A systematic review and meta-analysis. Complement Ther Med. 2020;51:102430. doi:10.1016/j.ctim.2020.102430
5. Jalalyazdi M, Ramezani J, Izadi-Moud A, Madani-Sani F, Shahlaei S, Ghiasi SS. Effect of hibiscus sabdariffa on blood pressure in patients with stage 1 hypertension. J Adv Pharm Technol Res. 2019;10(3):107-111. doi:10.4103/japtr.JAPTR_402_18
6. Al-Anbaki M, Nogueira RC, Cavin AL, et al. Treating Uncontrolled Hypertension with Hibiscus sabdariffa When Standard Treatment Is Insufficient: Pilot Intervention. J Altern Complement Med. 2019;25(12):1200-1205. doi:10.1089/acm.2019.0220
7. Xu R, Yang K, Ding J, Chen G. Effect of green tea supplementation on blood pressure: A systematic review and meta-analysis of randomized controlled trials. Medicine (Baltimore). 2020;99(6):e19047. doi:10.1097/MD.0000000000019047
8. Li D, Wang R, Huang J, et al. Effects and Mechanisms of Tea Regulating Blood Pressure: Evidences and Promises. Nutrients. 2019;11(5):1115. Published 2019 May 18. doi:10.3390/nu11051115