How Dehydration Can Impact Your Blood Pressure

Keep that water bottle close. Drinking fluids throughout the day quenches your thirst, of course, but it also helps many critical systems in the body operate smoothly, including maintaining your blood pressure levels.

“Water is the building block of the human body,” says Kumar Sarkar, M.D., an assistant professor of cardiology at the Donald and Barbara Zucker School of Medicine at Hofstra/Northwell in Hempstead, NY. “[Water] is vital for all bodily functions, including temperature regulation, digestion, joint lubrication, and maintenance of adequate fluid level in blood vessels [that support] optimal heart function.”

That’s why treating dehydration symptoms is so important, says Blair Suter, M.D., a cardiologist at the Ohio State University Wexner Medical Center in Columbus. If you have concerns about blood pressure, dehydration, or both, here’s what you need to know.

In simplest terms, you need fluids to maintain your blood volume. When you don’t have enough fluids in your body, your blood volume decreases, and your blood pressure levels will begin to drop, Dr. Suter says. If you have high blood pressure or borderline high blood pressure, you might think this is a good thing—but it’s different than lowering your blood pressure by, say, eating less salt, and it can lead to negative health consequences.

Low blood volume results in blood vessels collapsing and reduced perfusion pressure, the pressure required to push blood through the vessels in a particular area. When this type of pressure is too low, blood can’t properly flow through those impaired vessels to the rest of the body. As a result, your overall blood pressure decreases, which can cause you to feel dizzy, confused, and lightheaded, Dr. Suter says.

It’s quite rare to experience a spike in blood pressure when you’re in a dehydrated state, Dr. Suter explains. “It’s more likely you’ll have low blood pressure when you’re dehydrated, especially when it happens quickly from illness [such as having] fever or diarrhea,” he says. However, “some patients who are dehydrated for long periods of time can [develop] high blood pressure due to high sodium levels [in the body] or kidney issues.”

Prolonged dehydration can increase the overall salt content in the body, which could lead to chronically elevated high blood pressure (also known as hypertension), according to Dr. Sarkar. Yet your body isn’t likely to let your dehydration go on for this long, Dr. Sarkar says. He explains sensory neurons in your kidneys and brain will help alert you to drink more water. If those neurons are impaired, as is sometimes the case for people with kidney disease, for instance, you may be at higher risk of dehydration, he adds.

A bout of sickness, including stomach bug or the flu, can put you at risk of dehydration, due to vomiting, diarrhea, or having a fever and losing water through sweat, Dr. Sarkar says. He also points out that exposure to hot temperatures can escalate dehydration, whether or not you’re exercising in the heat.

Taking laxatives, drinking coffee or alcohol or taking certain medications that act as a diuretic can also have a dehydrating effect, which you’ll want to counteract by upping your fluid intake. Be sure to speak with your doctor about the types of meds you’re on, so you know how much water you should aim to drink each day. For instance, diuretics like furosemide can cause dehydration and low blood pressure.

Keep a lookout for these symptoms when you suspect you or someone you know is dehydrated, Dr. Sarkar says. These include:

• Extreme thirst

• Fatigue

• Lightheadedness

• Confusion

• Decreased urine

• Very dark yellow urine

“Older adults, especially those with comorbidities such as dementia, diabetes and chronic kidney disease, may not recognize thirst or be able to notice symptoms,” he says. You’ll want to call for help if you think someone may be vulnerable to inadequate hydration.

If you’re experiencing extreme symptoms of dehydration, you must seek emergency medical attention right away, Dr. Sarkar suggests. Signs include:

• Not urinating at all, or very dark yellow or amber-colored urine

• Dry, shriveled skin

• Irritability or confusion

• Rapid heartbeat

• Rapid breathing

• Sunken eyes

• Low blood pressure

• Unconsciousness

You can prevent this extreme level of dehydration from occurring by being mindful of your water intake.

Drinking plenty of water each day is critical for overall health. And while the short-term effects of dehydration aren’t necessarily life-threatening, being dehydrated for long stretches of time can lead to irreparable consequences.

Dr. Sarkar explains short-term effects of dehydration may include reduced athletic performance, changes in mood, and temporary impairment in cognitive function. He suggests the longer you go without proper water intake, the more detrimental. “Long-term effects of dehydration may include chronic organ damage, including diseases of the heart, blood vessels, and the kidneys,” he says.

The guidelines for how much water you should drink will vary from person to person. As a benchmark, refer to the recommendations posted by the Centers for Disease Control and Prevention (CDC). In the in-house study, the organization cites guidelines created by the Institute of Medicine (IOM):

• Women should drink 2.7 liters daily (about 11.5 8-oz. glasses)

• Men should drink 3.7 liters of water daily (about 15.5 8-oz. glasses)

However, if you’re eating a diet that includes a range of fruits and veggies, about 20% of your water intake comes from food sources. So, by this metric, you may feel good after drinking just 8-12, 8-ounce glasses of water daily, for women and men respectively.

If you’re physically active your water needs will increase quite dramatically, particularly before, during and after workouts, according to The University of Michigan. Aim to drink:

• 17-20 oz. 2 hours prior to exercise

• 7-10 oz. every 10-20 minutes of exercise

• 16-24 oz. for each pound lost due to sweating after exercise

To know how much water weight you lose during exercise, you’d have to weigh yourself before and after your workout. If you’re a pound down, for instance, replenish with two or three 8-oz. glasses of water. Of course, these are just recommendations—you don’t need to step on a scale before and after every workout. Listen to your body for hydration cues, if you still feel thirsty, that’s a good indication you need to drink more water.

Check in with your health care provider to ensure you’re meeting your needs.

If you find that drinking plain water is leaving you short of your daily goal, get creative to meet your quota. Level up your H20 with citrus slices (lemons, limes, or oranges), frozen berries, herbs like mint, or cucumber slices. You could also drop an electrolyte tablet into your glass for added hydration benefits along with flavor. Or, consider reaching for hydrating foods such as watermelon, cucumber, and melon—all count as healthy and tasty ways to bump up your water intake while keeping your blood pressure in the safe zone.