Is dehydration raising your blood pressure? Here's the science
From the desk of Robb Wolf
<p><span style="font-weight: 400">The more we learn about the human body, the more links we discover between hydration and </span><a href="https://drinklmnt.com/blogs/health/electrolytes-and-heart-health" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">heart health</span></a><span style="font-weight: 400">. Today you’ll learn about one of those links: the link between dehydration and blood pressure.</span></p><p><span style="font-weight: 400">When people are dehydrated, they’re low on body water. Low body water means low blood volume, which generally leads to low blood pressure. I’ll elaborate later, but that’s the Twitter-friendly version of why low blood pressure is a common </span><a href="https://drinklmnt.com/blogs/health/dehydration-causes-and-symptoms" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">dehydration symptom</span></a><span style="font-weight: 400">.</span></p><p><span style="font-weight: 400">But can dehydration cause </span><i><span style="font-weight: 400">high </span></i><span style="font-weight: 400">blood pressure? The story isn’t entirely clear, but the </span><a href="https://academic.oup.com/nutritionreviews/article/73/suppl_2/97/1930742" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">correlational data</span></a><span style="font-weight: 400"> is there. That’s right. Through different mechanisms, dehydration may cause both low AND high blood pressure.</span></p><p><span style="font-weight: 400">It’s not intuitive, but reality isn’t calibrated to align with our intuitions. If something </span><i><span style="font-weight: 400">seems </span></i><span style="font-weight: 400">intuitive, we should pause and revisit the basic assumptions upholding that intuition. Despite the vigorous head bobbing that follows any mention of </span><a href="https://en.wikipedia.org/wiki/Occam%27s_razor" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">Occam’s razor</span></a><span style="font-weight: 400">, the simplest explanation isn’t always the correct one.</span></p><p><span style="font-weight: 400">But don’t worry, I won’t overcomplicate this topic. I’ll simplify the nuance as best I can, and occasionally add a dash of humor to help keep you with me.</span></p><p><span style="font-weight: 400">Stick around for 5 minutes to learn about dehydration and low blood pressure, dehydration and high blood pressure, other causes of high blood pressure, and </span><a href="https://drinklmnt.com/blogs/health/how-to-stay-hydrated" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">how to stay properly hydrated</span></a><span style="font-weight: 400">. First things first: let’s cover some basics.</span></p><h2><b>What Is Dehydration?</b></h2><p><span style="font-weight: 400">Dehydration is a state of net water loss from the body. This water loss, in turn, results in a condition of low body water called hypohydration. (Note: dehydration and hypohydration are technically distinct, but most people use them interchangeably.)</span></p><p><span style="font-weight: 400">The symptoms of dehydration include thirst, dark urine, low urine volume, dry skin, fatigue, </span><a href="https://drinklmnt.com/blogs/health/what-causes-muscle-cramps" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">muscle cramps</span></a><span style="font-weight: 400">, dizziness, nausea, constipation, headache, and irritability. Some of these symptoms are linked to low blood pressure, while some reflect other </span><a href="https://drinklmnt.com/blogs/health/fluid-and-electrolyte-imbalance" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">fluid balance disruptions</span></a><span style="font-weight: 400">.</span></p><p><span style="font-weight: 400">Anything that causes water losses can cause dehydration, </span><a href="https://www.ncbi.nlm.nih.gov/books/NBK555956/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">including</span></a><span style="font-weight: 400">:</span></p><ul><li><span style="font-weight: 400">Excessive sweating from exercise, hot climates, etc.</span></li><li><span style="font-weight: 400">Respiratory water losses from COPD or asthma</span></li><li><span style="font-weight: 400">The use of diuretics, laxatives, and other medications</span></li><li><span style="font-weight: 400">Water losses from kidney disease, hyperglycemia, or other medical conditions</span></li><li><span style="font-weight: 400">GI water losses from diarrhea or vomiting</span></li></ul><p><span style="font-weight: 400">Inadequate fluid intake can also cause dehydration, but healthy adults </span><a href="https://www.ncbi.nlm.nih.gov/books/NBK555956/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">rarely</span></a><span style="font-weight: 400"> make this mistake. Not drinking enough water is primarily a problem for older folks with mobility issues and unreliable thirst mechanisms. If it’s hard to tell you’re thirsty and even harder to get to your water, you’re simply less inclined to drink.</span></p><p><span style="font-weight: 400">This is a crucial point. </span><b>Most people </b><a href="https://drinklmnt.com/blogs/health/how-much-water-should-you-drink-a-day-a-science-based-guide-to-hydration" target="_blank" rel="noopener noreferrer"><b>drink enough water</b></a><b>, and exceeding our natural water needs can be dangerous. </b><span style="font-weight: 400">I’ll return to this topic later.</span></p><p><span style="font-weight: 400">It’s a cliche to say that we’re mostly made of water, but it’s true. (We’re </span><a href="https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body#:~:text=Up%20to%2060%25%20of%20the,bones%20are%20watery%3A%2031%25." target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">about</span></a><span style="font-weight: 400"> 60% water weight.) All that H2O resides inside cells, outside cells, and in-between cells as interstitial fluid.</span></p><p><span style="font-weight: 400">Today, our focus will be on the extracellular fluid—the water that adds volume (in plasma) to your blood. And blood volume influences your blood pressure.</span></p><h2><b>Blood Pressure 101</b></h2><p><span style="font-weight: 400">First, a definition: Blood pressure (bp) refers to the pressure of your blood against the walls of your blood vessels. Pretty straightforward, right?</span></p><p><span style="font-weight: 400">Many factors influence your blood pressure: the pumping of your heart, your </span><a href="https://drinklmnt.com/blogs/health/electrolyte-imbalance-or-deficiency" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">electrolyte status</span></a><span style="font-weight: 400">, your nervous system health, various hormones, and (as we discussed) your blood volume. Lording over this system is an ancient brain structure called the </span><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5509160/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">hypothalamus</span></a><span style="font-weight: 400">.</span></p><p><span style="font-weight: 400">We measure blood pressure with two numbers:</span></p><ol><li><b>Systolic blood pressure:</b><span style="font-weight: 400"> your bp as your heart beats (top number)</span></li><li><b>Diastolic blood pressure:</b><span style="font-weight: 400"> your bp between heartbeats (bottom number)</span></li></ol><p><span style="font-weight: 400">Combined—as in, 110/70—these two figures represent your blood pressure status. Here’s how the American Heart Association </span><a href="https://www.heart.org/en/health-topics/high-blood-pressure/understanding-blood-pressure-readings" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">classifies</span></a><span style="font-weight: 400"> different blood pressures:</span></p><ul><li><b>Normal blood pressure:</b> systolic under 120 AND diastolic under 80</li><li><b>Elevated blood pressure:</b> systolic 120-129 AND diastolic under 80</li><li><b>High blood pressure:</b> systolic 130 or greater OR diastolic 80 or greater</li></ul><p><span style="font-weight: 400">What about low blood pressure? There’s no consensus, but it generally </span><a href="http://delineate" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">refers</span></a><span style="font-weight: 400"> to pressures below 90/60.</span></p><h2><b>Dehydration and Low Blood Pressure</b></h2><p><span style="font-weight: 400">One sign of </span><a href="https://drinklmnt.com/blogs/health/how-to-know-youre-dehydrated" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">moderate-to-severe dehydration</span></a><span style="font-weight: 400"> is low blood pressure. When blood volume drops due to water losses, blood pressure </span><a href="https://www.ncbi.nlm.nih.gov/books/NBK555956/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">drops</span></a><span style="font-weight: 400"> along with it.</span></p><p><span style="font-weight: 400">It’s basic physics. A lower volume of a substance (in this case, blood) will exert less pressure on the vessel (blood vessels) that contains that substance. Think of blowing up a balloon. The less air you blow, the lower the air pressure inside the balloon. Less volume, less pressure.</span></p><p><span style="font-weight: 400">Having low blood pressure is generally undesirable. Why? Because blood shuttles oxygen and other nutrients to your tissues, and maintaining normal blood pressure helps push those nutrients to the right places.</span></p><p><span style="font-weight: 400">The </span><a href="https://www.ncbi.nlm.nih.gov/books/NBK499961/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">symptoms</span></a><span style="font-weight: 400"> of low blood pressure are dizziness, fatigue, lightheadedness, nausea, and blurry vision. In severe cases, low blood pressure can lead to irregular heartbeat and shock.</span></p><p><span style="font-weight: 400">On a practical note, hydrating with water PLUS </span><a href="https://drinklmnt.com/blogs/health/what-electrolytes-do-for-you" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">electrolytes</span></a><span style="font-weight: 400"> is crucial for maintaining a normal blood volume. If you drink too much plain water, you may cause an electrolyte imbalance and exacerbate blood pressure issues. More on that soon.</span></p><h2><b>Can Dehydration Cause High Blood Pressure?</b></h2><p><span style="font-weight: 400">The science is thin, but </span><i><span style="font-weight: 400">chronic</span></i><span style="font-weight: 400"> dehydration </span><i><span style="font-weight: 400">is </span></i><a href="https://academic.oup.com/nutritionreviews/article/73/suppl_2/97/1930742" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">linked</span></a><span style="font-weight: 400"> to high blood pressure. For instance, observational data </span><a href="https://pubmed.ncbi.nlm.nih.gov/12365093/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">suggest</span></a><span style="font-weight: 400"> that folks with diabetes and hypertension (high bp) also tend to have low urine output, a sign of dehydration.</span></p><p><span style="font-weight: 400">One possible mechanism involves a hormone called vasopressin. (Vasopressin is also called antidiuretic hormone because everything in physiology must have at least two names to maximize human bewilderment.) Allow me to explain the physiology.</span></p><p><span style="font-weight: 400">Vasopressin is a fluid-retention hormone. Secreted by the hypothalamus (the brain region that’s always monitoring hydration status), vasopressin </span><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723555/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">acts</span></a><span style="font-weight: 400"> on the kidneys to suppress diuresis. More vasopressin, less pee.</span></p><p><span style="font-weight: 400">But vasopressin has other effects, like making your blood vessels constrict. Imagine a balloon shrinking, but without releasing any air. The air pressure increases. Similarly, dehydration-induced vasopressin release may spike blood pressure.</span></p><p><span style="font-weight: 400">Still, dehydration is one of the last causes I’d blame for high blood pressure. Oftentimes there are more likely culprits at play.</span></p><h2><b>More Likely Causes of High Blood Pressure</b></h2><p><span style="font-weight: 400">High blood pressure continues to bewilder the medical community. About one-third of Americans </span><a href="https://pubmed.ncbi.nlm.nih.gov/31865786/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">have</span></a><span style="font-weight: 400"> this heart disease risk factor, but most cases are labeled “essential hypertension” because we </span><a href="https://www.ncbi.nlm.nih.gov/books/NBK539859/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">can’t identify</span></a><span style="font-weight: 400"> a specific cause.</span></p><p><span style="font-weight: 400">But we </span><i><span style="font-weight: 400">do</span></i><span style="font-weight: 400"> know which factors increase hypertension risk: smoking cigarettes, alcoholism, a sedentary lifestyle, sleep deprivation, genetic factors, a high-sugar diet, obesity, and </span><a href="https://drinklmnt.com/blogs/health/electrolyte-imbalance-symptoms" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">electrolyte imbalances</span></a><span style="font-weight: 400">. Let’s double-click on the last two.</span></p><p><span style="font-weight: 400">When people are obese, they’re also more likely to suffer from chronic inflammation. Unfortunately, this immune-system confusion can </span><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5509160/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">dysregulate</span></a><span style="font-weight: 400"> hormones that govern blood pressure.</span></p><p><span style="font-weight: 400">Electrolyte status (especially for sodium and </span><a href="https://drinklmnt.com/blogs/health/potassium-benefits-and-best-sources" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">potassium</span></a><span style="font-weight: 400">) is also crucial for healthy blood pressure. Consider the following:</span></p><ul><li><span style="font-weight: 400">Excess sodium consumption can elevate blood pressure, but so can sodium deficiency. That’s because sodium-retention, blood-pressure-raising hormones like renin and aldosterone kick in on </span><a href="https://drinklmnt.com/blogs/health/health-risks-of-a-low-sodium-diet" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">low sodium diets</span></a><span style="font-weight: 400">.</span></li><li><span style="font-weight: 400">Low-sodium diets in line with government recommendations are </span><a href="https://faseb.onlinelibrary.wiley.com/doi/abs/10.1096/fasebj.31.1_supplement.446.6" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">correlated</span></a><span style="font-weight: 400"> with </span><i><span style="font-weight: 400">higher </span></i><span style="font-weight: 400">blood pressures in people with otherwise normal blood pressure.</span></li><li><span style="font-weight: 400">Higher potassium intakes are uncontroversially </span><a href="https://ods.od.nih.gov/factsheets/Potassium-HealthProfessional/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">linked</span></a><span style="font-weight: 400"> to lower blood pressures. Unfortunately, only <a href="https://www.ncbi.nlm.nih.gov/books/NBK545438/#:~:text=The%2075th%20percentile%20of%20usual%20potassium%20intake%20exceeds%20the%20potassium%20AI%20for%20most%20adult%20DRI%20age%2C%20sex%2C%20and%20life%2Dstage%20groups%2C%20indicating%20that%20between%20one%2Dquarter%20and%20one%2Dhalf%20of%20U.S.%20and%20Canadian%20adults%20exceed%20the%20AI%20(see%20Table%207%2D4)." target="_blank" rel="noreferrer noopener">20–40%</a> of Americans achieve the National Academy of Medicine (NAM) <a href="https://www.ncbi.nlm.nih.gov/books/NBK587683/" target="_blank" rel="noreferrer noopener">adequate intake</a> of 3.4 g/day in men and 2.6 g/day in women. Adequacy is great and all, but it appears that the range of <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6181280/" target="_blank" rel="noopener">3.5–5 g/day</a> could produce even more benefits with little to no downside if you have healthy kidneys.</span></li></ul><p><span style="font-weight: 400">So if you want to improve your blood pressure, you’ll want to get your electrolytes dialed in. Let’s review a practical hydration strategy now.</span></p><h2><b>How To Stay Hydrated</b></h2><p><span style="font-weight: 400">The goal of your hydration strategy should be two-pronged:</span></p><ol><li><span style="font-weight: 400">Get enough fluids</span></li><li><span style="font-weight: 400">Get enough electrolytes, especially </span><a href="https://drinklmnt.com/blogs/health/is-sodium-good-or-bad-for-you" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">sodium</span></a></li></ol><p><span style="font-weight: 400">Most people focus on the first prong only. Following homespun wisdoms like the 8×8 rule (8 glasses of 8 ounces of water per day), they drink beyond thirst in a misguided effort to prevent dehydration.</span></p><p><span style="font-weight: 400">Unfortunately, this can disrupt the second prong. Why? Because drinking plain water beyond thirst </span><i><span style="font-weight: 400">dilutes </span></i><span style="font-weight: 400">blood sodium levels, leading to an electrolyte imbalance called </span><a href="https://drinklmnt.com/blogs/health/hyponatremia" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">hyponatremia</span></a><span style="font-weight: 400">.</span></p><p><span style="font-weight: 400">As you’ll recall, sodium disturbances drive blood pressure disturbances. Healthy hydration isn’t just a matter of drinking adequate fluids per thirst, but also consuming enough sodium to meet baseline needs (about 5 grams per day) and to replace sweat losses (up to double or triple the baseline).</span></p><p><span style="font-weight: 400">Drinking </span><a href="https://drinklmnt.com/blogs/health/electrolyte-water-benefits-and-best-sources" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">electrolyte water</span></a><span style="font-weight: 400"> is a snappy solution to this problem. When you add sodium to your fluids and drink to thirst, you simultaneously prevent dehydration and electrolyte issues. Simple as that.</span></p><p><span style="font-weight: 400">Hey, that’s why we created </span><a href="https://drinklmnt.com/products/lmnt-recharge-electrolyte-drink" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">LMNT</span></a><span style="font-weight: 400">. It’s a convenient electrolyte drink mix with enough sodium to move the needle for your hydration needs. LMNT tastes so good you won’t believe it’s sugar-free. My whole family (including my daughters) is addicted to the stuff.</span></p><p><span style="font-weight: 400">The bottom line? When you get your hydration handled, many problems (including a minority of blood pressure problems) may handle themselves. I’ll drink a tall glass of electrolyte water to that.</span></p>