May 30, 2024

What Happens to Your Body When You’re Dehydrated

About Nicole Pajer

Nicole Pajer is a Los Angeles-based freelance published in The New York Times, Woman's Day, AARP, Parade, Wired, Glamour, People and more.

Water is vital to our overall health. It plays a critical role in every major body system, including transportation of nutrients and waste, regulation of body temperature, and protection of joints and organs. Dehydration occurs when we lose more fluids than we take in, which may lead to serious health consequences.

Homeostasis is the body’s ability to maintain a stable and relatively constant internal environment, ensuring its optimal performance. This is no small feat when it comes to hydration because water is lost through everyday bodily functions such as breathing, metabolism and waste removal. Physical activity and sweating increase water loss even further. To preserve homeostasis, our bodies have an internal system of checks and balances to safeguard against dehydration, including water reserves, reabsorption of water through the kidneys and the sensation of thirst.

Water reserves

Our body’s first line of defense against dehydration is its large water reserves. Water is the most abundant molecule in our cells, comprising more than 70% of an infant’s body mass. These reserves act as a buffer and compensate for temporary decreases in water intake, allowing us to maintain proper hydration levels without experiencing adverse effects.

Water reabsorption through the kidneys

The kidneys work to filter the blood, regulate blood pressure and remove waste. It’s through the filtering process that the kidneys return about 200 quarts of fluid back to the blood every 24 hours—that’s about 50 gallons! When water intake decreases, the kidneys reabsorb more water, concentrating the urine, to ensure proper hydration levels are maintained. Concentrated urine will appear darker in color and may be an early warning sign of dehydration. Urine color, however, can also be affected by certain medications.

Sensation of thirst

Sensation of thirst serves as the third line of defense against dehydration. We’ve all experienced that craving—maybe after working outside in the hot sun—for an icy cold glass of water. That sensation is our body’s way of telling us that it needs fluids.

Dehydration and seniors

As we age, these internal defenses have packed their bags and retired somewhere exotic. So, what does that mean for older adults? It means they are at greater risk for dehydration. Older adults have diminished water reserves—approximately 20-30% less compared to children—making them more vulnerable to dehydration with even minor fluid loss. Kidney function also declines with age, impairing their ability to reabsorb water, which leads to a significant loss of fluids. Furthermore, older adults may not feel thirsty due to a diminished thirst sensation, causing them to drink less water. Outside factors such as chronic disease and certain medications can compound the problem even further. The body’s checks and balances are no longer as effective as they once were, meaning older adults must make a conscious effort to add more fluids to their diet.

The effects of dehydration

Dehydration impacts every major system of the body and is associated with serious side effects for older adults.

Kidneys and urinary tract

Older adults are among the most likely to develop a urinary tract infection (UTI) but are the least likely to experience the textbook symptoms of pain during urination, urgency to go, or fever. Instead, a sudden change in behavior is a much more common symptom of UTI in older adults but may be misdiagnosed as a cognitive or memory issue, delaying the proper diagnosis even further.

Brain

All the cells in our body, including our brain cells, require water to function properly. The brain does not store water and because water reserves are already diminished in older adults, continuous hydration is imperative for proper brain function. Dehydration causes brain cells to shrink in size and mass leading to brain fog, memory issues, confusion and disorientation.

Cardiovascular and circulatory systems

Water makes up about 50% to 80% of our blood and is therefore crucial to the body’s mission of homeostasis. Blood volume is the total amount of fluids within the circulatory system (heart, arteries, capillaries, veins, and venules) at any given time. Proper blood volume enables the delivery of oxygen, nutrients, and hormones to all major systems of the body. Blood volume and blood pressure are interconnected, so during dehydration, as the water content of blood decreases so does blood volume and blood pressure. Low blood pressure prevents the heart from pumping enough oxygen to the brain which can result in dizziness and fainting, leading to more falls.

Muscles

Water makes up about 76% of our muscle mass, making it the main reservoir of water in the body. To protect vital organs such as the brain and liver, acute dehydration mainly affects the skin and muscles. Muscle is responsible for the majority of glucose metabolism and water plays a critical role in triggering metabolism. Water loss impairs normal muscle function and is a factor in the development of insulin resistance and type 2 diabetes.

Skin, hair and nails

The integumentary system, in particular the skin, is integral for temperature regulation in the body and water plays a large role in this. The body absorbs heat, distributing it among the fluids in the body (like water!), which then evaporates in the form of sweat through the skin. This is especially important for older adults who are unable to adjust to sudden changes in temperature and are at greater risk for heat stroke.

Preventing Dehydration

The National Council on Aging recommends drinking one-third of our body weight in ounces of water each day. For example, a 150-lb person should drink 49.5 ounces of water per day (150 x 0.33 = 49.5). Certain health conditions along with various medications may necessitate an increase in water intake, so it is important to talk with your doctor about what is appropriate for you. In addition to drinking more water, eating foods with a high-water content such as watermelon, cucumber, lettuce, strawberries, celery and low sodium soups, broths and stews can also help to stave off dehydration. When so much is resting on fluid intake, it’s important to make every drop count.

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