Hospitals across the country are bracing for an increase in emergency calls related to dehydration and heat illness as extreme temperatures persist. The key to preventing dehydration, a dangerous loss of body fluids often triggered by heat exposure, is to replenish fluids every hour or so, experts say. Sports drinks containing electrolytes like sodium, lost through sweat, are recommended over plain water in many cases.
How the Body Becomes Dehydrated in Hot Weather
The human body is composed of about 60% water, which is constantly lost through breathing and sweating. Heat amplifies this process, and without adequate fluid replacement or access to cool air, the body cannot compensate for the loss, leading to dehydration, explained Dr. David Della-Giustina, a Yale Medicine emergency medicine physician and director of the school's wilderness medicine fellowship program.
As the body sweats, heart rate increases and blood is shunted to the skin to dissipate heat. This cooling effort paradoxically generates more internal heat. "As you get hotter, you can sweat more profusely and then you start losing fluids and electrolytes through your sweat, and if you don't drink enough or you're sweating more than you're drinking, you can start to get dehydrated," said Dr. Teresa Murray Amato, chair of emergency medicine at Long Island Jewish Forest Hills in New York.
When dehydration sets in, symptoms include thirst, dry mouth and lips, nausea, lightheadedness, headache, and dark-colored urine. Dehydration often accompanies heat-related illnesses such as heat cramps, heat exhaustion, and heat stroke. In heat exhaustion, the body loses its ability to cool itself because of extreme external heat, leading to rapid heartbeat, low blood pressure, and altered mental status.
How Quickly Can Dehydration Occur?
Those at highest risk include people engaged in outdoor activities like exercise, yard work, or construction. Dehydration can develop within hours, and sometimes as fast as 30 minutes, according to Della-Giustina. "People can lose a liter or two of water in a period of an hour or two if they don't replace it," he said. For those sitting in a hot apartment without exertion, it takes longer—several hours at least—to become dehydrated.
Risk factors include age (the very young and elderly have a harder time cooling off) and certain medications. Many older adults take drugs that increase dehydration risk, such as antihistamines, NSAIDs like ibuprofen, and diuretics. Temperature and humidity also play a role; the body cools through sweat evaporation, which is hindered on humid days. "On a humid, hot day, no matter how much you're sweating, you can't get sweat to evaporate and therefore cool your body," Amato said.
How to Prevent Dehydration in Hot Weather
Stay out of the heat as much as possible. Drink fluids regularly, about every hour. Della-Giustina noted that the old advice of six to eight glasses of water daily is not universal; fluid needs vary. Use urine color as a guide: clear urine indicates good hydration, while darker urine signals dehydration. "Once you get to the point where you're feeling thirsty, you're already down 1%-2% of your body water, which is really significant, and it gets really hard to catch up," he said.
If you notice signs of dehydration—dark urine, nausea, or lightheadedness—move to a cool place with air conditioning or a fan and drink fluids. Aim to drink every 15 minutes. Surprisingly, plain water is not the best choice. Sweat loss includes electrolytes, so replenishing sugar and sodium is crucial. "If you're rehydrating strictly with water and not replacing those electrolytes, you actually aren't helping yourself," Amato said. Sports drinks are optimal, according to Della-Giustina. Avoid diet sports drinks because sugar helps the stomach absorb water; if the drink is too sugary, dilute it with water. A cheaper alternative: mix half a teaspoon of salt and six teaspoons of sugar in a liter of water.
Symptoms should improve within 15 to 30 minutes. If they worsen, seek medical care at a hospital or urgent care center. Heat is a leading cause of dehydration, which can become life-threatening if untreated. Drink before you are thirsty, stay out of the sun, and carry a sports drink if you must be outdoors.
This story was originally published on HuffPost.
