Drink Up—It’s Hot Out There

Tufts nutrition experts give advice on how to stay hydrated when the temperatures soar
illustration with people drinking water
Healthy people typically need to consume fluid just until they are no longer thirsty, often referred to as “drink to thirst.” Illustration: Peter Grundy
July 28, 2016

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Here, in no particular order, are some thirst-quenching things to keep in mind when the mercury rises, according to Elena Naumova and Edward Saltzman, both professors and academic deans at the Friedman School. Saltzman, a physician, is also a scientist in the Energy Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging. Naumova, who is also an adjunct professor at the School of Medicine, points out that dehydration is particularly dangerous for senior citizens, thousands of whom are hospitalized in the United States each year with heat-related illnesses, at a cost of about $27 million annually.

Take it easy. When it’s hot, our bodies don’t respond to physical activity as well. High humidity further impairs your body’s response. The best way to avoid dehydration and other types of heat-related injury to is kick back when the temperature is higher than usual. If you have cardiovascular disease, diabetes, some types of lung disease or a number of other conditions, you are at especially high risk for dehydration and heat-related injury.

Drink when you’re thirsty. Forget the popular wisdom that everyone needs eight glasses of water per day—it’s not based on current science. Healthy people typically need to consume fluid just until they are no longer thirsty, often referred to as “drink to thirst.” But on hot days, do pay attention to the warning signs of dehydration, including lightheadedness, weakness, decreased energy and dark or infrequent urination. If you experience these signs, you should drink more, cease physical activity, get someplace cooler and seek medical attention, especially if you have diabetes or heart disease.

Hydrate in advance. If you anticipate being exposed to hot temperatures, especially if you are going to be physically active, prepare by drinking 1 to 1.5 quarts of fluid in the two to three hours beforehand. Consider drinking even more if the activity will be prolonged and strenuous—up to 1.5 quarts for every 100 pounds of body weight.

Drink during heat exposure. The amount of fluid you need depends on your body size, age, gender, the temperature and humidity, and the degree of physical activity. Aim for a minimum of one quart every two to three hours. If you get thirsty, drink more.

Fluid types and temperatures don’t matter. All types of beverages will help you stay hydrated, including water, carbonated beverages, flavored beverages and even milk or hot chocolate. Make sure you have ready access to drinks you like.

Caffeinated drinks are OK in moderate amounts. Contrary to prior belief, there is little evidence to suggest that caffeinated beverages act as diuretics, at least in the amounts that many people consume. But larger amounts, such as more than 16 ounces of coffee or 32 ounces of black tea, may cause you to urinate more, contributing to fluid loss. Also, remember that caffeine may have extra stimulant effects if you drink more than you usually do.

Drink fruit juice and sugar-sweetened beverages in moderation. These beverages help prevent dehydration, but they also contain calories, which can add up quickly when you guzzle them. Very sweet drinks may also make you feel thirstier, a physiological trick of absorbing all that sugar.

Sports drinks aren’t necessary for most people. Unless you engage in strenuous activity in the heat, it is unlikely that drinks that contain carbohydrates and electrolytes such as sodium and potassium will provide a clear benefit over other drinks. These drinks are more likely to benefit athletes who train or compete in hot temperatures.

Fluids in fruit and vegetables count. Non-starchy vegetables and fruit—such as cucumbers, lettuce and, of course, watermelon—contain water, which counts toward your fluid intake. The same is true for foods that are prepared with water, such as soup. But don’t rely on these foods to completely meet your total fluid needs—you still need to drink.

Spicy foods don’t help. Eating spicy foods can make you sweat, which helps dissipate body heat. But it’s likely that being in hot temperatures will have you sweating plenty without the need to reach for the ghost peppers.

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