Myth-information about caffeine and dehydration

Sep 18, 2012 by Carol Bareuther

Some people think that caffeine is a potent diuretic. True, if you drink a cup of coffee in the morning, you’ll soon be looking for a restroom. Yet, the myth persists that drinking coffee or cola or other type of caffeine-containing beverage will dehydrate you, especially if you drink it and work or exercise in hot weather. This is simply not true, although there are other ways you can become dehydrated.

The myth-information about caffeine and dehydration was busted back in 2003 when researchers at Loughborough University in the United Kingdom conducted a literature search of articles published in medical and scientific literature from 1966 to 2002. What they discovered on the topic was that drinking a large amount of caffeine in large doses, for example two to three cups of coffee or five to eight cups of tea at once, results in a short-term increase in the amount of urine in those folks who haven’t taken in any caffeine in any form for several days or weeks. However, they found that chronic caffeine consumers developed a tolerance to this diuretic effect. In fact, caffeine equal to the amount normally found in a standard cup of coffee, tea or soft drink didn’t act like a diuretic at all in those accustomed to caffeine. What this means is that drinking a refreshing glass of iced tea on a hot afternoon will not dehydrate you, but instead provide re-hydrating fluids.
What can lead to dehydration is not drinking enough fluids. According to the American Council on Exercise (ACE), women should consume 91 ounces (about 12 cups or 3 quarts) and men, 125 ounces (about 16 cups or 4 quarts) each day. This doesn’t need to be all as water, but in a variety of fluids including coffee, tea, juice, smoothies and soups. Even fresh fruits and vegetables are a great source of fluid. For example, cantaloupe, grapefruit, strawberries and watermelon, all provide more than 90 percent of their weight as water, as do a long list of vegetables such as broccoli, cabbage, cauliflower, celery, cucumbers, eggplant, lettuce, bell peppers, radishes, tomatoes and zucchini squash.
Fluid needs do increase in hot weather. In fact, one hour of work or exercise in the heat can lead to the loss of a quart or more of fluid through sweat. In this case, the ACE recommends drinking 2 to 2 ½ cups (16 to 20 ounces) of water two to three hours before the start of exercise. Then, drink another cup (8 ounces) a half hour prior to the activity, and then a cup (8 ounces) every 10 to 20 minutes while performing the work or exercise. It’s important to drink throughout the activity as thirst can be a sign that dehydration is already setting in. Interestingly, rehydration occurs faster with sodium, regardless if this is in the form of salt sprinkled on food or in a sports drink. With the amount of salt in our regular diets, there is no need to take salt tablets.
Eating a high protein diet can cause dehydration. That’s because your body needs extra fluids to get rid of the urea produced by all the protein. High-protein containing foods include meats, poultry, fish, eggs and dairy products as well as more unnatural forms of protein such as protein powders and protein shakes.
Drinking alcohol, including beer and wine, can also be dehydrating. This is due to alcohol blocking the release of a hormone called antidiuretic hormone, or ADH, and thus causing the kidneys to excrete more urine. Research has shown that the equivalent of a 2-ounce shot of liquor can result in the loss of up to 1 cup or 8 ounces of urine.
Dehydration sounds simple, but can have lethal consequences. Take care to prevent it by taking in enough fluids – including coffee and tea – and high-fluid foods each day, while not going on high-protein diets or binge drinking on alcohol.

Carol Bareuther is a freelance writer in St. Thomas. Comments on this story are welcome at