"Water, taken in moderation, cannot hurt anybody" is a quote attributed to US author and humorist, Mark Twain. The series of articles in this special issue suggest that water in moderation may not be enough for optimal health and wellness, and the authors push the boundaries of what is currently known about water in maintaining health and preventing disease. The Hydration for Health Conference, sponsored by Danone Waters, brought together international experts to review what is known about water consumption and health or, more appropriately, what is not known about water intake and health. One of the key drivers of the interest in water and health appears to be the global obesity epidemic affecting developed and developing countries, young and old alike, but there are other health problems that might be reduced or eliminated if optimal water consumption was known and practiced.
Water is something we take for granted unless the extremes of water intake make headline news. At one extreme of water intake is dilutional hyponatremia, referred to as water intoxication. In 2007, a young wife and mother of 3 children died of water intoxication by participating in a Sacramento, California, radio contest, "Hold Your Wee for a Wii." The contestant who could drink the most water without urinating was promised to win the hottest electronic game of 2007-Nintendo's Wii. She drank about 6 L of water in 3 hours and complained on-air to the disc jockeys that she had a splitting headache- a sign of brain swelling associated with hyponatremia.1 She did not win the contest, called in sick to work, went home, and died later that day in her home. (In 2009, a jury awarded her family $16 million in damages.)2
On the other extreme is insufficient water intake. Three people died in 2009-two of heat stroke and one of multiple organ failure-in a Camp Verde, Arizona, sweat lodge. The "leader" of the sweat ceremony encouraged the participants to push through their discomfort and "shamed" those who wanted to leave. The retreat leader was charged with manslaughter.3
Although these extreme examples make the news, many people seem to practice 2 other extremes-either we don't think at all about water intake, or we ascribe magical properties to water intake. One Web site claiming the virtues of water shouts in all caps, "You're not sick, you're thirsty," and goes on to attribute every major and minor illness with low water intake. If only it was that simple…
While reading these articles, I was struck by 3 themes. The first is that water is an essential nutrient. Of course, that is something that every health professional knows, but as Kavouras and Anastasiou note, water is often overlooked, even though it is the "quintessential" nutrient. As a registered dietitian, I focused much of my attention, and therefore the attention of patients and clients, on the energy-containing macronutrients of carbohydrate, protein, and fat. In weight management, special effort is given to calculate precise ratios of macronutrients to achieve body composition goals, and yet a specific water intake is rarely prescribed. Stookey's article on drinking water and weight management reviews some interesting findings about beverage choices. When calorie-containing beverages are consumed before a meal, individuals do not eat less food to make up for the calories consumed from the beverages. In a recent study,4 researchers found that the simple addition of 2 glasses of water consumed before meals resulted in a greater loss of weight in middle-aged and older adults compared with a group who did not drink water. Both groups were on a restricted calorie diet, but the addition of water before meals resulted in a 44% greater decrease in weight after 12 weeks. Stookey argues that water is the preferred beverage because it results in greater fat oxidation and could reduce total energy intake in both adults and children by 10%, which could have major consequences for weight loss and maintenance.
Lafontan's article points to sugar intake in beverages as the culprit in obesity. The reasoning is based on both epidemiological evidence and biological mechanisms. The epidemiological association between the introduction of high-fructose corn syrup and rise in obesity and diabetes in the United States has been debunked by many researchers, yet the biological mechanisms put forth by Lafontan are of interest. Sugar and sweet foods introduced early in life may cement the desire for sweet foods throughout life, and increased adipose cells in childhood may predispose a child to a lifelong battle with obesity. However, calories do count, and whereas other authors have addressed the role of calories in sweetened beverages, Lafontan argues that sugar, particularly fructose, is the chief problem in the obesity crisis.
The second theme to emerge from these articles is the inverse relationship between the essentiality of water and how little we know about how much we consume, how much is recommended by national associations or government agencies, and how challenging it is to study water in free-living populations. Le Bellego and colleagues point out that even well-recognized recommendations on water intake vary greatly. Reviewing fluid intake recommendations from various organizations across the globe reveals ranges that span 1500 to 2200 mL/d for women and 1500 to 3000 mL/d for men. The authors also point out how difficult it is to accurately measure daily water intake; if recording food intake is difficult for individuals, accurately recalling and recording fluid intake are even more difficult. Indeed, counseling athletes, who are usually well aware of the importance of hydration on performance and health, is challenging when talking about measuring fluid intake. Eight ounces or 1 cup or 240 mL is meaningless to many athletes, and fluid recommendations often need to be communicated with visual reminders (ie, "your team sports bottle holds 5 cups of water").
Finally, the idea that water may play a role in many aspects of human physiological functions from kidney stone formation to human behavior is intriguing. Although hydration and physical activity go together like a hand and glove, Peronnet reviews the importance of water in human performance and argues that water, not electrolytes or carbohydrates, is the preferred fluid during exercise. He points out that many exercise for weight loss, and consuming carbohydrate-containing sport drinks may negate the calorie-burning exercise and defeat the purpose of exercise. He suggests that water is the beverage of choice for those who exercise for 90 minutes or less. A distinction is inferred between athletes and exercisers, and most professional organizations recommend the use of sport drinks for athletes who exercise greater than 60 minutes, especially in hot and humid environmental conditions. On the other hand, would a recreational exerciser be able to exercise longer and recover more rapidly if he/she consumed a sport drink?
Tack reviews the effects of water intake on kidney function and discusses the importance of water intake for 2 troubling conditions: kidney stones and urinary tract infections (UTIs). Although the popular media likes to tout cranberry juice for its ability to help prevent and treat UTIs, water is more likely the preferred beverage choice. Individuals who are prone to kidney stone formation and UTIs are encouraged to drink more water to prevent the recurrence of these disorders. Unfortunately, many older adults who experience nocturia (nighttime urination) curtail water intake in the evening to prevent getting out of bed during the night (and risking a fall) to urinate.
The most interesting question is what does water intake have to do with our brain function? Dehydration affects physical performance, so it makes sense that it affects cognition. Lieberman points out that there are more questions than answers to what we know about hydration and cognition, but he gives us reason to try to tackle the methodological issues needed to understand this complex relationship. Dehydration can affect mood states; for athletes, there are good reasons to talk about mental performance in addition to physical performance with adequate hydration.
Armstrong both introduces and summarizes the articles in this issue; he suggests some new paradigms and future directions for studying water-from both the biological perspective to a public health perspective. The Mexican public health recommendations for national beverage guidelines could be adapted by other nations as we learn more about water and health. Until then, drink up.