Drink to Your Health

Hydration and Your Health

Water plays a crucial role in overall body health, but tales of near-universal dehydration seem to be exaggerated.

Water, water everywhere: Water is by far the largest constituent of the human body, making up about 60 percent of your total body weight. This large pool of water performs many crucial functions. Among them: It nourishes the cells; carries food throughout the body; eliminates waste; regulates body temperature; cushions and lubricates the joints; and maintains blood volume and blood pressure. Inadequate levels of fluid consumption have been associated with kidney stones, and higher rates of: urinary tract infections; bladder and colorectal cancers; and even heart disease in one or two studies.

Universal agreement: Given the above, all experts agree that an adequate water supply is crucial to the body's optimal functioning. The only question: How much water and other fluids do you need to drink per day?

The 8 x 8 myth: Most American adults believe that they should drink eight 8-ounce glasses of water a day. Why do they believe this? Because they have heard it countless times from all U.S. media, including this magazine. But there's little to no evidence supporting 8 x 8.

The good professor: Last summer a Dartmouth College professor named Heinz Valtin published a lucid and compelling article in the Journal of the American Physiological Society. Basically, Valtin committed himself to searching out medical-scientific verification for the 8 x 8 rule. He couldn't locate any.

"I have found no scientific proof that we must drink at least eight glasses of water a day," concluded Valtin, the professor emeritus of physiology at the Dartmouth Medical School. "The published data strongly suggest that we probably are drinking enough, and possibly even more than enough."

Of course, Valtin was researching the hydration habits of average, nonexercising Americans. Runners sweat heavily, and need to drink more than nonexercisers. And the heavier and more muscular you are, the hotter the temperature, and the faster you run, the more you will sweat.

Awash in water: Meanwhile, a survey of 2,818 adult Americans in 2000 by the International Bottled Water Association (IBWA) revealed that we are drinking 17.6 8-ounce cups of liquid a day. The IBWA argues that 6 cups of this amount is alcohol and caffeine drinks (both considered diuretics, meaning they increase urine production), and should therefore be subtracted from the total.

The truth about caffeine: However, research conducted in the last 2 years has reversed the age-old wisdom that caffeinated beverages are diuretics. Actually, to be more precise, the research confirmed that caffeinated beverages are diuretics--to the same degree as plain water. You drink a lot of water, you need to go potty. Same with caffeinated beverages, no more, no less.

"The research indicates that caffeine stimulates a mild diuresis similar to water," says heat and hydration expert Larry Armstrong, Ph.D., author of the just published Exertional Heat Illnesses. Armstrong reached this conclusion after analyzing 10 medical articles on caffeinated beverages, and published his report last year in the International Journal of Sport Nutrition and Exercise Metabolism.

Beating a path to the bathroom: Other experts agree with Valtin and Armstrong: There's no dehydration epidemic sweeping the country. If anything, we're overhydrated. This isn't necessarily a bad thing. It's probably just adding to your daily mileage and calorie burn, courtesy of all those trips to the bathroom.

But there's no evidence for the list of dehydration ills--fatigue, headache, dry skin, lack of concentration, and so on--put forth by some. "Without any convincing data, I remain skeptical of all these so-called dehydration problems," says Penn State University nutrition researcher Barbara Rolls, Ph.D., author of Thirst, and one of the country's leading experts on hydration. "It's a myth that's being perpetuated. The thirst mechanism is exquisitely tuned to keep us in fluid balance."

This just in: While most Americans seem to be consuming plenty of fluids, some still haven't gotten the message, including some regular exercisers. In late April, a study presented at the annual meeting of the IDEA Health & Fitness Association showed that nearly half of all exercisers at several Bally Total Fitness locations were dehydrated before their workouts.

Mars and Venus: When it comes to sweat rates and fluid-replacement needs, men and women come from different planets. Because men are on average significantly heavier than women and have more muscle mass, they sweat more than women, and need to drink more. Or, to turn things around: Women don't sweat as much as men, and don't need to drink as much.

An overlooked truth with real-life consequences: For the reasons just stated, a woman's hydration need can be up to 30-percent less than a man's. This essential fact has been largely overlooked in most articles on hydration needs, and it's particularly important for women runners, because most of the marathoners who suffer from hyponatremia (excessive fluid consumption), including a number who have died from marathon-related hyponatremia, have been women. More on that later.

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