Water Intake

DO YOU DRINK ENOUGH WATER?

Consumer Reports on Health November 1999

A well-conditioned NBA rookie, a 34-year-old businesswoman, and a 58-year old executive recently retired. Each complained of the same symptoms: muscle cramps, headaches, and fatigue, especially near the end of the day. In each case, Susan Kiciner, Ph.D., a registered dietitian in Seattle, suspected the same problem: too little water. "They were all somewhat dehydrated, just dehydrated enough to make their days a little miserable." In each case, a simple water prescription cured the problem.

Those cases are hardly unique. In fact, most people consume less than the optimal amount of water and a significant number of them do experience symptoms. Moreover, a skimpy water intake may cause more than just symptoms. It clearly contributes to constipation and increases the risk of heat exhaustion or heat stroke. It probably helps cause or worsen asthma, dental disease, kidney stones, and urinary-tract infections. It may even increase the risk of colds and cancer.

Insufficient water intake is a particular concern for older people, because aging, certain drugs (notably sedatives and tranquilizers), and certain diseases (such as diabetes and stroke) may all weaken the sense of thirst. In fact, dehydration is one of the top ten reasons why older people are hospitalized. Young or old, you need to know whether your body requires more water and whether wetting your whistle more could really help your health.

Water shortage
The body is constantly losing water via the breath, skin, urine, and feces; the more you weigh, the more water you lose. On a cool, inactive day, the average man loses about 12 eight-ounce cups of water, but takes in only about 9 cups (about half of that from the water in fruits, vegetables, and other solid foods). The deficit eventually triggers enough thirst to restore water equilibrium, but the average man still spends most days slightly dehydrated.

The average woman experiences a somewhat smaller deficit: about 9 cups lost on a cool, quiet day, but only about 7 1/2 cups consumed. However, that 1 1/2 cup shortfall matters more for women, since they generally weigh less than men.

The damage from dryness
Severe dehydration - a net water loss of as little as 4percent of body weight - can make blood volume and blood pressure plummet, potentially causing muscle spasms, dimmed vision, delirium, fainting, or even a heart attack.

Such drastic problems are relatively rare, since thirst typically kicks in when water loss hits about 2 percent of body weight. But some people may start feeling symptoms of mild dehydration including headache, fatigue, lightheaded, muscle cramps, and slightly dulled thinking after just a 1 percent loss. And the average man's daily water deficit does reduce body weight by about that much; some women with a slightly higher-than-average deficit may also feel the effect of their water shortage.

In addition, some evidence suggests that consuming an ample amount of water may provide more important health benefits possibly including protection against a common killer.

• Reduced cancer risk. Consuming plenty of fluids can speed the elimination of feces from the colon and urine from the bladder, thereby helping to prevent and treat constipation and urinary tract infection. Researchers now suspect that getting enough fluid might cut the risk of cancer, mainly by flushing out or diluting carcinogens in the bladder and colon.

While that notion is still just theoretical, observational studies do lend some support. In the largest one, a ten-year Harvard study of some 50,000 men, published last May in The New England Journal of Medicine, those who consumed the most fluid had roughly half the bladder cancer risk of those who consumed the least. Two smaller, earlier observational studies linked a low fluid intake with an increased risk of bladder or urinary-tract cancer; another suggested that drinking at least five glasses of water a day might cut the risk of colon cancer. One very small study even linked consumption of water, but not that of other beverages, with a reduced likelihood of breast cancer possibly because water may help wash away or dilute carcinogens not only in the bladder and colon but also in individual cells through out the body.

• Less chance of kidney stones. Stones form when calcium, uric acid, and other substances in the urine become sufficiently concentrated to form crystals. Drinking lots of liquids helps prevent stones, presumably by keeping those concentrations low. People who've already had kidney stones need as much as two extra quarts of water a day, according to some research, to prevent recurrence.

• Fewer asthma attacks. Researchers have long known that people with asthma have more trouble breathing when it's dry outside, presumably because parched airways don't function properly. Researchers from the University of Buffalo recently showed that lung function declines when asthmatic individuals get dehydrated, increasing the chance of asthma symptoms even in humid weather. (Dehydration similarly dries the mucus membranes in the nose and throat, reducing their ability to trap airborne bacteria and viruses. So dehydration just might increase susceptibility to colds and other respiratory infections.)

• Better oral health. Saliva helps neutralize the cavity-causing acids in the mouth, wash away food particles and sugars, and inhibit the growth of microorganisms that cause gum disease andother oral problems. Even slight dehydration can reduce saliva. Some people try to moisten their mouth by chewing gum or sucking candy or lozenges rather than by drinking more. But unlessyou're using sugar-free products, such sugary items compound the risk of cavities and, of course, they still leave you dehydrated.

• Reduced weight. In theory, drinking more water, especially with meals, may help curb the appetite by making you feel fuller. While there's no supporting evidence, that simple step is certainly worth trying if you want to slim down.

In addition, some people tend to eat rather than drink when they're thirsty, for two possible reasons. Many foods make you feel less thirsty, since they containsome water and relieve dryness in the mouth by stimulating salivation. And some people simply confuse thirst with hunger. Deliberately drinking more can rectify the problem.

Water, water, everywhere
Getting more than the minimum water requirements may possibly provide additional benefits. In general, the only people who may be harmed by consuming too much fluid are those whose body retains water due to congestive heart failure, hypothyroidism, or long-term use of certain medications, notably nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, ketoprofen, and naproxen. In addition, men with an enlarged prostate should weigh the possible benefits of ample hydration against the likely inconvenience. But while all those people should avoid drinking excessive amounts of water, they should still try to consume the recommended amount. Nor do people who take diuretics need toworry that the recommended intake of water will interfere with their medication.

You can get your water from a combination of beverages and solid foods. But it probably makes sense to get at least five 8-ounce cups from water itself, partly because it's cheap and calorie-free,and partly because some of the cancer evidence suggests greater protection from water than from other drinks. Other good sources include healthful beverages such as 100 percent fruit juiceand low-fat milk or soup. Noncaffeinated soft drinks and fruit drinks also count toward your total, but they're loaded with sugar. And caffeinated or alcoholic drinks don't count at all, since caffeine and alcohol are diuretics, they boost urine output and could leave you more dehydrated than before.

Fruits and vegetables are the best food sources of fluid: Each serving of produce typically provides about one-third of a cup of water. A serving of red meat, poultry, or fish usually provides about one-fourth of a cup; a serving of grain provides about one-sixth of a cup.

Because you may start feeling symptoms of dehydration before you start feeling thirsty, particularly if you're older, don't rely on thirst to guide your water intake. Instead, drink steadily over the course of the day.You can tell you're getting enough fluid if your urine is clear or very pale yellow and virtually odorless; dark-yellow, strong-smelling urine means you need to drink more.

Summing Up
Most people, particularly men, don't consume enough water. The evidence that the resulting deficit may keep you from feeling your best or may help promote or worsen various health problems including constipation, urinary-tract infection, kidney stones, asthma, dental disease, and possibly even colds and cancer-is not conclusive. But boosting your fluid intake is so cheap and simple that even a slight possibility of payoffs make that step a good idea for most people.

Try to consume at least 9 to 12 cups of fluid a day, depending on how much you weigh (see below).Drink extra water when you exercise, when it's hot or dry inside or outside, and in the other special situations described in the box. Aim to get at least half your quota from water itself, the restfrom healthful beverages or solid foods, especially fruits and vegetables.

How much water do you need?
To calculate the minimum daily amount of water you should be getting from all sources, follow these steps:

1. Enter your weight pounds
2. Multiply line one by .04 pounds of water lost
3. Multiply line two by 2 cups of water needed

The following factors increase the amount of water you should consume:

• Exercise. In cool weather and for ordinary exercise like walking, drink one cup, 8 ounces, of water beforehand, an additional 4 ounces every 20 minutes or so during the activity, and another8 ounces within a half-hour after the workout. Step up your intake when you're exercising harder or the weather's hot. And drink more than you need to satisfy your thirst after the workout.

• Height, heat, and humidity. The reduced humidity at high elevations and in dry weather increases the amount of water you lose through respiration and perspiration. And you obviously sweat more when it's hot out. To compensate, consume an additional one or two cups of water a day when the elevation exceeds 5,000 feet, the temperature exceeds 80°F or so, or the humidity isunusually low. Note that indoor air can be quite dry, due to heating in winter or air conditioning in summer.

• Pregnancy and breast-feeding. Pregnant women need at least one extra cup of water a day. Breast-feeding mothers need an additional three to four cups.

• Caffeine and alcohol. Those substances may pull as much water out of you as they put in, or possibly even more. To be on the safe side, consume an extra half-cup of water for every cup of caffeinated or alcoholic beverages you drink.

• Diarrhea or fever. Try to consume an additional 2 to 3 quarts of water per day when you have diarrhea, and an extra cup for every degree of fever.