A well-conditioned NBA rookie. A 34-year-old businesswoman. 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 Kleiner,
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 4 percent 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, lightheadedness, 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 effects 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 throughout 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 micro-organisms that
cause gum disease and other 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 unless you'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 contains some 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
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 to worry 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 juice and 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.
Drink extra water when you exercise, when it's hot or dry inside or outside, if
you’re pregnant or breast-feeding, when you consume alcohol or caffeine, or have
diarrhea or fever. Aim to get at least half your quota from water itself, the rest from
healthful beverages or solid foods, especially fruits and vegetables.
This article was excerpted
from Consumer
Reports on Health.
Copyright © Consumers Union of U.S., Inc.,
2000
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