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Dehydration
A professional athlete — strong, fit and
apparently in excellent health — collapses during a workout on a hot day and
never recovers. The cause of death is dehydration (hypohydration), which occurs
when the body doesn't have enough water to carry out its normal functions.
Although stories of high-profile athletes succumbing on the playing field grab
headlines, such cases are rare. On the other hand, millions of ordinary people
— many of them infants and older adults — die worldwide of dehydration every
year.
What's more, even mild dehydration — as
little as a 1 percent to 2 percent loss of body weight — can cause symptoms
such as weakness, dizziness and fatigue and may have a negative effect on
long-term health. Severe dehydration, usually defined as a loss of 9 percent to
15 percent of body weight, is a life-threatening medical emergency.
In the simplest terms, dehydration occurs
when you lose more water than you take in. Even a slight imbalance causes
serious problems because water is essential to human life: It forms the basis
for all body fluids, including blood and digestive juices; it aids in the
transportation and absorption of nutrients; and it helps eliminate waste.
You can usually reverse mild to moderate
dehydration by increasing your intake of fluids, but severe cases need immediate
medical treatment. The safest approach is not to become dehydrated in the first
place. You can do that by monitoring your fluid loss during hot weather, illness
or exercise, and drinking enough liquids to replace what you lose.
Signs and symptoms
Unfortunately, thirst isn't a reliable
gauge of the body's need for water, especially in children and older adults. A
better barometer is the color of your urine: clear or light-colored urine means
you're well-hydrated, whereas a dark yellow or amber color usually signals
dehydration. Other signs and symptoms vary, depending on the degree of
dehydration, which may be mild, moderate or severe.
Mild to moderate dehydration is likely to
cause:
 | Excessive thirst
| Sleepiness or tiredness — children are
likely to be less active than usual
| Dry mouth
| Decreased urine output — fewer than six
wet diapers a day for infants and eight hours or more without urination for
older children and teens
| Few or no tears when crying
| Muscle weakness
| Headache
| Dizziness or lightheadedness |
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Severe dehydration, a medical emergency,
can cause:
| Extreme thirst
| Extreme fussiness or sleepiness in
infants and children; irritability and confusion in adults
| Very dry mouth, skin and mucous
membranes
| Lack of sweating
| Little or no urination — any urine
that is produced will be dark yellow or amber
| Sunken eyes
| Shriveled and dry skin that lacks
elasticity and doesn't "bounce back" when pinched into a fold
| In infants, sunken fontanels — the
soft spot on the top of a baby's head
| Low blood pressure
| Rapid heart beat
| Fever
| In the most serious cases, delirium or
unconsciousness |
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Causes
If you're an average adult, every day you
lose close to 2.5 liters (more than 10 cups) of water simply by sweating,
breathing and eliminating waste. You also lose electrolytes — minerals such as
sodium, potassium and calcium that maintain the balance of fluids in your body.
And all this is before you even think about mowing the lawn on a sticky
afternoon, working out at the gym or rearranging the living room furniture.
Even when you're active, you normally can
replenish what you've lost through the food and liquids you consume, but
sometimes you eliminate more water and salts than you replace. The result is
dehydration — your system literally dries out. Because water makes up about 60
percent of your body weight, this can cause physiological changes that may
affect your health, even if you don't have noticeable signs or symptoms.
Just a small reduction in body fluids and
electrolytes, for instance, leads to a lower circulating blood volume. As a
result, your heart has to pump harder to maintain adequate blood flow to your
vital organs, and your body is less able to control blood pressure, distribute
nutrients and eliminate waste.
What's more, because blood flow to your
skin is reduced and you have less water in your system, you don't perspire or
dissipate heat the way you normally would. In extreme cases, this can cause your
body core temperature to soar, leading to heat exhaustion and possibly heat
stroke — a potentially life-threatening condition in which your body
temperature climbs to 104 F or more, sometimes reaching as high as 107 F.
Not all cases of dehydration have such
serious consequences, but even a 2 percent loss of body weight can affect
athletic performance, and a 3 percent to 5 percent loss adversely affects
reaction time, concentration and judgment. What's more, dehydration is
insidious; these effects often occur before you're aware of them.
How dehydration happens
Sometimes dehydration occurs for simple reasons: You don't drink enough because
you're sick, busy or just not thirsty, or because you lack access to potable
water when you're traveling, hiking or camping.
Other causes of dehydration include:
| Diarrhea. Severe, acute diarrhea —
that is, diarrhea that comes on suddenly and violently — can cause a
tremendous loss of water and electrolytes in a short amount of time. If you
have vomiting along with diarrhea, you lose even more fluids and minerals.
Children and infants are especially at risk. Worldwide, more than 1.5
million infants and children die of dehydration resulting from diarrhea
every year — 300 to 500 of them in the United States. Most of these deaths
occur in the first year of life.
| Exercise. Every day, athletes of all
ages and skill levels — pint-sized soccer players, treadmill joggers,
professional cyclists and tennis players — experience some degree of
dehydration. The reason is simple: you lose water when you sweat. And
although it makes sense that you sweat more in hot weather, you can also
become dehydrated in winter, especially if you wear layers of insulated
clothing or work out in an overheated gym. Humidity compounds the problem
because it increases sweating and inhibits cooling. Although no one who is
active is immune, preteens and teens who participate in sports are
especially susceptible, both because of their smaller body weight and
because they may not be experienced enough to know the warning signs of
dehydration. Young athletes are also at risk if they don't become acclimated
to heat and humidity before a workout or if they exercise too strenuously in
an effort to make the team.
| Fever. In general, the higher your
fever, the more dehydrated you become. If you have a fever in addition to
diarrhea and vomiting, you lose even more fluids.
| Increased urination. This is most often
the result of undiagnosed or uncontrolled diabetes, a disease that affects
the way your body uses blood sugar and that often causes increased thirst
and more frequent urination. Another condition, diabetes insipidus, is also
characterized by excessive thirst and urination, but in this case the cause
is a hormonal disorder that makes your kidneys unable to conserve water.
Certain medications — diuretics, antihistamines, blood pressure
medications and some psychiatric drugs — as well as alcohol can also lead
to dehydration, generally because they cause you to urinate or perspire more
than normal.
| Long airplane flights. The air in the
cabins of most commercial airplanes is drier than the Sahara Desert, with
humidity levels hovering around 10 percent or less. Compounding the problem
for some people is alcohol — a readily available in-flight beverage. The
longer the flight and the more alcohol you drink, the more dehydrated you
become — it takes 8 ounces of water to make up for every 1.5 ounces of
alcohol you consume. Older adults and people who have diabetes or who take
drugs that increase urination are particularly at risk. The best advice when
flying is to bypass the alcohol cart and drink bottled water instead. Sugary
drinks, coffee and tea aren't ideal substitutes. Although new research
suggests that caffeine-containing beverages aren't as dehydrating as once
thought, water is still your best bet. And don't worry about having to climb
over your seatmates to get to the bathroom — preventing dehydration is
worth a little social embarrassment. In addition to all the other problems
it can cause, a lack of fluids combined with arid airplane air dries out
your nasal passages, increasing your risk of upper respiratory infections.
| Hot, sunny climates. It makes sense that
you perspire more — and therefore lose more fluids — in hot climates.
High humidity makes matters worse because it prevents sweat from evaporating
quickly.
| Burns. Doctors classify burns according
to the depth of the injury and the extent of tissue damage. Third-degree
burns are the most severe, penetrating all three layers of skin, and often
destroying sweat glands, hair follicles and nerve endings. People with
third-degree burns or extensive first- or second-degree burns experience
profound fluid loss, and the resulting dehydration can be life-threatening. |
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Risk factors
Given the right circumstances — a
transatlantic plane flight, a stretch of hot weather or a bout of punishing
exercise — anyone can become dehydrated. But certain people are at greater
risk, including:
| Infants and children. Worldwide,
dehydration secondary to diarrhea is the leading cause of death in children.
Infants and children are especially vulnerable because of their relatively
small body weights, low sweating capacity, and high turnover of water and
electrolytes. They're also the group most likely to experience diarrhea. In
the United States, diarrhea remains one of the most common pediatric
illnesses.
| Older adults. As you age, you become
more susceptible to dehydration for several reasons: Your body's ability to
conserve water is reduced, your thirst sense becomes less acute and you're
less able to respond to changes in temperature. What's more, older adults,
especially those in nursing homes or living alone, tend to eat less than
younger people do and sometimes may forget to eat or drink altogether.
Disability or outright neglect may also prevent them from being well
nourished. These problems are compounded by chronic illnesses such as
diabetes, by hormonal changes associated with menopause and by the use of
certain medications. The gravity of dehydration in seniors was brought home
in August 2003, when thousands of older adults in Europe died during an
unprecedented heat wave.
| Endurance athletes. Anyone who exercises
can become dehydrated, especially in hot, humid conditions or at high
altitudes. But athletes who train for and participate in ultra marathons,
triathlons, mountain climbing expeditions and cycling tournaments such as
the Tour de France are at particularly high risk. That's because the longer
you exercise, the more difficult it is to stay hydrated. During exercise,
your body can absorb about 24 to 32 ounces of water an hour, but you may
lose twice that amount in hot weather. With every hour, your fluid debt
increases. Dehydration is also cumulative over a period of days, which means
you can become dehydrated with even a moderate exercise routine if you don't
drink enough to replace what you lose on a daily basis.
| People with chronic illnesses. Having
uncontrolled or untreated diabetes puts you at high risk of dehydration. But
other chronic illnesses also make you more likely to become dehydrated.
These include kidney disease, cystic fibrosis, alcoholism and adrenal gland
disorders. Even having a cold or sore throat makes you more susceptible to
dehydration because you're less likely to feel like eating or drinking when
you're sick. A fever increases dehydration even more.
| People living at high altitudes. Living,
working and exercising at high altitudes — generally defined as 8,000 feet
to 12,000 feet (about 2,400 meters to 3,600 meters) — or very high
altitudes — 12,000 feet to 18,000 feet (about 3,600 meters to 5,400
meters) can cause a number of health problems. One is dehydration, which
commonly occurs when your body tries to adjust to high elevations through
increased urination and more rapid breathing — the faster you breathe to
maintain adequate oxygen levels in your blood, the more water vapor you
exhale. |
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When to seek
medical advice
If you're a healthy adult, you can usually
treat mild to moderate dehydration by drinking more fluids. Get immediate
medical care if you develop severe signs and symptoms such as extreme thirst, no
urination for eight hours, shriveled skin, dizziness and confusion.
Treat children and older adults with even
greater caution. Call your family doctor right away if your child:
| Develops severe diarrhea, with or
without vomiting or fever
| Has had episodes of vomiting for more
than 12 hours
| Has had moderate diarrhea for five days
or more
| Can't keep down fluids Is irritable and
much sleepier or less active than usual Has any of the signs or symptoms of
mild or moderate dehydration |
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Go to the nearest hospital emergency room
or call 911 if you think a child or older adult is severely dehydrated. You can
help prevent dehydration from becoming severe by carefully monitoring someone
who is sick and giving fluids at the first sign of diarrhea, vomiting or fever
and by encouraging children to drink plenty of water before, during and after
exercise.
Screening and
diagnosis
Your doctor can often diagnose dehydration
on the basis of physical symptoms such as little or no urination, sunken eyes
and skin that lacks its normal elasticity and resilience when pinched. If you're
dehydrated, you're also likely to have low blood pressure, especially when
moving from a prone to a standing position, a faster than normal heart rate and
reduced blood flow to your extremities.
To help confirm the diagnosis and pinpoint
the degree of dehydration, you may have other tests, such as:
| Blood tests. These may be used to check
your electrolytes, especially sodium and potassium; to look for signs of
concentrated blood; and to evaluate how well your kidneys are working.
| Urinanalysis. The color and clarity of
your urine, the presence of carbon compounds (ketones) and your urine's
specific gravity — that is, the mass of the urine as compared with equal
amounts of distilled water — all help show whether you're dehydrated and
to what degree. A high specific gravity, for example, indicates significant
dehydration. |
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If it's not obvious why you're dehydrated,
your doctor may order additional tests to check for diabetes and for liver or
kidney problems.
Complications
Hypovolemic shock is one of the most
serious complications of dehydration. It occurs when low blood volume causes a
drop in blood pressure and a corresponding reduction in the amount of oxygen
reaching your tissues. If untreated, severe hypovolemic shock can cause death in
a matter of minutes.
Other life-threatening complications
include:
| Swelling of the brain (cerebral edema).
Most often, the fluid you lose when you're dehydrated contains the same
amount of sodium your blood does (isotonic dehydration). In some instances,
though, you may lose more sodium than fluid (hypotonic dehydration). To
compensate for this loss, your body produces particles that pull water back
into the cells. As a result, your cells may absorb too much water during the
rehydration process, causing them to swell and rupture. The consequences are
especially grave when brain cells are affected.
| Seizures. These occur when the normal
electrical discharges in your brain become disorganized, leading to
involuntary muscle contractions and sometimes to a loss of consciousness.
| Kidney failure. This potentially
life-threatening problem occurs when your kidneys are no longer able to
remove excess fluids and waste from your blood.
| Coma and death. When not treated
promptly and appropriately, severe dehydration can be fatal. |
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Treatment
The only effective treatment for
dehydration is to replace lost fluids. The best way to do that depends on your
age, the severity of your dehydration and its cause.
Treating dehydration in sick children
Your doctor can offer specific suggestions for treating dehydration in your
child, but some general guidelines include the following:
| Use an oral rehydration solution. Unless
your doctor advises otherwise, use an oral rehydration solution such as
Pedialtyte or Ricelyte for infants and children who have diarrhea, vomiting
or fever. These solutions contain water and salts in specific proportions to
replenish both fluids and electrolytes. They also contain glucose or another
carbohydrate such as rice powder to enhance absorption in the intestinal
tract. Oral rehydration products are readily available in most drugstores,
and many pharmacies carry their own brands. The secret is to begin giving
fluids early in the course of an illness instead of waiting until the
situation becomes urgent.
In an emergency, or when traveling
abroad, you can make your own oral rehydration solution by mixing 1/2
teaspoon of salt, 1/2 teaspoon of baking soda and 3 tablespoons of sugar in
a quart of pure water. Be sure to measure accurately because incorrect
amounts can make the solution less effective or even harmful.
In most developing countries you also
can buy packets of a powdered oral rehydration solution, WHO-ORS, originally
developed by the World Health Organization to treat diarrhea and dehydration
in infants with cholera. Reconstitute the powder in bottled or boiled water
according to the directions on the package.
Whatever alternative you chose, be sure
to give enough solution. Your doctor may suggest specific amounts, depending
on your child's age and degree of dehydration, but a general rule of thumb
is to keep giving liquids slowly until your child's urine becomes
clear-colored. When your child is vomiting, try giving small amounts of
solution at frequent intervals — 1 teaspoon every minute, for instance. If
your child can't keep this down, wait 30 to 60 minutes and try again. Room
temperature fluids are best.
| Continue to breast-feed. Don't stop
breast-feeding when your baby is sick, but add an oral rehydration solution
as well. If you give your baby formula, try switching to one that's
lactose-free until diarrhea improves — lactose can make diarrhea worse.
Your doctor may also suggest substituting an oral rehydration solution for
the formula for 12 to 24 hours.
| Avoid certain foods and drinks. The best
liquid for a sick child is an oral rehydration solution — plain water
doesn't provide essential electrolytes, and although sports drinks replenish
electrolytes, they replace those lost through sweating, not through diarrhea
or vomiting. Avoid giving your child salty broths, milk — especially
boiled milk — sodas, fruit juices or gelatins, which don't relieve
dehydration and which may make symptoms worse. |
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Treating dehydration in sick adults
Most adults with mild to moderate dehydration from diarrhea, vomiting or fever
can improve their condition by drinking more water. The operative word is water.
Coffee, tea and other beverages that contain caffeine may temporarily increase
dehydration, and fruit juices and sodas can make diarrhea worse.
Treating dehydration in athletes of all
ages
For exercise-related dehydration, cool water is your best bet. There's no need
for salt tablets — too much salt can lead to hypernatremic dehydration, a
condition in which your body not only is short of water but also carries an
excess of sodium. Some people prefer sports drinks containing electrolytes and a
carbohydrate solution, but they're not essential unless you're exercising
strenuously for an hour or more.
Treating severe dehydration
Children and adults who are severely dehydrated should be treated in a hospital
emergency room where they can receive salts and fluids through a vein
(intravenously) rather than by mouth. Intravenous hydration provides the body
with water and essential nutrients much more quickly than oral solutions do —
something that's essential in life-threatening situations.
Prevention
Preventing dehydration sounds easy enough:
consume lots of fluids and foods high in water such as fruits and vegetables.
But questions as to how much fluid, what kind and when to drink muddy the
waters. Unfortunately, determining appropriate water intake isn't an exact
science, especially because so much depends on your age, physical condition,
activity level, locale and your own unique physiology.
Some general guidelines exist, however. The
most familiar is probably the 8 by 8 rule — that is, drink at least eight
8-ounce glasses of water a day. Though this recommendation isn't backed up by
much scientific evidence, it may work for you.
A better idea may be the replacement plan.
Most adults lose about 2.5 liters of water a day through breathing, sweating and
elimination. Food accounts for about 20 percent of your fluid intake, so
consuming 2 liters of water a day (a little more than 8 cups) in addition to
your normal diet should replace what you lose. On the other hand, the Institute
of Medicine recommends more — 13 cups of liquids a day for men and about 9
cups for women.
Perhaps the best overall recommendation is
to make a conscious effort to keep yourself hydrated and to make water your
beverage of choice. That might mean drinking water with every meal and between
each meal; taking water breaks instead of coffee or tea breaks; and substituting
sparkling water for alcohol.
These guidelines are rough estimates and
don't take into account special circumstances such as strenuous exercise, heat
and humidity, pregnancy, breast-feeding, and illness. In those cases, you may
need to drink much more.
| Exercise. In general, it's best to start
hydrating the day before strenuous exercise. Producing lots of clear, dilute
urine is a good indication that you're well hydrated. Two hours before an
endurance event such as a marathon or half-marathon, drink 2 cups of water.
One to 2 cups of water is usually adequate before shorter bouts of exercise.
During the activity, replenish fluids at regular intervals, and continue
drinking water or other fluids after you're finished.
Keep in mind that drinking too much can
not only cause bloating and discomfort, it may lead to a potentially fatal
condition in which your blood sodium becomes too low (hyponatremia). This
occurs when you drink more fluids than you lose through sweating.
| Environment. You need to drink
additional water in hot or humid weather to help lower your body temperature
and to replace what you lose through sweating. You may also need extra water
in cold weather if you sweat while wearing insulated clothing. Heated,
indoor air can cause your skin to lose moisture, increasing your daily fluid
requirements. And altitudes greater than 2,500 meters (8,200 feet) can also
affect how much water your body needs.
| Pregnancy or breast-feeding. Women who
are pregnant or breast-feeding need additional water to stay hydrated and to
replenish lost fluids. The Institute of Medicine recommends that pregnant
women drink 2.3 liters (nearly 10 cups) of liquids a day and that women who
breast-feed consume 3.1 liters (about 13 cups).
| Illness. Start giving extra water or an
oral rehydration solution at the first signs of illness — don't wait until
dehydration occurs. And although they might sound appealing, traditional
"clear fluids" such as ginger ale or other sodas contain too much
sugar and too little sodium to replenish lost electrolytes. |
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By Mayo
Clinic staff |
