We have been taught to drink a lot of water. Some people drink 64 fl oz. – or two liters — of water a day. Are eight 8 oz. glasses of water too much or just enough?
Our bodies need water and salt. If we drink too much water too rapidly we risk diluting our salt content and putting ourselves in a state of hyponatraemia — a loss of enough salt in the blood — and that can lead to heart trouble and brain malfunction.
Not even marathon runners are immune from drinking too much water during a race:
Dr Tunstall-Pedoe said: “One patient in the study estimated that he
drank approximately 13 litres during the five hours he took to complete
the marathon which is more than five times the recommended amount.
“Drinking excessively before during and after the event can be
Dr David Martin, an exercise psychologist from Georgia State
University, who studied joggers’ drinking habits believes people who
take up running for the first time are often advised to drink too much
London Marathon organisers advise slower runners, or those taking
longer than three hours 30 minutes to complete the course to drink no
more than half a litre of fluid per hour.
This advice is particularly relevant at colder temperatures.
Hyponatremia is entirely preventable, Dr. Adner and others
said. During intense exercise the kidneys cannot excrete excess water.
As people keep drinking, the extra water moves into their cells,
including brain cells. The engorged brain cells, with no room to
expand, press against the skull and can compress the brain stem, which
controls vital functions like breathing. The result can be fatal.
But the marathon runners were simply following what has long been the
conventional advice given to athletes: Avoid dehydration at all costs.
“Drink ahead of your thirst,” was the mantra.
Doctors and sports drink companies “made dehydration a medical illness
that was to be feared,” said Dr. Tim Noakes, a hyponatremia expert at
the University of Cape Town.
“Everyone becomes dehydrated when they race,” Dr. Noakes said. “But I
have not found one death in an athlete from dehydration in a
competitive race in the whole history of running. Not one. Not even a
case of illness.”
On the other hand, he said, he knows of people who have sickened and
died from drinking too much.
Now we know marathon runners need to be careful of their fluids intake,
but what about the rest of us?
Every day you lose water through your breath,
perspiration, urine and bowel movements. For your body to function
properly, you must replenish its water supply by consuming beverages
and foods that contain water.
A couple of approaches attempt to approximate water needs for the
average, healthy adult living in a temperate climate.
* Replacement approach. The average urine output for adults is 1.5
liters a day. You lose close to an additional liter of water a day
through breathing, sweating and bowel movements. Food usually accounts
for 20 percent of your total fluid intake, so if you consume 2 liters
of water or other beverages a day (a little more than 8 cups) along
with your normal diet, you will typically replace the lost fluids.
* Dietary recommendations. The Institute of Medicine advises that men
consume roughly 3.0 liters (about 13 cups) of total beverages a day and
women consume 2.2 liters (about 9 cups) of total beverages a day.
Even apart from the above approaches, it is generally the case that if
you drink enough fluid so that you rarely feel thirsty and produce
between one and two liters of colorless or slightly yellow urine a day,
your fluid intake is probably adequate.
CNN’s Paula Zahn revealed this in an interview:
ZAHN: … I try to get through six glasses right here
during the “American Morning” show. So I’ve been living in a state of
flotation for many years here, and now you say I didn’t need to do
this. What’s going on?
COHEN: Well, actually, before I tell you that, Paula, I have to ask
you, do you sweat a lot during the show?
COHEN: Never, then you don’t need all that much water.
ZAHN: … because they keep the air conditioning here at like 60
degrees to make sure everybody’s alert and thinking well.
COHEN: Right, exactly. Yes, it works, too, doesn’t it?
ZAHN: Yes, it does.
COHEN: Well, if you’re not sweating a lot during your show, then you
probably don’t need quite as much water as you think you do.
This eight eight-ounce glasses a day it turns out, after talking to the
USDA, the National Academy of Sciences, the National Institutes of
Health, people at various universities, they say, you know what, this
appears to be kind of a myth. We can’t find a single study that says
that that’s what people ought to do.
So I’m sitting next to a myth. Let’s show the myth that I’m sitting
next to. This is eight ounces — eight eight-ounce glasses of water.
This is, theoretically, according to the myth, what you’re supposed to
You can also look at it this way, that you’re supposed to
be drinking these two containers of water. All those people who are,
you know, being, I guess, nerds like you, Paula, and walking around
with those big bottles of water.
Snopes.com gets in on the over-watering action:
Kidney specialists do agree on one thing, however: that the
8-by-8 rule is a gross overestimate of any required minimum. To replace
daily losses of water, an average-sized adult with healthy kidneys
sitting in a temperate climate needs no more than one liter of fluid,
according to Jurgen Schnermann, a kidney physiologist at the National
Institutes of Health.
One liter is the equivalent of about four 8-ounce glasses.
most estimates, that’s roughly the amount of water most Americans get
in solid food. In short, though doctors don’t recommend it, many of us
could cover our bare-minimum daily water needs without drinking
anything during the day.
Too much water in the body messes up the body’s chemistry:
In a word, yes. Drinking too much water can lead to a
condition known as water intoxication and to a related problem
resulting from the dilution of sodium in the body, hyponatremia. Water
intoxication is most commonly seen in infants under six months of age
and sometimes in athletes.
A baby can get water intoxication as a
result of drinking several bottles of water a day or from drinking
infant formula that has been diluted too much. Athletes can also suffer
from water intoxication. Athletes sweat heavily, losing both water and
Here are some water myths:
In real life your body needing two to three litres a day
doesn’t mean endless glasses of water — in fact the food you eat
contributes about one litre to the total, and your body produces
another 250 mL when it uses the food, leaving you with only about
1.25-1.75 L to actually drink.
That’s only about five to seven large
glasses (each 250 mL or one cup).
And the really good news is that almost any fluid counts. Sometimes
it’s said that tea and coffee don’t because caffeine is a diuretic, but
in fact the evidence suggests that for tea and coffee at least, the
effect is only slight.
A review by an eminent US physiologist has put to rest many myths about
drinking enough water:
* Myth 1: By the time you get thirsty you’re already dehydrated. Not
true: you’ll feel thirsty before your body reaches a state that falls
into the category of dehydration.
* Myth 2: If your urine is dark, you’re dehydrated. In most instances
this doesn’t signal dehydration, though it does reflect a lower (but
probably normal) urinary volume.
* Myth 3: Lots of water keeps your kidneys’ filtering rate up. In fact,
the rate at which the kidneys filter is only reduced in very severe
dehydration — such as when you’ve already lost 5% of your body weight.
* Myth 4: You can’t drink too much water. Actually, you can.
You don’t have to be a marathon runner or an infant to be felled by water intoxication:
GEORGE NEGUS: We’ve had the “water and plenty of it”
lesson drummed into us for generations now. And that’s precisely why it
comes as a bit of a jolt to learn that too much fresh water can
actually be as damaging as dehydration. Doesn’t make sense? Here’s
Shelly Horton again in the Top End to convince us.
SHELLY HORTON: You can get it walkin’. You can get it talkin’. You can
get it herdin’ a cow. Matter of fact, I’ve got it now. A hard-earned
thirst deserves a good, cold…drink of water. Because water is the
best way to quench your thirst. It’s free, there’s no calories and it
doesn’t rot your teeth. But did you know that if you drink too much
water, it’s just as bad as not drinking enough? Environmental scientist
Georgia Miller nearly died because she drank too much water. Earlier
this year, she was doing fieldwork in the Northern Territory, and she
wasn’t used to the extreme heat and was worried about dehydration. So
she made sure she kept her water levels up.
GEORGIA MILLER: I was drinking up to about 10 litres, sometimes even 12
litres of water, a day. Keep in mind that I was pretty active,
physically active, during my work, and that I was spending a large
portion of each day outside in the heat, in full sun.
SHELLY HORTON: But Georgia didn’t realise how dangerous it is to
overhydrate the body. She soon started suffering the symptoms of
hyponatremia, or water intoxication.
GEORGIA MILLER: I started experiencing dizziness, nausea. I had a
couple of seizures, one of which lasted 15 minutes. Later that evening,
I went into a coma, which lasted for 1.5 days.
Moderation is everything. Your body should tell you when it needs
water. Listen to yourself when you speak. Remember there is no minimum
required intake of water a day.
If you are drinking a lot of water a day there could be other reasons
behind that thirst like diabetes.
Ask your doctor about your unquenchable thirst and see if your blood
and other body fluids are in the appropriate range of health.
There is no scientific study that commands we intoxicate ourselves on
64 fl oz. – or two liters — of water a day.