To what extent does coffee drinking cause dehydration, as if often
alleged?  If this is a real effect, what's the cause?  If it's the
caffeine, does decaffinated coffee cause the same problems?

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Request for Question Clarification by tehuti-ga on 12 Nov 2002 19:13 PST

I found only four studies in the medical literature that deal
specifically with this topic.  One study showed that coffee did
increase urination and decreased hydration.  This had the subjects
drinking quite a large amount of coffee: 6 cups.  I then found three
further studies which looked at beverages containing caffeine, rather
than coffee itself, and found no significant effect of caffeine on
fluid balance. If this will suffice, I can post details of these
studies as an answer.

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Clarification of Question by michael2-ga on 12 Nov 2002 23:02 PST

Yes, details of those studies would be fine.

I was quite astonished at first sight when I did this research, as I
knew that coffee has a diuretic effect.
Several sources with new studies negate this:

"Q2: Is coffee or caffeine dehydrating? 
A: There is no evidence that consumption of any caffeinated beverage
causes a fluid-electrolyte imbalance that is detrimental to health or
exercise performance. A review of recent studies on caffeine and
dehydration concluded that the caffeine consumed in 1 to 4 cups of
coffee a day does not increase dehydration. (37)."
from:
Other questions about coffee
( http://www.coffeescience.org/other.html )

On the other side "Online Health" says:
"Caffeine and alcohol act as diuretics, further increasing your water
needs."
and on the caffeine content of coffee:
"Coffee, brewed - 40 to 180mg per cup
Coffee, instant - 30 to 120mg per cup
Coffee, decaffeinated - 3 to 5mg per cup"
from:
( http://www.digitalnaturopath.com/cond/C569985.html )

Well - what do you do when the experts are not of the same opinion ? I
ask a good encyclopedia and the best one I know is the Encyclopedia
Britannica:
"Caffeine has a stimulating effect on the central nervous system,
heart, blood vessels, and kidneys. It also acts as a mild diuretic"
from: Encyclopedia Britannica CD ROM Deluxe Edn. 2001

Thatīs the solution, maybe: they say itīs a mild diuretic.

And itīs clear that it is the caffeine that causes the diuretic
effect. So drinking decaffeinated coffee will definitely reduce the
effect.

The questions about the mechanism:
"The exact mechanisms which lead to this diuretic effect are not
known"
form: 
Nutriquest
( http://www.nutrition.cornell.edu/nutriquest/coffee.html )


Search Strategy:
( ://www.google.de/search?sourceid=navclient&hl=de&q=coffee+dehydration+mechanism
)
and
( ://www.google.de/search?sourceid=navclient&hl=de&q=caffeine+diuretic+mechanism
)
and the CD ROM Ed. 2001 of the Britannica


till-ga

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Request for Answer Clarification by michael2-ga on 07 Nov 2002 13:12 PST

I agree that the result of the June 2002 research mentioned in the
first of your links is surprising.  But I seriously doubt that the
best way to resolve conflicting conflicting points of evidence, one of
which comes from a paper that was not published until 2002, is to look
at an enyclopaedia that was published in 2001.

Your second link simply says - without quoting any evidence at all -
that 'Dehydration may result from the increased urinary frequency
brought on by caffeine'.  How reliable do you consider that to be?  As
reliable as the research?  More? Less?

Doesn't that statement simply _assume_ that caffeine causes
dehydration, which is pretty similar to the very thing I stated in the
question as being 'often alleged'?  I know it's often alleged.  I want
to know if it's true.

I rather feel that so far you've not really analyed my question at
all, but instead done a quick search and posted a couple of links that
happened to come up.  Using the internet as a search tool doesn't
absolve a reseacher from the normal requirement of critical thought.

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Clarification of Answer by till-ga on 07 Nov 2002 15:25 PST

a)
"But I seriously doubt that the best way to resolve conflicting 
points of evidence, one of which comes from a paper that was not
published until 2002, is to look at an encyclopaedia that was
published in 2001."

I canīt really follow this point of view. Encyclopedias represent a
kind of basic knowledge that is looked upon as true by many experts.
The German Brockhaus Encyclopedia for example is considered as
evidence at court in Germany. Iīm sure that one can rely on such basic
knowledge.


b)
"Your second link simply says - without quoting any evidence at all -
that 'Dehydration may result from the increased urinary frequency
brought on by caffeine'."

Sorry, but again Iīve got some problems to follow your arguments. The
quote IS considered as evidence. What kind of evidence do you expect ?
 I found several sources and they all said that itīs the caffeine that
causes the dehydration.
Which is in perfect concordance with the quote from Britannica. 

c)
"I want to know if it's true."

Yes, it is true. Most of the sources you can find (and there are many
sources) state that coffee/caffeine  causes dehydration.

d)
"Using the internet as a search tool doesn't absolve a researcher from
the normal requirement of critical thought."

In contrast to your assumption I must say that I visited a lot of
websites, not just the two websites I quoted. And I do read the
material in a critical way.
 

Please keep in mind that researchers are not experts with a scientific
background in all the fields they research. I am however a chemist and
I remember that in my organic chemistry studies the dehydrating effect
of caffeine was mentioned.
By the way: a lot of people drinking coffee (including myself) will
agree that they made the experience that there is as a matter of fact
a dehydrating effect.

A last remark:
When you read the article quoted in the first link you will see:
"While there have been several studies done that show caffeine is a
mild diuretic, there is no evidence that exercise, when combined with
the consumption of caffeine or caffeinated beverages, will result in
chronic dehydration, and this is contrary to the advice of most
exercise physiologists, physicians and dietitians,” explains
Armstrong, who has conducted fluid balance research since 1980."
from:
( http://ific.org/proactive/newsroom/release.vtml?id=20842 )
So what they are talking about is that caffeine does not cause
"chronic dehydration". Maybe that was the point that confused us.


till-ga

I have never before had to request a refund but I am afraid I am less
than happy with this researcher's methodology.  Of the two links
provided, one simply re-phrases a generally-held opinion that I
mentioned in my original question, whereas the second (citing a some
June 2002 research) was illogically rejected as wrong by the
researcher on the basis of an encyclopaedia article that was written
long before the research came out.  My comments in the Request for
Clarification still stand, and it appears that the researcher simply
hasn't understood where he or she gone wrong.

I'd like this to be re-posted for one of your other excellent
researchers to have a go at.

Hello michael2-ga,

The overall consensus of published studies in the medical literature
is that drinking coffee, whether caffeinated or not, and other
caffeinated beverages will not have a significant dehydrating effect,
if any at all. One study did indicate that mild dehydration may be
experienced with high coffee consumption.

My search strategy was to search the bibliographical database Medline
at Pubmed on the web site of the National Library of Medicine
(http://www.ncbi.nlm.nih.gov/entrez/query.fcgi)  As search terms I
used “coffee”, “caffeine”, “caffeic acid” and “chlorogenic acid” (two
other major constituents of coffee), and combined each of them with
the terms “dehydration”, “hydration”, “fluid”, “diuretic”.  I did a
separate search for each pair of terms.  I was surprised to find very
few studies that had the specific objective of researching the effects
of coffee/caffeine on fluid balance and hydration. I first summarize
my findings overall, and then list the articles I found below,
together with my own summary of each one and a URL to the more
extensive Medline summary (in one case to the full text) of the
article.

Firstly, coffee can have a diuretic effect and reducing caffeine
intake was found to decrease urinary frequency, urgency and leakage in
people with urinary symptoms (see ref. 6).  However, whether the
diuresis caused by coffee leads to dehydration is another question.  A
study (see ref 1) of volunteers given 6 cups of coffee found that they
did show a average decrease in total body water of 2.6%.  Therefore a
relatively high level of coffee consumption may cause a mild degree of
dehydration.  However, another study (see ref 4) found that drinking
various combinations of water and caffeinated and non-caffeinated
beverages gave “no significant differences in the effect of various
combinations of beverages on hydration status of healthy adult males”.
 A review of the literature on the effects of caffeine on athletic
performance concluded “There is no evidence that caffeine ingestion
before exercise leads to dehydration, ion imbalance, or any other
adverse effects.” (see ref 3).  Another review (ref 2, with which you
are already familiar), looked at 10 published studies, which
investigated caffeine doses of 100-680 mg, concluded that caffeine is
mildly diuretic, but not more so than water. Caffeine was not found to
be associated with significant levels of dehydration, and any
dehydrating effects it did have were smaller in people who had
developed tolerance through regular consumption.  One further
interesting fact is that the diuretic effect of caffeine was found to
be lower in conditions of physical exercise than at rest (see ref 5). 
The authors suggested that the diuretic effect of caffeine might be
counteracted by the increase in levels of plasma cathecholamines
(norepinephrine, adrenalin, dopamine) during exercise. Similarly to
the studies quoted so far, the authors concluded concluded that
caffeine consumed in sports drinks “during moderate endurance exercise
apparently does not compromise bodily hydration status.”
One last piece of circumstantial evidence comes from a study into the
prevention and treatment of urinary stones (see ref 7). Maintaining
adequate hydration is a key element in prevention. The authors found
“Hydration has proved effective …  …"fluids" may consist of water (any
kind), coffee (caffeinated or decaffeinated), tea, beer and wine”,
thus providing further indirect confirmation that coffee does not
markedly affect hydration.
The studies I found pertained only to coffee and caffeine.  Therefore,
the other major constituents of coffee, chlorogenic acid and caffeic
acid, do not seem to have a role in the effects of coffee on hydration
status.

1. Annals of Nutrition and Metabolism 1997; Vol. 41(no. 1):29-36 
Coffee consumption and total body water homeostasis as measured by
fluid balance and bioelectrical impedance analysis.
Neuhauser-Berthold, Beine S, Verwied SC, Luhrmann PM.
Institute of Nutritional Sciences, Justus Liebig University, Giessen,
Germany.

The authors put 12 healthy volunteers onto a standardized diet in
which mineral water was the only liquid. On the 6th day, they replaced
some of the water with 6 cups of coffee containing 642 mg caffeine.
The result was an increase in the amount of urine excreted over 24
hours.  The average increase was 753 ml (+/- 532 ml).  At the same
time, there was a decrease in body weight and total body water was
found to have decreased by an average of 2.7%.   This study therefore
shows that a relatively high level of coffee consumption does lead to
a degree of dehydration.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9194998&dopt=Abstract

2.  International Journal of Sport Nutrition, Exercise and Metabolism
2002 Jun; Vol 12 (no. 2):189-206
Caffeine, body fluid-electrolyte balance, and exercise performance.
Armstrong LE.
Departments of Kinesiology, Nutritional Sciences, and Physiology &
Neurobiology, University of Connecticut, Storrs, CT 06269-1110, USA.

The author reviewed 10 published studies to find whether caffeine can
cause dehydration. The overall consensus from the studies is that
caffeine is mildly diuretic, but only to a similar extent to the
diuretic effect of water. The studies, which compared the effects of
100-680 mg caffeine with those of water or placebo seldom found a
statistically significant effect of caffeine on the volume of excreted
urine, and did not associate caffeine with a physiologically
significant level of dehydration. It also appeared that individuals
who have developed a tolerance to caffeine through regular consumption
are less likely to show any effects of caffeine on body hydration. 
The author concluded that moderate consumption of caffeince will not
adverely affect the fluid-electrolyte balance of athletes and other
sports enthusiasts, while people whose lifestyles are more sedentary
will have an even smaller risk because they lose less fluid through
sweating than athletes.

members of the general public should be a less risk than athletes
because their fluid losses via sweating are smaller.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12187618&dopt=Abstract

3. Sports Medicine 2001; Vol 31 (no. 11):785-807 
Caffeine and exercise: metabolism, endurance and performance.
Graham TE.
Human Biology and Nutritional Sciences, University of Guelph, Ontario,
Canada.

This is another review of the literature on the effects of caffeine on
athletic performance. The author concludes “There is no evidence that
caffeine ingestion before exercise leads to dehydration, ion
imbalance, or any other adverse effects.”
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11583104&dopt=Abstract


4. Journal of the American College of Nutrition, Vol. 19, No. 5,
591-600 (2000)
The Effect of Caffeinated, Non-Caffeinated, Caloric and Non-Caloric
Beverages on Hydration
Ann C. Grandjean, EdD, FACN, CNS, Kristin J. Reimers, RD, MS, Karen E.
Bannick, MA and Mary C. Haven, MS
The Center for Human Nutrition, (A.C.G., K.J.R.), Omaha, Nebraska
School of Allied Health Professions, University of Nebraska Medical
Center (M.C.H.), Omaha, Nebraska
Bannick Consulting, Isle, Minnesota (K.E.B.) 

This was a study in 18 healthy males aged 24-39. They were made to
drink various combinations of water and caffeinated and
non-caffeinated beverages.  The authors concluded “This preliminary
study found no significant differences in the effect of various
combinations of beverages on hydration status of healthy adult males.
Advising people to disregard caffeinated beverages as part of the
daily fluid intake is not substantiated by the results of this study.”
Full text at: http://www.jacn.org/cgi/content/full/19/5/591

5. International  Journal of Sports Medicine 1997 Jan; Vol. 18 (no
1):40-46
Caffeine vs caffeine-free sports drinks: effects on urine production
at rest and during prolonged exercise.
Wemple RD, Lamb DR, McKeever KH.
Exercise Physiology Laboratory, Ohio State University, Columbus, USA.

The authors compared the effects of caffeinated and non-caffeinated
sports drinks on urine production and water balance during rest and
during exercise. They did find a statistically significant difference
in the amount of urine produced at rest, with greater quantities being
produced after consumption of caffeine. However, there was no
significant difference between the two groups during exercise. The
authors suggest that the diuretic effect of caffeine might be
counteracted during exercise by the increased levels of plasma
catecholamines (norepinephrine, adrenalin, dopamine) that result from
physical activity.  They conclude caffeine consumed in sports drinks
“during moderate endurance exercise apparently does not compromise
bodily hydration status.”
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9059904&dopt=Abstract


6. British Journal of Nursing 2002 Apr 25-May 8; Vol.11(no 8):560-565
Caffeine reduction education to improve urinary symptoms.
Bryant CM, Dowell CJ, Fairbrother G.
Prince Henry and Prince of Wales Hospitals, Australia.
The objective of this study was to see whether reducing caffeine
consumption would have an effect in 95 patients with urinary symptoms.
 They found that reducing caffeine intake did reduce urinary
frequency, urgency and leakage.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11979209&dopt=Abstract

7. Journal of Nephrology 2000 Nov-Dec; Vol. 13 Supplement 3: S65-70 
Medical prevention and treatment of urinary stones.
Colussi G, De Ferrari ME, Brunati C, Civati G.
Niguarda-Ca' Granda Hospital, Milan, Italy. 

The authors review strategies for the prevention and treatment of
urinary stones. Adequate hydration is one of the key elements of
prevention.  “Hydration has proved effective in clinical trials and
population-based observational studies; "fluids" may consist of water
(any kind), coffee (caffeinated or decaffeinated), tea, beer and wine;
grapefruit juice appears to have an unexplained ill effect.” This is
therefore indirect evidence that coffee, whether caffeinated or
decaffeinated, does not affect the maintenance of optimal levels of
hydration.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11132035&dopt=Abstract

This definitely falls into the 'Great Answer' category!  Excellent service.

If you drink coffee, that contains caffeine, your frequency of
urination will increase.  If you don't compensate this loss in fluid
by drinking more water, you will become dehydrated.  One of the
consequences of dehydration is the disturbance of the electrolyte
balance of the blood.

From this disturbance, all other pathologies associated with
dehydration will result.  Even if you drink decaffinated coffee, you
will still be drinking coffee that contains caeffine, although a
relatively low level. The same types of physiological events occur
when you drink caeffinated soft drinks.

So, in a nutshell, watchout for what you drink and drink in
moderation.

Just my opinion. The human body uses lots of water (ammong other
stratagies) to flush out poisons such as caffeine. The result is an
occassional short fall of water for a wide variety of other purposes,
so the water is obtained from tissues, which can spare some water
without serious damage. Most food and beverages (including
decaffeinated coffee) have other poisons besides caffeine, so doing
controlled experiments with humans is difficult, resulting in
contridicty conclusions especially when the resarch if financed by a
group with strong finacial interest in the outcome.   Neil