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    Myth: Coffee Consumption Leads To Dehydration
    By News Staff | January 9th 2014 05:35 PM | 6 comments | Print | E-mail | Track Comments

    Because caffeine is a mild diuretic, there is a common assumption that caffeinated beverages, such as coffee, also have this effect.

    The problem is that a kernel of scientific knowledge can be misconstrued in news outlets. As we discussed on Thanksgiving, everything in a Thanksgiving dinner contains chemicals found by someone somewhere to be a carcinogen in rats and could therefore be banned if they did not occur naturally. 

    The dose matters, though telling that to people who insist they are allergic to genetically modified corn is probably a waste of time. Conflating pure caffeine with coffee is also difficult but if a researcher wants to find something, they can. Impartial investigations about the effects of caffeine in the form of coffee on hydration status have been inconclusive. 

    A new paper finds no evidence for a link between coffee consumption and dehydration - at least when it comes to normal coffee consumption. Coffee is mostly water so a moderate amount of coffee not only doesn't result in dehydration,  it contributes to daily fluid requirements just as other fluids do. 


    Mean total body water estimates from Day 1–Day 3. n = 25. 
    doi:10.1371/journal.pone.0084154


    The authors say this is the first study to directly assess the effects of coffee consumption compared to equal volumes of water. Sophie Killer, a  University of Birmingham School of Sport and Exercise Sciences researcher and lead author of the study commented, "Despite a lack of scientific evidence, it is a common belief that coffee consumption can lead to dehydration and should be avoided, or reduced, in order to maintain a healthy fluid balance. Our research aimed to establish if regular coffee consumption, under normal living conditions, is detrimental to the drinker's hydration status."

    In a sample of regular coffee drinkers, the authors measured the effects of moderate consumption of black coffee compared to the consumption of equal volumes of water on fluid balance and hydration status. Fifty male participants were tested in two phases, where they were required to drink four mugs (200ml) of either black coffee or water per day for three days. In the second phase, those who had initially drunk coffee switched to water and vice versa.

    The two phases were separated by a ten day 'wash out' period. Females were excluded from the trial to control against possible fluctuations in fluid balance resulting from menstrual cycles.

    To assess hydration status, the researchers used a variety of well-established hydration measures including body mass and total body water, as well as blood and urine analyses. The researchers found no significant differences in total body water or any of the blood measures of hydration status between those who drank coffee and those who drank water. Furthermore, no differences in 24-hour urine volume or urine concentration were observed between the two groups.

    "We found that consumption of a moderate intake of coffee, four cups per day, in regular coffee drinking males, caused no significant differences across a wide range of hydration indicators compared to the consumption of equal amounts of water," said Killer. "We conclude that advice provided in the public health domain, regarding coffee and dehydration, should be updated to reflect these findings."


    Citation: Killer SC, Blannin AK, Jeukendrup AE (2014) No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population. PLoS ONE 9(1): e84154. doi:10.1371/journal.pone.0084154

    Comments

    My apologies if I don't agree with this. As a moderate coffee drinker, (3 cups a day) I find I produce much more fluid after drinking coffee than the amount of coffee I'm drinking. I know this because I've recently had to record output for medical testing of non-dehydration related kidney stones. What I do find interesting is how these coffee stories always appear right after a downtrend in coffee sales is identified.

    Hank
    It was 50 people so obviously plenty were just like you, as the chart shows. But there are going to be variations in individuals. Aspirin doesn't help all people either but that doesn't mean aspirin doesn't work.

    However, implying that studies are done as PR for products is not warranted. For one thing, it fails the obvious logic test of all unsubstantiated conspiracies, in that too many people would know. Secondly, you have no evidence to libel their ethics. Finally, this has to have been written last year, and last year, even in a terrible US economy, coffee sales were up to $11.7 billion - an increase of 11.4% from 2012. Any industry in the world wishes they had that growth so coffee sales are not down.
    JohnK.
    As a prodigious (1 pot a day) coffee drinker I can say I have never seen any difference.  More than once this topic been brought up.  From my perspective there is no difference between coffee and drinking a pill containing the same quantity of caffeine. 

    Odds are good that drinking a pot of water has more to do with any consequences than the caffeine pill that I took with it.
     


    I tend to followup the copious amounts of coffee with copious amounts of beer though. How does that interfere?

    PLOS is a peer-reviewed journal....  Do most of the peers also receive money from the coffee industry?  By reading the study (which I did), it was obvious the researchers had already decided what kind of a result they wanted to find!

    Based on the source of their funding, the researchers had set up the research study to reduce the concerns about dehydration.    
    "Furthermore, if participants felt they were not allocated a sufficient volume of water at any point during the first trial or indeed if they had too much water, they were permitted to return to the laboratory to have their fluid allocation amended. "

    Feel parched?  Come to the lab, and we will give you more water! End of research period, nobody appears dehydrated!  Conclusion = Coffee does not make you dehydrated!

    WHAT KIND OF A SCIENTIFIC STUDY (for dehydration) IS THIS?

    BOGUS, fake, spurious, false, fraudulent, sham, deceptive; counterfeit, forged, feigned; make-believe, dummy, pseudo, phony, pretend, fictitious.(any more synonyms?)  

    It is shoddy research practices and shoddy reporting like Jenn Harris' which promotes politicians to reduce funding for real research!

    Hank
     By reading the study (which I did), it was obvious the researchers had already decided what kind of a result they wanted to find!
    There are zero science studies done that don't start with a hypothesis. And common hypotheses are often common beliefs. Alleging it is a Big Coffee conspiracy and they simply picked a group, wrote a check and these people produced the result dictated by Big Coffee is conspiratorial crackpottery. You know nothing about science when you mischaracterize even the basics without even thinking first.