New study suggests coffee is not dehydrating after all

I am a regular coffee drinker. In fact, I honestly cannot remember the last time I went a day without coffee. I have loved the taste of coffee since childhood, and I expect I do get something from the caffeine too. I appreciate that coffee-drinking does not have a particularly healthy reputation, though there is at least some evidence which links coffee consumption with improved health outcomes, including a reduced risk of type 2 diabetes. While these ‘epidemiological’ studies do not prove that coffee drinking is healthy (they only show that coffee-drinking is associated with improved outcomes), coffee is rich in ‘antioxidant’ substances (for example, polyphenols) that, at least in theory, might have disease-protective effects.

One common belief about coffee is that it dehydrates the body. Caffeine can act as a diuretic stimulate urine production). I, personally, have never worried about this because (even though I say so myself) my hydration status is usually good. I am pretty good about drinking water, and usually will drink enough to ensure that my urine remains yellow throughout the course of the day. In my head, I reason that as long as I ‘balance’ coffee with water, then dehydration is not a particular risk.

A study just out suggests that habitual coffee drinkers have little to worry about regarding the potential dehydrating effects of coffee. In this study, 50 men who are regular coffee-consumers ate and drank a controlled diet for three days on two occasions. On one occasion, the prescribed diet was supplemented with four, 200 ml glasses of water each day. On the other occasion, this was replaced with four, 200 ml cups of coffee, containing a total of 4 mg of caffeine per kg of body weight. The total amount of caffeine consumed was about 320 mg per day for each man (about the same amount of caffeine that would be found in four cups of instant coffee).

The men underwent a range of tests before and after each 3-day spell, including markers of hydration in the blood and urine and urine volume. The results were essentially the same, which led the authors to conclude that hydration status was unaffected by moderate coffee and caffeine consumption compared with water. In other words, in these men, coffee was essentially as hydrating as water. This is generally good news for regular coffee-consumers like me.


1. Killer SC, et al. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS ONE 2014;9(1):e84154

10 Responses to New study suggests coffee is not dehydrating after all

  1. Arthur Taylor 20 January 2014 at 4:00 pm #

    Hmm! – nobody else here like coffee then? Although I’ve never been too bothered by it’s bad press amongst health fanatics, it’s nice to have it exonerated on this property. Slightly OT, my elderly stomach doesn’t like alcohol so I drink very little of it nowadays and don’t get too upset about it, but I’d be seriously bothered if I couldn’t have my morning coffee binge!

  2. bill 21 January 2014 at 7:50 pm #

    Dr Briffa:

    Your readers come from all around the world. Surely some of them would be interested in our nutrition conference here in San Luis Obispo, California on March 1st, 2014.

    Here’s the link to the conference information:

    We are having some excellent presenters:

    Eric Westman, MD
    Jay Wortman, MD
    Steve Phinney, MD, PhD
    Jeff Volek, PhD, RD
    Lynne Daniel Ivey

    We hope many of your readers are interested. Thanks.

  3. Tom 24 January 2014 at 3:01 pm #

    I also tend to drink a lot of coffee throughout the day. I enjoy the taste and the effects of the caffeine.

    I seem to be very good at conserving fluid; I drink relatively little (other than coffee!), and tend to have fairly concentrated urine. But my body seems to function well like this; I very rarely get headaches, and if I am made to feel guilty by some colleague or magazine article about my low water intake and drink just a few extra glasses of water throughout the day, all that happens is I very quickly need to go to the loo, and I pass very dilute urine! I can’t help but feel that this extra fluid has done nothing for me; if I was constantly dehydrated, surely my body would just relish the extra fluid and put it to good use?

    I seem to remember Dr Davis at Heartscanblog saying something about people with a particular phenotype; “the perfect carnivore” – Lp(a) gene carriers. They respond well to high fat, low carbohydrate diets, they have efficient metabolisms and so quickly put on weight with even moderate carbohydrate intake, but tolerate prolonged fasts and low water intake extremely well.

    These people also tend to be above average intelligence… well, it’s not for me to say!

  4. William L. Wilson, M.D. 24 January 2014 at 9:30 pm #

    John–A minor correction. You state: “I am pretty good about drinking water, and usually will drink enough to ensure that my urine remains yellow throughout the course of the day.” I suspect that the more water you drink, the less yellow your urine will be.

    I too am a coffeholic. Since my college cramming days I have consumed at least 8-10 cups of coffee a day will no obvious ill effects. Caffeine is a brain-enhancing substance and with me 12 hour work days I need all the enhancement I can get!

  5. Jack 25 January 2014 at 12:21 am #

    I thought healthy urine should be almost colourless; the darker yellow the more dehydrated one is?
    I drink 3-4 espressos a day and feel I couldn’t live without it. However, I use a Nespresso machine & worry that the aluminium in the coffee pod lids will give me Alzheimer’s. Any helpful thoughts on that would be most welcome.

  6. Cee WB 25 January 2014 at 7:44 am #

    I too was a coffeeholic, I got through 6 or so coffees a day but about two weeks I dropped it down to 1 to 2 a day and feel so much better, I was feeling bloated and fatigued and thought I’d just see if the coffee was simply too much after a pretty long life (pretty aged now) and it’s been an amazing result. I feel so much better now.

  7. Sallie 25 January 2014 at 1:43 pm #

    I find instant coffee a bit more digestable, especially in the morning, than the usual brew.. A friend that is very health- conscious says instant coffee is very bad. is it?

  8. Margo 25 January 2014 at 3:34 pm #

    We buy 50-50 coffee, half decaffeinated, often known as New York Blend. We like the taste, and don’t worry about too much caffeine.

  9. Rita 22 August 2014 at 12:58 pm #

    Dr. Briffa, I know you don’t usually comment on readers’ comments unless there’s a controversy to which you must respond. Therefore, this is in the form of a question about coffee that I hope you will address in some way at some point.

    I too love my coffee and find it a delightful way to start the day. I drink just one cup, because I’m so sensitive to caffeine. I don’t notice that it does me any harm and I feel it does me some good, at the very least in terms of pleasure. Still, I often read in articles about diet and health that one must eliminate coffee in order to correct numerous diseases and conditions, as if there were something inherently unhealthy about coffee.

    What’s the real deal here, Doctor?


  1. New study suggests coffee is not dehydrating after all « wchildblog - 19 January 2014

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