Friday Weird Science: Why does coffee make you pee?

Mar 26 2010 Published by under Friday Weird Science

Last week during Weird Science, Sci got to hear a lot more about people's urine odors than she probably ever REALLY wanted to know.
But hey, why be shy?
And so you may imagine that urine and fluids have been on Sci's mind a little bit lately. Another thing has also been on Sci's mind: the sheer amount of coffee that she has been drinking.
coffee-shaking.jpg
She may be actually jonesing for her late PM dose right about now...
Sci has heard from many quarters that Coffee makes you pee, and that this is because caffeine is a diuretic. On the other hand, Sci has also heard that coffee only makes you pee because it's a liquid and you're drinking it, rather than any specific diuretic properties. So which is it?
This question is of great concern to Sci for several reasons. First, Sci drinks a lot of coffee. Second, Sci is a distance runner, and likes to compete in races. She's been reading a lot lately about how caffeine just before a workout or race is good, and can increase your performance. However, IF caffeine is ALSO a diuretic, this is something to keep in mind, because there is NOTHING worse than getting halfway through a 30K (18.5 miles, so say you're 9 miles in or so), and realizing that you REALLY have to pee (well, ok, maybe realizing you have diarrhea, or are going to vomit, pass out, or have a heart attack). Races always talk about having port-o-johns, but at the side of the trail? HAHAHAHAHAHA. No. Sci doesn't mind peeing in the woods, of course, but it wastes some seriously valuable time, especially in the shorter races, when a 30 second bathroom break WILL kill your chances of a win.
And so, Sci was curious, diuretic or not? She decided to take a look around.
ResearchBlogging.org Maughan and Griffin. "Caffeine ingestion and fluid balance: a review" Journal of Human Nutrition and Dietetics, 2003.
Riesenhuber et al. "Diuretic potential of energy drinks." Amino Acids. 2006.
Armstrong et al. "Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption." Int J Sport Nutr Exerc Metab. 2005.
Eeek! Hold on, pee break!
*flush*
*phew*


All right let's go.
So it turns out (according to this review) that caffeine is indeed a diuretic, meaning that it causes you to expel more urine than the amount of water contained in the drink of choice. So people have become concerned that if you drink caffeinated beverages, you might lose too much water. This probably wouldn't affect a healthy person at all, but some groups like the elderly might suffer larger effects, or effects that might interact with other drugs they are taking (if, for example, you were on another diuretic like furosemide, which is prescribed sometimes for things like high blood pressure or heart failure, and, in the immortal words of one of my pharmacology profs "could make a brick pee". You don't want to be peeing anymore than you already are).
Luckily, there have been lots of studies looking at the effects of caffeine on urinary output and fluid balance (and a bunch of them have this person "L Armstrong" on them. I wonder if you are named "L Armstrong", you feel forced into studying exercise physiology. No matter what, it's a pretty awesome coincidence). The effects appear to vary by dose, but overall it looks like this:
If you're taking small amounts of caffeine (one study looked at 3mg, which is very small indeed), there's no diuretic effect, you pee as you normally would. If you're taking larger amounts, however (like this sports drink study that looked at sports drinks with 240 mg of caffeine), there IS a diuretic effect. In the review of the effects, it looks like the cutoff point is 250mg. Lower than that, no diuresis. Higher than that, you're peein' more than usual.
So you're probably asking, how much caffeine IS that? And for this, Sci has made you a picture. Sci doesn't have photoshop, but she did her best! Also, keep in mind that these are averages. Sci found several values for each drink recorded in several places, and got three data points that way so I could get averages with error bars. So is this scientific? HECK NO. Take with a grain of salt. You've been warned.
caffeine graph.jpg
So that's what it looks like. Coffee tops off the usual suspects with between 115-175 mg of caffeine per serving (**this is NOT Starbucks. I looked up Starbucks and they say their caffeine levels are 330 mg in a Grande 16 oz. Ouch.). Lower down you get things like energy drinks and sodas, and the lowest on the list is green tea (white tea may be lower). Highest up there was the highest caffeine level I could find, which was 500 mg in that 5150 thing. Sci finds it scary.
So it seems that, to get a high enough dose of caffeine to get a diuretic effect, you'd need 2-3 cups of regular drip coffee, or one cup of Starbucks. Chose your poison. Drinks like Coca cola and tea are probably going to be too low (though with serving sizes these days Sci isn't betting on it).
But the effect apparently doesn't stay with you. You can quickly develop tolerance to the diuretic effects of caffeine. So if you drink 2-3 cups of coffee daily (or more *cough cough* Sci *cough cough*), you will probably grow tolerant to the effects, and not pee as much as someone who just got dosed for the first time.
So how does it work?
What makes caffeine a diuretic? Well...Sci doesn't actually know, but she bets SOMEONE does!
Chemically, caffeine is a xanthine, which is a class of chemicals that increases the glomerular filtration rate (via the inhibition of sodium reabsorption, so more sodium returns to the blood, and water follows it. When this is blocked, sodium stays in the fluid that will eventually become the urine, and so the water stays there, too, this mechanism is SO fascinating and Sci really wishes someone would write some basic blog stuff on it, but not me because Sci is not an expert), which is how fast your kidneys can filter your blood, increasing the production of urine. Sci isn't entirely sure how it does this, but is pretty sure it has something to do with the fact that caffeine is an antagonist at adenosine receptors, meaning that it BLOCKS the effects of adenosine. In the brain, this results in increases in mental alertness, in the body this results in vasoconstriction and increases in blood pressure, and in the kidney...well, Sci isn't sure. My hypothesis would be that adenosine in the kidney acts to promote sodium reabsorption and that this is blocked by caffeine, but I'm not sure. Anyone out there know? I tried my pubmed-fu and couldn't find anything, but I'm probably overlooking something.
So anyway, it appears that caffeine, in high enough amounts, does indeed make you pee, but that people will grow tolerant to these effects fairly quickly. So if you plan on using it for races, and you're not taking too much, or make sure you're used to the effects, you should be fine (though one should ALWAYS go to the bathroom before races, just in case). So if you're used to your usual three cups a day, you probably don't have to worry, but if you're new to high caffeine intake, make sure you're near a port-o-john!
Maughan RJ, & Griffin J (2003). Caffeine ingestion and fluid balance: a review. Journal of human nutrition and dietetics : the official journal of the British Dietetic Association, 16 (6), 411-20 PMID: 19774754
Riesenhuber A, Boehm M, Posch M, & Aufricht C (2006). Diuretic potential of energy drinks. Amino acids, 31 (1), 81-3 PMID: 16847703
Armstrong LE, Pumerantz AC, Roti MW, Judelson DA, Watson G, Dias JC, Sokmen B, Casa DJ, Maresh CM, Lieberman H, & Kellogg M (2005). Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption. International journal of sport nutrition and exercise metabolism, 15 (3), 252-65 PMID: 16131696

38 responses so far

  • Fargo says:

    I've largely given up caffeine, having only the odd diet coke during the last two+ years, but a couple weeks ago I accepted a cup of coffee from one of my friends. I have no idea what grind, blend, or preparation method she uses, but she's Serious about coffee. It was like someone shot me with a methamphetamine dart.
    Anyway, anecdote aside I'd be curious to see a study on people that have become caffeine tolerant in regards to whether going off caffeine reduces urine output to below normal (I suppose you'd first have to establish what normal is) as the body adjusts to missing it's little helper.

  • Raptor says:

    I've always had a problem with caffeine, it gives me migraines. Until, I figured out that my migraines were not being caused by the caffeine, but instead because I was being dehydrated. I mean, I was having sweet tea with most of my meals and given the levels I was probably consuming and the fact I wasn't drinking any water.. well, it only took a few days of doing this (and peeing like a bloody race horse every 30 min) and then that migraine would hit. Now, I don't drink the stuff at all, and if I do, I only have a glass and very rarely. I still end up going pee more than usual if I do have a glass, but not that much. And it's probably more the fact I also have started drinking water with my tea, just because migraines are something I want to avoid. Still, would be interesting to see what levels of caffeine it would take me, someone who pretty much hasn't drinking caffeine for about 3 years now, to have the same effect as the people in the study. How long does the tolerance last, once you stop drinking it?

    • Brian says:

      Caffeine doesn't give you migraines. In fact, caffeine is a key ingredient in most (if not all) migraine medications. I'm not disputing your claim to getting headaches after taking in caffeine, but I'd be willing to bet a substantial amount that they are not migraine headaches.

      • Josh says:

        Caffeine makes you dehydrated and the cause of 99% of headaches is dehydration. This is the cause of her headaches not the actual caffeine, but the results on her body (i.e. dehydration) that cause the headaches.

      • gloria says:

        He did say it was from being dehydrated from the caffeine. Which is solid truth. I have a book cald what u don't know maybe killing u. U should always flush out caffeine with water. U will still get the wired effect just flush out the salt collection. But yes caffeine also helps headaches also.

      • Aref says:

        Caffeine is a drug- stimulant. When one takes more than 600mg of caffeine a day it results in caffeinism. Withdrawl Symptoms include insomnia, restlessness, excitement, tachycardia (irregular heartbeat), hand tremors, difficulty concentrating, severe headaches, increase in urrination, and tinnutis.

        The reason why most people get headaches is because of their addiction from caffeine. When the withdrawal or intake of the drug stops, they get a headache. If you get headaches from withdrawal of caffeine and take medication for margrains your relaspsing and fulfilling your crave for caffeine.

  • Travis says:

    Should I be concerned that I laughed a little at 2 or 3 cups of coffee? Two or three cups is perhaps my starting point, often only part of my morning because I have been known to have quite a few more. I have a few more during the day and maybe a couple of cups of tea as well.
    I swear I am not addicted, I totally went off it one summer. But I haven't slept in a few years.

  • chezjake says:

    It's been a while since I took pharmacology (back in 1962, when Goodman and Gilman was still published on clay tablets), but then again, the xanthine alkaloids were in medical use for a long time before that. So, a couple points that come to mind.
    1. I was taught that there is more individual variation in the pharmacological responses to caffeine than there is to any other known drug. (Perhaps Abel at Terra Sig can provide more up-to-date info.) Most of us are aware that some people become absolutely hyper and wired on one cup of coffee while others can guzzle it right up to bedtime and still sleep like babies. Thus, I would tend to be dubious of studies on caffeine that do not have a very large n for subjects, and even then I'd want to see those lovely error bars.
    2. People should not be misled by the lowly position of tea on Sci's graph. Yes, tea is relatively low in caffeine, but it's significantly higher in theophylline (another xanthine alkaloid), and way back when theophylline was actually marketed as a diuretic.
    3. When considering the effects of caffeine on frequency of urination in runners or other athletes, I'd also want to see some exercise physiology/pharmacology that takes into account the loss of fluids through perspiration and any effects that has on frequency of urination. (Back in my own days as a miler, I'd seldom need to urinate for several hours after a race, no matter how much Coke, iced tea, or coffee I drank.)

  • steffi suhr says:

    Going to the potty halfway during my first marathon made me finish in just over four hours. There was a queue! Not sure whether this was because of my caffeine intake though - I also chuckled at your two to three cups a day... I must have developed a serious tolerance over the years.

  • Ian Tindale says:

    Obviously the “two to three cups per day” statement was an error, clearly it should have read “two to three cups per hour”, but if we accept that mistake, it’s also worth considering how much sugar a person takes in after a day’s worth of coffees (obviously coffee can’t be consumed without sugar — it tastes vile like that, it’s got coffee in, after all).

  • Jesse says:

    I beg to differ, Ian. Coffee is only at its best without sugar.
    I started with milk and sugar. Sometimes I'd add some Swiss Miss (you know, instant, water-based hot chocolate).
    Over the years (I started coffee when I was maybe 15, 16) I have moved off it. Now I take it black, no sugar. My parents do too, or they throw in some milk occasionally. (But I think that's to cool it down).
    Anyhow, I brew it in a percolator at low heat on the stove. Takes a mite longer but it really, to my mind, works better-- also controlling for grind. When you grind too finely it isn't as good.
    My worst period: Japan. There is no good coffee there. It's all instant. That's vile. Britain was better, these days (I lived there some years back) and I credit all the Jamaicans in the country with introducing really good stuff.
    And the Philippines is an underrated coffee producer. Had some brought back by the wife's family. Lovely stuff.
    I liken coffee to red wines. You have to get bast the fact that it isn't sweet and let it sit on the tongue for a moment, and enjoy the aroma. Really.
    I am way too enamored of this, huh?

  • plutosdad says:

    So you are comparing 6-8 oz of drip coffee to 16 oz of Starbucks and saying Starbucks has double? For a "Science" blog I'm pretty shocked you paid no attention to what the actual size of the portion is so that we are comparing apples to apples. At least you mentioned it was the 16 to clue us in.
    A 5 second google search brought accoridng to the American Beverage Association, 8oz of coffee has anywhere between 104 to 192 mg, which puts SBUX and other "strong" expensive brands right in line with regular old joe.
    Also red bull has 80mg, but many other energy drinks have a lot more.
    I used to take coffee before a long run, at least a half hour before, not because I wanted to pee but to clear out the other pipes. It worked. If the writer was dedicated enough to run pro (I assume since she wants to win) she wouldn't be stopping to elminate: as you run just let it flow free!
    The interesting thing is even decaffienated will help clear out the other pipes, but i've never read research on whether that's psychosomatic or there is some other chemical doing it.

  • Dr Becca says:

    Jesse, you are just enamored enough! I go nuts for coffee. Am about to consume a 32 oz french press over the course of the next 2 hrs or so.
    Black-no-sugar is the only way; if you need to add anything to your coffee, you're probably not drinking good enough coffee. I might forgive you if you're a supertaster (perhaps a FWS-worthy phenomenon, Sci!)
    Sci, don't the diuretic effects of caffeine come from that it's a vasopressin inhibitor? It kind of sounds like that's what your describing without actually saying "vasopressin," but I just wanted to check! That's always been my understanding.

  • LGRooney says:

    @ plutosdad, #8,
    I have noticed that the morning cup (equivalent to about three espressos) does a marvelous job of cleaning out the "other" pipes. I reckon it is a function of the temperature. Try drinking cool coffee in the morning and see whether it has the same effect. My own experimentation with this, i.e., I have poured leftover coffee into a cup when late to bed so I didn't have to brew anything fresh in the morning and waste time and I didn't have the same "urgency." When it is fresh and hot, though, it is rather quick in pushing through. Therefore, I have concluded that gulping large amounts of hot brew tends to shock the stomach into action. Better yet, pour a glass of ice water at the same time as you pour your hot coffee an chase one with the other. Your stomach will probably revolt at the sight of the temperature contrast.
    @Fargo, #1, I have the opposite problem when going off coffee. If I haven't had a cup in a while, my head is so ridiculously pounding and pained that I have to chase the aspirin with volumes of water that send me off to pee (problematic because it is easy to miss while standing with one's head in hands or in complete darkness to avoid the light piercing every pore in my skull).
    Or is that TMI for everyone?

  • Skas says:

    @ #8
    For a "Science" blog I'm pretty shocked you paid no attention to what the actual size of the portion is so that we are comparing apples to apples.
    I'm pretty shocked that a "science" blog reader demonstrates poor reading comprehension. Or is it just selectively ignore sentences that would weaken an already bizarre insult?

    Sci found several values for each drink recorded in several places, and got three data points that way so I could get averages with error bars. So is this scientific? HECK NO. Take with a grain of salt. You've been warned.

    N.O.-xplode is a pre-workout supplement a surprising number of friends and coworkers use. A single scoop contains about 100mg of caffeine (listed as methylxanthine). Of course this is just one of a very long list of ingredients, some seem arbitrary and others probably pointless. No idea about the interactions with other additives.

  • Scicurious says:

    plustosdad: A fair point about Starbucks, Sci obviously hadn't had her evening cup of coffee. Thanks for pointing it out. And Sci is not yet dedicated enough to let it flow free...maybe once she's doing marathons. Finishing in just OVER 4 hours due to a pee break would break Sci's little heart.
    As for the cleaning out other pipes, caffeine DOES serve as a muscle relaxant in the bowel. So that's probably why people have noticed this effect.
    LRGooney: your withdrawal headache is VERY common, caffeine is a vasoconstrictor, and it's thought (at least, the last time I looked we thought, which was a while ago) that the vasodilation you get in caffeine withdrawal contributes to the headache.
    And yeah, Sci LOLd at the 2-3 cups per day, too! I think we are all sufficiently tolerant to the effects...
    Jesse: there IS no "too enamored" of a good coffee. Sci has her own grinder and is the biggest coffee snob in her laboratory. It pains her inside when they all insist on drinking the Dunkin' Donuts blend instead of my locally roasted micro-blends.

  • jolly says:

    Dr.Becca, as a supertaster, one sip of coffee is so ugly that I can't do it. But I absolutely love the smell of coffee. I wish I could drink coffee and I have friends that have beautiful rituals around it and another friend that has a business roasting coffee.

  • Ewan says:

    32oz in 2h, Becca? That sounds about right :).
    The secret* - which I learned from an old Spider Robinson novel, but which seems to be coming into more common awareness - to coffee excellence is a dash of salt. Try it: makes an enormous difference, attenuating any bitterness, rounding the flavour profile, and accentuating nuttiness. For me, it negates the need to add e.g. sugar.
    [*OK, _one_ of the many secrets. And not actually a secret. Pfui.]

  • I feel in good company here! I just came from a blog where the question of the day was: What beverage do you drink? Out of at least 50 respondents, I was the only one who drank coffee all day!
    Sure, I am tolerant enough to pee normally, but I'm dependent on caffeine. Years ago, someone at work made a pot of decaf because we were out of regular coffee and didn't tell me. I developed the worst headache of my life.

  • Pascale says:

    Love the urinefest! Keep the golden prose flowing, please.

  • Epicanis says:

    Ah, interesting - Back in 2008 when I dug through pubmed on this I came firmly to the conclusion that the diuretic thing was just a vile slander against Our Friend, 1,3,7-trimethylxanthine. I don't think any of the studies I looked at were administering over 300mg/subject, though.
    I wonder if anyone's ever gotten around to trying to correlate possible diuretic effects to the actual level of caffeine and/or its metabolites in the bloodstream over time (which I gather can be quite variable from person to person) rather than flat single dosage?
    Thanks for this new information!

  • Anodyne says:

    Okay, so this is sort of OT, but I can't find information about it *anywhere*--
    I can drink a regular cup off coffee and doze off to sleep as if nothing was consumed. A lot of the time I actually get tired from drinking coffee (though strangely espresso rarely has this effect.)
    On the other hand, when I have, say, a Monster "energy shooter" with a similar amount of caffeine along with several other ingredients (glucose, L-Carnitine, inosotol, guarana, glucuronolactone, and maltodextrin plus inactive ingredients), I get the desired effect of alertness, etc.
    It doesn't really matter which energy drink it is; they all work to keep me awake. But the coffee makes me want to pass out at my desk. I still get jittery from it, but I have trouble staying awake at times despite that effect. I've even been known to sleep after two decent sized cups of java.
    Has anyone heard of this? Could there be another chemical in the coffee that causes the somnolence? Or does anyone know where to find any literature?
    Judging by the signals my bladder is currently sending, I surprisingly don't have enough tolerance for caffeine, despite consuming it often... *wanders to the restroom and grumbles about diuretics*

  • Donna B. says:

    I've been known to drive long distances across some of the western U.S. and found out a long time ago that caffeine tablets would help keep me awake without frequent pee stops.
    There are places in the U.S. where a female really doesn't want to pee. These include places where cactus grows, scorpions and rattlesnakes live, and some of the sketchier lesser known non-national-chain truck stops.

  • Donald Oats says:

    Concentrated caffeine, rather than a big watery coffee, is probably the way to go if you want a last minute hit of "alertness" before a big long run. I'd recommend a couple of doppio's (double short black). This is based upon the totally unscientific principle that if you knock back a lot of fluid before a race, you'll find it hard not to think about the potential need to pee, and guess what? Brain-body feedback makes it a self-fulfilling prophecy.
    On a more serious note, I used to feel the need to pee more often if I had coffee(s) during the day. Then I started taking pregabalin (aka lyrica, a gabapentoid) for severe chronic central neuropathic pain, dosing 600mg/day. It now appears that I can knock back as much coffee as I can handle without it increasing the need to pee. Basic softdrinks however do increase the need, if I have a couple of cans in an hour or two. I wonder whether gabapentoids in some way interfere with the diuretic effect of a large slug of Starbucks?

  • Left Coast Bernard says:

    "Chemically, caffeine is a xanthine, which is a" phyto-chemical!
    It is a chemical that comes from a plant!
    It is entirely natural!
    How can anyone imagine that it might have any bad effects?
    If something is a phyto-chemical, then it only has good effects. Everyone knows this, and it's taught on all the health food sites.
    If caffeine increases urination, then that must be a good and natural effect.
    If caffeine does not increase urination, then that must be a good and natural effect.
    If caffeine were to decrease urination, then that must be a good and natural effect.
    So what is this discussion about anyway?

  • otopsi says:

    It doesn't really matter which energy drink it is; they all work to keep me awake. But the coffee makes me want to pass out at my desk. I still get jittery from it, but I have trouble staying awake at times despite that effect.

  • Who's Yer Daddy? says:

    Well, any level of caffeine seems to have a diuretic effect on me; however, I can drink a green tea at 9:00 at night and still sleep just fine, whereas if I drink a 12-16 ounce Coke or iced tea at dinner, I will be awake until 1:00 AM and sleep only fitfully after that...

  • [...] your mood.  While it may give you a temporary lift, it also can make you a nervous wreck who pees every ten minutes (coffee is a diuretic) and overeats her way to obesity (coffee consumption is associated with [...]

  • Tsj says:

    I have been drinking coffee since I was 14 ( a little over 20 years). Since it was a strong believe back then that coffee is bad for kids. The 2-3 cups a day must be an error indeed. I used to drink between 12 and 15 mugs per working day (14 hours) back when I was a chef. Whenever I was off and slept in I used to get headaches the size of Russia, so I figured out that I was probably physically addicted to caffeine. I slowed down a little and that went away. Now I drink about 8-10 cups a day and I have a normal bathroom frequency and no withdrawal symptoms anymore. I think tolerance sets in quite quickly.

    @LG Rooney: My own experimentation with this, i.e., I have poured leftover coffee into a cup when late to bed so I didn't have to brew anything fresh in the morning and waste time and I didn't have the same "urgency."
    What? Are you serious? That must taste like heated up motoroil?

    I am by no means a Barrista or a connoisseur, but that just sounds wrong.
    Even though I live in England now, I still drink Dutch filter coffee, because the stuff they have here ( mostly instant) is horrible, unless you spend a fortune.

    P.S. Black, one sugar. preferably brown, cane sugar.

  • [...] your mood.  While it may give you a temporary lift, it also can make you a nervous wreck who pees every ten minutes (coffee is a diuretic) and overeats her way to obesity (coffee consumption is associated with [...]

  • evelyn says:

    hi, just to answer the blogger's question about the way that coffee increases urine output: well as you said caffeine increases blood pressure and in turn prevents nacl reabsorption and increases glomelular filtration. how does it do this? well if the bp is increased so is the rate at which blood is entering the kidneys and is being filtered. it also decreases nacl reabsorption because once the bp increases, a hormone is released from the atria of the heart called Atrial natriuretic peptide and it acts to lower bp. it does this by stimulating the release of renin- an enzyme that blocks release of aldosterone- which is a hormone that releases k+ into the collecing duct of the nephron and causes nacl to diffuse back into the blood as water follows. once this hormone is blocked nacl reabsoprtion is decreased and urine output increases. ANP also inhibits the release of ACTH hormone from the anterior pituitary. this hormone stimulates the rerlease of another hormone known as anti diuretic hormone. this hormone also increases the reabsorption of nacl and water by increasing the permeability of the loop of henle to nacl.

  • kira says:

    What? I get a diuretic effect from just ONE cup.

  • davey says:

    I don't drink any coffee most of the time (used to but not for years now). This week we accidentally acquired a box of Tim Horton's caffeinated (instead of decaf) and being frugal I insisted on drinking at least 4 cups of it over about 4 days. I have been peeing like crazy the past few days. It just started out of nowhere...I go and then 10 mins later I have to go again. I didn't even have any coffee yesterday (gonna throw out the rest of it) and I'm still peeing frequently. Tim's seems very very rich and strong, so I suspect that the info on their website of one small cup having only 80 mg of caffeine isn't accurate. I used to buy the Tim's canned for a coffee maker and according to the directions it said use 10 scoops per pot. When I did, people were choking on the stuff it was so strong. I got down to using 6 or even less scoops because of the richness of it. I would think there was a good 150 mgs in each cup, easy. I can't remember exactly how many cups I've had since Monday but I've had at least one every day starting Monday night but I skipped yesterday. So 4, maybe 5. That's a huge hit for me as I usually only drink water. And also I stopped drinking water while having the coffee so I am probably screwing up my whole system. Going to get back to my water.

  • Acid-freak says:

    I think the acidity of the coffee may make a difference in irritating the bladder (I know that highly acidic drinks like powdered lemonade, Coke, and coffee make me pee like crazy). I try reducing the acid by adding eggshells to the grind (a recipe that even my mother thought was old fashioned) or taking a calcium pill, with limited results. Maybe I'll try salt. I really like coffee but hate the diuretic effect and have to skip it before any athletic event--never mind just races. So far, I have yet to build up this "tolerance" you folks talk about.

    • Kait says:

      I love you. You just basically summarised 3/4 of an entire postgraduate semester there. You should totally write a book - 'nephrology for time poor students'. It is worth mentioning also that the initial filtration of the blood before it goes into the tubules for the 'fine tuning' that you have described so very superbly, is a gross filtrate. in other words much of what is initially filtered out is reansorbed according to the bodies need at that moment. It's always going to be either sodium or potassium that is released into urine or absorbed back into the blood, as they work on an either-or exchange. Which one totally depends on what the blood pressure is doing right then.
      Sci's article and your summary are super interesting to me and I'm wondering how much the potassium up (sodium down) that occurs in diuresis as with coffee influences the increased heart rate that coffee causes?

  • Brian Haden says:

    Hi! Great post and I think I may be able to help with why caffeine is a diuretic. Because caffeine is a vasoconstrictor and thus increases blood pressure, it drives glomerular filtration to a higher rate because the main force behind glomerular filtration rate is blood pressure! The body is awesome in it's simplicity sometimes. We just got done studying the nephron (where the glomerulus hangs out) and I found it fascinating.

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