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.
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.
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!
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.
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