Coffee has a chemical complexity that, through the roasting process, creates a broad range of vibrant flavor characteristics. This same molecular diversity is also responsible for a variety of health effects in humans. Caffeine is certainly the most well-studied, but it is far from the only pharmacologically active molecule extracted during a brew. Some of these chemicals are elusive, and their effects poorly understood. Others, after decades of research, have concrete benefits and detriments firmly borne out by data.
In this 8-part blog series, we delve into the myriad truths, half-truths, and indeed, fallacies, related to the impact that coffee has on your health. Is it good for you? Is it bad for you? Is it going to make your teeth brown? Does coffee make you smarter? Read on to find out.
Part 2: Hydration & Sports
The Hydration Myth:
Chances are you’ve heard well-meaning family and friends tell you you’re going to get dehydrated if you drink coffee. Maybe you’ve passed on that advice yourself. In fact, the dehydrating effect of coffee is one of the most persistent food myths out there - a pound of exaggeration that comes with an ounce of truth.
Caffeine, pharmaceutically, falls into a class of natural stimulants called methylxanthines. In fact, it does exert an effect on hydration. During blood filtration the kidneys are responsible for removing waste and excess water and re-absorbing nutrients that may still be of use. Caffeine causes the body to eliminate more salt, and with salt goes water. In theory, you would produce more urine drinking coffee than if you were to drink a glass of water.
While the mechanism of action in the body certainly suggests truth to the dehydration talk, the problem is in the dose. In healthy adults, a dose of 4mg/kg body weight caffeine, or about 2-3 cups a day, will cause no clinically recognizable change in hydration status versus consuming the same amount of water. Any mild dehydration effects noted at these consumption levels are seen in ‘caffeine-naive’ individuals: non-caffeine drinkers on the occasion that they have a cup of coffee. The rest of us build and maintain a tolerance very quickly.
These results are validated in study after study after study. Yet the dehydration myth persists- to the point that healthy average coffee consumers receive recommendations to lay off the caffeine to improve their hydration. Even in the event that you consumed truly herculean doses of coffee the amount of water lost through the diuretic effect of caffeine would be dwarfed by the amount of water consumed with the coffee. To put it briefly, it’s not a concern.
Coffee and Exercise:
So if coffee doesn’t cause dehydration, should you be drinking before or during vigorous exercise? Studies on caffeinated versus decaffeinated sports drinks have shown that caffeine does not adversely affect body temperature regulation or hydration status, even with strenuous exercise in warm, humid conditions.
In fact, many top olympians use coffee to boost athletic performance, some claiming that it has the greatest beneficial effect of any legal substance. These effects are attributed to coffee’s ability to increase the speed of signal transmission throughout nerve tissues, as well as its tendency to suppress pain.
The effect has been studied repeatedly in top athletes with the greatest performance improvements seen in endurance athletes. That dose of caffeine is between 3 to 7 mg/kg body weight and the science suggests drinking your fill thirty minutes to an hour before you need it to kick in. To put the level of improvement into perspective a University of Georgia study found a 24% increase in endurance performance for athletes consuming coffee at this level before exercise.
If you want to figure out approximately how many 8 oz cups are right for you you can use this formula.
(Your weight in lbs. X 3 mg caffeine per kg) / (95 mg caffeine in a cup X 2.2 lbs per kg) = number of 8 oz. cups
This formula gives the low end of coffee consumption according to these studies. For the high end you can just double it, but remember that these are 8 ounce cups, which are not the same as the ones you might be making or buying. On top of that, not every cup of coffee has 95 mg caffeine. It's best to be conservative and add more joe as needed.
It is worth noting also that you should know your own response to coffee before incorporating it into a vigorous workout. As noted in Part 1 of this series, for some individuals coffee can be a gastric irritant or even have a laxative effect. Barring individual reactions however, the evidence would suggest that athletes can make greater gains in performance with the aid of coffee than without.
Perrier E, Vergne S, Klein A, Poupin M, Rondeau P, et al. (2013) Hydration biomarkers in free-living adults with different levels of habitual fluid consumption. Br J Nutr 109: 1678–1687
Maughan R, Griffin J. (2003) Caffeine ingestion and fluid balance: a review. J Hum Nutr Diet 16(6): 411-20.
Eddy N, Downs A. Tolerance and cross-tolerance in the human subject to the diuretic effect of caffeine, theobromine, and theophylline. (1928) J of Pharm and Exp Therapeutics 33(2): 167-174.
Killer S, Blannin A, Jeukendrup A. (2014) No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One 9(1).
Millard-Stafford M, Cureton K, Wingo J, Trilk J, Warren G, Buyckx M. (2007) Hydration during exercise in warm, humid conditions: effect of caffeinated sports drinks. Int J Sport Nutr Exerc Metab 17(2): 163-177.
Grandjean A, Reimers K, Bannick K, Haven M. (2000) J of the Amer Col of Nutr 19(5): 591-600.
Armstrong L, Pumerantz A, Roti M, Judelson D, Watson G, et al. (2005) Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption. Int J Sport Nutr Exerc Metab 15(3): 252-265.
Erickson A. (2017) Science just debunked a coffee myth that’s been around since 1928. Readers Digest. http://www.rd.com/health/wellness/is-coffee-a-diuretic/
Aubrey, A. (2014) Coffee myth-busting: cup of joe may help hydration and memory. NPR. http://www.npr.org/sections/thesalt/2014/01/13/262175623/coffee-myth-busting-cup-of-joe-may-help-hydration-and-memory
Perez-Lopez A, Salinero J, Abian-Vicen J, Valades D, Lara B, et al. (2015) Caffeinated energy drinks improve volleyball performance in elite female players. Med Sci Sports Exerc 47(4): 850-6.
Christensen P, Peterson M, Friss S, Bangsbo J. (2014) Caffeine, but not bicarbonate, improves 6 min maximal performance in elite rowers. Appl Physiol Nutr Metab 39(9): 1058-63.
Glaister M, Pattison J, Muniz-Pumares D, Patterson S, Foley P. (2015) Effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance. J Strength Cond Res 29(1): 165-74.
Higgins S, Straight C, Lewis R. (2016) The effects of preexercise caffeinated coffee ingestion on endurance performance. Int J Sport Nutr Exerc Metab. 26(1): 221-39.
Carpenter M. (2014) How athletes strategically use caffeine. The Atlantic. https://www.theatlantic.com/health/archive/2014/03/how-athletes-strategically-use-caffeine/283758/
Hobson, K. (2014) Caffeine gives athletes an edge, but don’t overdo it. NPR. http://www.npr.org/sections/health-shots/2014/08/01/336886286/caffeine-gives-athletes-an-edge-but-dont-overdo-it