Caffeine and Dehydration

G. Douglas Andersen, DC, DACBSP, CCN

In my previous article, Caffeine and Athletic Performance three of the studies we reviewed also measured caffeine's effect on hydration. In each case, the conclusion was that caffeinated fluids did not cause greater fluid loss through sweat or urine than non-caffeinated beverages.1, 2, 3

Survey your family, friends, patients or colleagues to see who believes caffeinated beverages cause bathroom trips. Most people consider it a fact that caffeine dehydrates. Ask them what school they learned this in and you'll get a puzzled look followed by an answer such as, "I didn't learn it in school. I learned it when I started drinking coffee." This entrenched belief causes a dilemma among athletes looking for an edge. On one hand, a growing number are aware (via popular press and internet) of the growing body of evidence that caffeine improves performance. Conversely, (depending on the degree) athletes know dehydration not only harms performance, it can stop it.

This month we will review a unique study on caffeine and dehydration.4 Unlike most studies on this topic, this was not a done over a few hours. Fifty-nine men (average age 21) were studied over a 13-day period. The protocol was as follows:

  1. Prior to the intervention no caffeine was consumed for 48 hours.
  2. On days 1 through 6, all subjects ingested 3 milligrams per kilogram of body weight (mg/kg/bw) prior to performing their normal workouts in a variety of sports.
  3. On days 7 to 11, the subjects were divided into three blinded groups. They were either given a zero caffeine placebo (Group1), 3 mg/kg/bw (Group 2), or 6 mg/kg/bw (Group 3). The mean level of caffeine ingested was 226 mg for the 3 mg/kg/bw group, and 452 mg for those who took 6 mg/kg/bw.
  4. Blood and urine were tested on days one, three, six, nine and twelve.

Table 1
Urinary Excretion with Different Levels of Caffeine:
Group 1 Group 2 Group 3
Day Caffeine
1 0 1465 0 1484 0 1593
3 3 1626 3 1587 3 1487
6 3 1605 3 1347 3 1641
9 0 1303 3 1636 6 1446
12 0 1410 3 1371 6 1349

By reading the results in Table 1, it is clear that in this study caffeine ingested up to 6 mg/kg/bw [~ 450mg for a 165 pound person] did not have a diuretic effect or cause dehydration. Add the evidence from other recent trials1,2,3 we reviewed last month and one can safely say caffeine in doses less than 500 mg will not cause fluid loss during vigorous activity.

So what about the evidence that supports caffeine's effect as a diuretic? We will address that issue next month.

1Chen, S.C., Davis, J.M., Mattews, E., et al. Effects of Caffeinated Sports Drinks on Physical/Mental Function During Team Sports Exercise. Medicine and Science in Sports and Exercise Med Sci Exerc 2007;39(5):S43, A-700.
2Strecker, E., Foster, E.B., Taylor, K., et al. The Effect of Caffeine Ingestion on Tennis Skill, Performance and Hydration Status. Medicine and Science in Sports and Exercise Med Sci Exerc 2007;39(5):S100, A-953.
3Trilik, J.L., Millard-Scafford, M.L., Cureton, K.J., et al. Hydration During Exercise in Warm Humid Conditions: Effect of a Caffeinated Sports Drink. Medicine and Science in Sports and Exercise Med Sci Exerc 2007;39(5):S100, A-954.
4 Armstrong, L.E., Pumerantz, A. C., Roti, M.W., et al. Fluids, Electrolytes, and Real Indices of Hydration During 11 Days of Controlled Caffeine Consumption. Int J Sport Nut Exerc Met. 2005;15(3):252-65.


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