Caffeine, Fluid-Electrolyte Balance, Temperature Regulation, and Exercise-Heat Tolerance

Lawrence E. Armstrong; Douglas J. Casa; Carl M. Maresh; Matthew S. Ganio

Disclosures

Exerc Sport Sci Rev. 2007;35(3):135-140. 

In This Article

Electrolyte Balance

Table 2 compares the urinary excretion of sodium (Na+) and potassium (K+) while consuming either caffeine or a control (i.e., one fluid or total diet); eleven distinct experimental treatments (8 studies) are depicted. A large range of Na+ and K+ losses occurred (columns 2 and 3); this range likely stems from the varied electrolyte contents of the fluid consumed by the subjects (column 1).

A greater (P < 0.05) acute natriuresis (column 2) was reported after caffeine intake in 7 of 9 acute experiments (duration of 2-4 h). This is consistent with the physiological action of caffeine, inhibiting reabsorption of sodium (Na+) at renal nephrons. However, the lone chronic study (6 or 11 d of controlled caffeine intake) reported no statistical differences between 0-, 226-, and 452-mg conditions in 24-h pooled urine collections.[3] As with acute urinary water loss, Na+ excretion may increase acutely when caffeine is consumed, but daily Na+ balance is positive; this indicates that human Na+ regulatory mechanisms successfully defend whole-body exchangeable Na+.

Regarding K+ excretion ( Table 2 ), the data in column 3 suggest that kaluresis is similar in virtually all water and caffeine trials. One investigation[3] controlled dietary caffeine intake at 452 mg·d-1 for six consecutive days. The 19 subjects exhibited a mean 24-h K+ excretion (column 3) that was within 2% of the mean level of 20 subjects who consumed 0 mg of caffeine.

The adequate intake value published by the National Academy of Sciences of the United States is 204 mEq Na+ per day, for male and female subjects older than 14 y.[23] Thus, an adequate diet provides ample sodium to cover the urinary losses reported in Table 2 (125 or 140 mEq·d-1). Also, the 24-h K+ losses after caffeine intake (column 3) are similar to the adequate intake value for K+.[23] Thus, the available research on Na+ and K+ excretion does not support abstaining from or reducing dietary intake of caffeine.

Interestingly, the studies conducted by González-Alonso et al.[14] and Brouns et al.[5] indicate that electrolyte losses are acutely reduced when caffeine is consumed in a fluid that contains electrolytes and carbohydrates during a 2-h postexercise recovery period. Although not significantly different, a trend existed in 3 of 4 experiments ( Table 2 , columns 2 and 3) for the total urinary Na+ and K+ losses to be greater during water trials. This possibility deserves further research and may involve reduced glomerular filtration during exercise.

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