Caffeine effects on urine production at rest and during prolonged exercise

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=9059904&dopt=citation

Wemple RD, Lamb DR, McKeever KH.

Exercise Physiology Laboratory, Ohio State University, Columbus, USA.

We compared the effects of caffeinated vs non-caffeinated carbohydrate electrolyte (CE) drinks on urine volume (UV), free water clearance (CH2O), fractional excretion of water (FEH2O), and osmolar excretion during 4 h of rest or 1 h rest followed by 3 h of cycling at 60% VO2max in six subjects. We also tested maximal performance at 85% VO2max following the 3-h exercise trials. Throughout the two resting trials and the two rest + exercise trials, subjects ingested CE (total volume = 35 ml/kg) without (PLAC) or with (CAFF) caffeine (25 mg/dl). Blood samples were collected, and body weight and UV were recorded every hour. Urine and blood were analyzed for osmolality and creatinine, and plasma catecholamine concentrations were determined. At rest, mean (+/-SE) UV between 60 min and 240 min was greater for CAFF (1843 +/- 166 ml) vs PLAC (1411 +/- 181 ml) (p < 0.01); during exercise the difference in UV between CAFF (398 +/- 32 ml) and PLAC (490 +/- 57 ml) was not significant. Cycling performance was unaffected by caffeine. Plasma catecholamine concentrations were not different between PLAC and CAFF but were greater during exercise than rest (p < 0.01) and may have counteracted the diuretic effect of caffeine observed at rest. Thus, CAFF consumed in CE during moderate endurance exercise apparently does not compromise bodily hydration status.
American College of Sports Medicine position stand Exercise and fluid replacement

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9303999&query_hl=15

Med Sci Sports Exerc. 1996 Jan;28(1):i-vii.


Convertino VA, Armstrong LE, Coyle EF, Mack GW, Sawka MN, Senay LC Jr, Sherman WM.

It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition: 1) It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-hr period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition. 2) It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water. 3) During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated. 4) It is recommended that ingested fluids be cooler than ambient temperature [between 15 degrees and 22 degrees C (59 degrees and 72 degrees F])] and flavored to enhance palatability and promote fluid replacement. Fluids should be readily available and served in containers that allow adequate volumes to be ingested with ease and with minimal interruption of exercise. 5) Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration greater than 1 h since it does not significantly impair water delivery to the body and may enhance performance. During exercise lasting less than 1 h, there is little evidence of physiological or physical performance differences between consuming a carbohydrate-electrolyte drink and plain water. 6) During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30-60 g.h(-1) to maintain oxidation of carbohydrates and delay fatigue. This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml.h(-1) of solutions containing 4%-8% carbohydrates (g.100 ml(-1)). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin). 7) Inclusion of sodium (0.5-0.7 g.1(-1) of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in n oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.
Caffeine body fluid electrolyte balance and exercise performance

Int J Sport Nutr Exerc Metab. 2002 Jun;12(2):189-206.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12187618&query_hl=2

Armstrong LE.

Departments of Kinesiology, Nutritional Sciences, and Physiology & Neurobiology, University of Connecticut, Storrs, CT 06269-1110, USA.

Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be a less risk than athletes because their fluid losses via sweating are smaller.

 
Caffeine ingestion and fluid balance a review

Journal of Human Nutrition & Dietetics
Volume 16 Issue 6 Page 411 - December 2003
doi:10.1046/j.1365-277X.2003.00477.x

http://www.blackwell-synergy.com/links/doi/10.1046%2Fj.1365-277X.2003.00477.x?cookieSet=1

UK; 11 Loveday Road, Ealing, London, UK

Background Caffeine and related methylxanthine compounds are recognized as having a diuretic action, and consumers are often advised to avoid beverages containing these compounds in situations where fluid balance may be compromised. The aim of this review is to evaluate the available literature concerning the effect of caffeine ingestion on fluid balance and to formulate targeted and evidence-based advice on caffeinated beverages in the context of optimum hydration.

Method A literature search was performed using the Medline database of articles published in the medical and scientific literature for the period of January 1966March 2002. Subject headings and key words used in this search were: tea, coffee, caffeine, diuresis, fluid balance and water-electrolyte balance. A secondary search was performed using the bibliographies of publications identified in the initial search.

Results The available literature suggests that acute ingestion of caffeine in large doses (at least 250300 mg, equivalent to the amount found in 23 cups of coffee or 58 cups of tea) results in a short-term stimulation of urine output in individuals who have been deprived of caffeine for a period of days or weeks. A profound tolerance to the diuretic and other effects of caffeine develops, however, and the actions are much diminished in individuals who regularly consume tea or coffee. Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.

Conclusion The most ecologically valid of the published studies offers no support for the suggestion that consumption of caffeine-containing beverages as part of a normal lifestyle leads to fluid loss in excess of the volume ingested or is associated with poor hydration status. Therefore, there would appear to be no clear basis for refraining from caffeine containing drinks in situations where fluid balance might be compromised.
Concentrations of trace elements in sweat during sauna bathing.

Hoshi A, Watanabe H, Kobayashi M, Chiba M, Inaba Y, Kimura N, Ito T.

Department of Health and Physical Education, Nippon Dental University, Tokyo, Japan. ahoshi@tokyo.ndu.ac.jp

Trace elements in sweat during sauna bathing were assessed. Sweat collected by the whole body method was compared with that collected by the arm bag method. The sweat samples were collected from ten healthy male adults aged 22-26 years, by heat exposure in dry sauna bathing (60 degrees C, 30 minutes). Concentrations of major (Na, Cl, K, Ca, P and Mg) and trace (Zn, Cu, Fe, Ni, Cr and Mn) elements in sweat tended to be lower in the arm bag method than in the whole body method. It was found that Ca, Mg, Fe and Mn concentrations in the arm bag method were significantly lower than those in the whole body method. The amount of trace elements in sweat measured by the arm bag method was less than that by the whole body method; significant differences were observed in Fe and Mn amounts. These observations suggest that excretion of trace elements by sweating induces trace element decrease. Therefore, athletes and workers who work in a hot environment and sweat much habitually should ingest adequate amounts of trace elements.
Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=2383801&query_hl=4

Can J Physiol Pharmacol. 1990 Jul;68(7):889-92.

Falk B, Burstein R, Rosenblum J, Shapiro Y, Zylber-Katz E, Bashan N.

Faculty of Health Sciences, McMaster University, Hamilton, Ont., Canada.

This study investigated the effects of caffeine supplementation on thermoregulation and body fluid balance during prolonged exercise in a thermoneutral environment (25 degrees C, 50% RH). Seven trained male subjects exercised on a treadmill at an intensity of 70-75% of maximal oxygen consumption to self-determined exhaustion. Subjects exercised once after caffeine and once after placebo ingestion, given in a double-blind crossover design. Five milligrams per kilogram body weight of caffeine followed by 2.5 mg.kg-1 of caffeine were given 2 and 0.5 h before exercise, respectively. Rectal temperature was recorded and venous blood samples were withdrawn every 15 min. Water loss and sweat rate were calculated from the difference between pre- and post-exercise body weight, corrected for liquid intake. Following caffeine ingestion, when compared with placebo, no significant difference in final temperature or in percent change in plasma volume were found. No significant differences were observed in total water loss (1376 +/- 154 vs. 1141 +/- 158 mL, respectively), sweat rate (12.4 +/- 1.1 vs. 10.9 +/- 0.7 g.m-2.min-1, respectively), rise in rectal temperature (2.1 +/- 0.3 vs. 1.5 +/- 0.4 degrees C, respectively), nor in the calculated rate of heat storage during exercise (134.4 +/- 17.7 vs. 93.5 +/- 22.5 W, respectively). Thus, in spite of the expected rise in oxygen uptake, caffeine ingestion under the conditions of this study does not seem to disturb body fluid balance or affect thermoregulation during exercise performance.
Thermoregulation and body fluid osmolality

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9793803&query_hl=20

Basic Clin Physiol Pharmacol. 1998;9(1):51-72.

Morimoto T, Itoh T.

Department of Physiology, Kyoto Prefectural University of Medicine, Japan.

Thermoregulatory responses induce dehydration, and dehydration itself raises body temperature, causing an increase in the threshold temperature for cutaneous vasodilatation and sweating, the sensitivity of cutaneous vasodilatation in response to a unit rise in body temperature, and the maximum attainable level of cutaneous circulation, and sweat rate. The reduction of these thermoregulatory responses has been related to hypovolemia and hyperosmolality. Evidence showing the involvement of cardiopulmonary baroreceptors is discussed along with an introduction on the effect of hyperosmolality on skin blood flow and sweating and the involvement of central nervous mechanisms. Heat induced hyperosmolality triggers regulatory responses maintaining blood volume and circulatory function, including a fluid shift between body fluid compartments and the control of fluid intake. Evidence showing the importance of the osmotic regulation of body fluid by drinking is also presented. Finally, the effect of hypovolemia and hyperosmolality under thermal stress due to hot environment or physical activity is discussed from the viewpoint of the interaction between circulation, thermoregulation and body fluid homeostasis.