By Dallon Lamarche, B.SC., and Glen P. Kenny, Ph.D.
|Dallon Lamarche, B.SC.||Glen P. Kenny, Ph.D.|
Hydration is of particular importance for everyone participating in exercise and/or work-related tasks. This is especially relevant in hot environments when the body will store excess heat. Recently, researchers have considered whether the temperature of ingested water could play a factor in regulating the amount of heat stored and thereby alter core body temperature. Prior to our publication in the June 2015 issue of MSSE, the media has outlined that consuming hot water resulted in a lower amount of heat stored in the body compared to cold waterdue to an over-compensatory increase in sweating. This counterintuitive notion was based on a recent study which suggested that hot water may help cool the body. However, our recent findings show that ingesting hot or cold water does not influence body heat storage, and thus core temperature regulation during exercise.
In our study, 10 males (19-32 years) cycled for 75 minutes at normal room temperature (25°C) at 50 percent of their maximal oxygen uptake. The exercise was performed in the Snellen whole-body direct calorimeter, which is a device that precisely measures the amount of heat lost over time (through sweat evaporation and dry heat exchange). During exercise, participants consumed either hot (50°C) or cold (1.5°C) water every 15 minutes. We observed a continuous separation in whole-body sweating such that sweating was higher with hot relative to cold water ingestion. However, this difference in sweating was proportionate to the difference in heat content of the ingested water between the temperature conditions, resulting in similar changes in body heat storage. Therefore, we showed that, during moderate prolonged exercise, the human body adjusts the sweating response to compensate for the heat content of the ingested water—no less and no more—such that heat balance is maintained.
Our findings indicate that the temperature of ingested water does not have a direct influence on body temperature during exercise. However, one cannot ignore the different behavioral and psychological effects that water of different temperatures may have on maintaining adequate hydration. For instance, the palatability of cold water is shown to clearly be more favorable during prolonged exercise in comparison to hot water. When provided the option to drink cold water at will in one session and hot water in another, a group of investigators demonstrated several years ago that individuals will ingest much more cold water (by about 37 percent). This has important implications for the athlete and the worker because individuals are more inclined to drink cold water during physical activity which leads to a better maintenance of hydration and core body temperature regulation. In addition, cold water ingestion has been shown to improve performance, as evidenced by extended time to exhaustion and lower perceived exertion in performance based events when compared to ingesting hot water. On the other hand, drinking hot water during exercise is not pleasant as anecdotally reported by the participants in our study and, consequently, may hinder performance through behavioral and psychological modifications.
Ultimately, our message is clear: athletes and workers should consume water at cooler (or “more comfortable”) temperatures during physical tasks as opportunities allow. In the end, the consumption of water itself is the most important consideration for hydration status.
Viewpoints presented on the ACSM blog reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Dallon Lamarche is a recent bachelor of science graduate with specialization in human kinetics at the University of Ottawa, Canada. He completed the study highlighted in this commentary at the Human and Environmental Physiology Research Unit as part of his senior year research project requirements under the supervision of Dr. Glen P. Kenny.
Glen P. Kenny is a professor of exercise physiology at the University of Ottawa, holds a university research chair in environmental physiology and is a member of ACSM. His research has been directed at characterizing the physiological control mechanisms governing human temperature regulation during heat stress. An area of special focus in his work is the investigation of the physiological effects of heat stress in subpopulations with conditions rendering them particularly vulnerable to heat injury, such as aging, obesity and diabetes.
This commentary presents Mr. Lamarche’s and Dr. Kenny’s views on the topic related to a study which they and colleagues recently completed. Their research report appears in the June 2015 issue of Medicine & Science in Sports & Exercise® (MSSE).