Hydration: How Much Is Too Much Water?

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For years the military has been at the fore-front of experiments using humans and their recent tests on hydration are following suit. The April 2009 study examined volunteers in a laboratory “under varying conditions of work intensity and duration, environmental conditions such as temperature and humidity, and types of clothing.” Some of these variable were chosen in order to better refine, and perhaps replace, the formula that has been used since 1982 to determine sweat rate and water needs. Water accounts for a large percentage of the military’s cost when sending soldiers overseas. They must take into account it’s price, storage, piping, distribution, sourcing, etc so honing in on the needs is paramount to a successful mission. This new formula shows promise at being more accurate and allows for water needs to be estimated for a person working 8 hours vs the old standard of 2 hours. Technology has brought about changes in clothing that helps soldiers with temperature regulation and thus changes their sweat rate and the amount of water they need to stay hydrated. Early indicators show the new formula to be accurate and reproducible so it may taken into the field for further testing. The researchers do note that the formula may be made more exact by including a variable of the subject’s fitness level. People with varying fitness levels also have varying hydration needs.

Hydration For Weekend Warriors?

As it stands now, the calculations and measurements are too complex for the general public to be able to use when determining adequate hydration for themselves.  The researchers note that “It contains many variables, reflecting the complexity of predicting sweat loss, such as skin temperature and amount of energy expended.” The hope is to develop formulas or metrics so that the public does have access to a workable formula. Ideally this  information may be used when a disaster strikes and hydration needs are being assessed, as well as when relief efforts or public projects are being undertaken. Given the importance of hydration and its ability to affect performance and to maintain life, the efforts of these researchers needs to be applauded and their updates should be kept on the radar.

Richard R. Gonzalez, Samuel N. Cheuvront, Scott J. Montain, Daniel A. Goodman, Laurie A. Blanchard, Larry G. Berglund, and Michael N. Sawka. EXPANDED PREDICTION EQUATIONS OF HUMAN SWEAT LOSS AND WATER NEEDS. Journal of Applied Physiology April 30, 2009.


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