Staying hydrated is crucial for both general health and sport performance. On the surface, it seems like staying hydrated should be pretty easy, right? When you get thirsty, drink more, and it’s all good. Unfortunately it isn’t that simple.
Our thirst response is actually very complex, and is governed by numerous physiological, sociological, and psychological cues. At rest, it’s fairly easy to maintain hydration status, and the recommendation of “drink to thirst” is usually enough. However, numerous studies have shown that during exercise, the human thirst mechanism is likely insufficient to maintain proper hydration, a phenomenon known as “voluntary hydration”. In multiple research studies in which subjects had free access to fluids, subjects voluntarily replaced only 66-75% of their net water loss due to exercise.
Why is this such a big deal? Well, a large body of evidence has shown that mild dehydration of only 1-2% is enough to decrease exercise performance capacity, cognitive function, and alertness, while increasing physiological strain. The earliest mechanisms to elicit a thirst response aren’t initiated until approximately 2% dehydration, at which point it’s already too late and performance is compromised!
So if our own thirst isn’t enough, and if we don’t drink enough even after we’re thirsty, what the heck do we do and how can we tell if we’re consuming enough water? Fortunately, there is a very easy way to monitor your own hydration: the color of your pee! Dr. Lawrence Armstrong, a world-renowned expert on exercise and hydration, is largely credited with introducing urine color as a valid field measure of overall hydration status. Dr. Armstrong introduced a 1 through 8 scale, correlating with urine color:
Start paying attention to your urine color, the lighter the better! Dehydration due to exercise is inevitable, so the more you as an athlete can do to take responsibility for your hydration, the better your performance will be. A good rule of thumb is to look to replete with 20 ounces of water for each pound of body weight lost during an exercise bout, and DON’T WAIT UNTIL YOU’RE THIRSTY!!
P.S. – One important caveat is that certain foods (mostly dark leafy greens), medications (typically antimalarial drugs and certain antibiotics), and vitamins (particularly multivitamins) can impact urine color, in particular leading to a bright neon or even greenish color. For foods and vitamins, this is mostly due to consumption of B vitamins, particularly riboflavin/B2. If this is the case, keep eating your veggies but quit wasting your money on multivitamins 🙂
Armstrong, L.E. (2005). “Hydration Assessment Techniques”, Nutrition Reviews 63:6, S40-S54
Armstrong, L.E., Maresh, C.M., Castellani, J.W., Bergeron, M.F., Kenefick, R.W., LaGasse, K.E., and Riebe, D. (1994). “Urinary Indices of Hydration Status.”, Int. J. Sport Nutr., 4, 265-279.Armstrong, L.E., Herrera Soto, J.A., Hacker, F.T., Casa, D.J., Kavouras, S.A., Maresh, C.M. (1998). “Urinary indices during dehydration, exercise, and rehydration.” Int. J. Sport Nutr. 8: 345-355. Maresh, C.M., Gabaree-Boulant, C.L., Armstrong, L.E., Judelson, D.A., Hoffman, J.R., Castellani, J.W., Kenefick, R.W., Bergeron, M.F., Casa, D.J. (2004). “Effect of hydration status on thirst, drinking, and related hormonal responses during low-intensity exercise in the heat” J Appl Physiol 97: 39–44
Hughes, F., Mythen, M., Montgomery, H. (2018). “The sensitivity of the human thirst response to changes in plasma osmolality: a systemic review.”, Perioperative Medicine 7:1