ICE-COLD WATER AND YOU
There are lots of myths about drinking ice-cold water (hydration) and regulating the temperature of the body. No question, a glass of ice-cold water on a hot day gives you tremendous satisfaction by cooling your mouth and stomach. But does it really satisfy your thirst? Does it deliver water immediately to all your tissues and cells? Does it cool down your body, and reduce its temperature?
I have no idea where these opinions come from, either from somebody's personal experience of cooling perception or just from anecdotal info passed from one friend to another. Theoretically, according to "The Biology of Human Survival" (Claude A.Piantadosi, Oxford University Press, 2003, p.86) "a 70-kilogram person can drop body temperature approximately 1°C by drinking a liter of water at 0°C ", but in reality it is difficult to imagine somebody using this amount of cold water at once during racing activity. Using it in small portions will practically reduce the cooling effect, because heat-cold exchange will be imperceptible on the whole body scale.
I found no data supporting the idea that drinking cold water reduces the body's temperature. If it were so, we would have had it somewhere recorded in human history experience. The law of survival would inevitably recruit this procedure in human life in extreme hot weather conditions. The fact is that we do the opposite to cold water drinking. Survival in severe hot environment includes specific behavior, aimed at reduction of heat by using shelters; wearing thick clothes and making the body sweat by drinking hot tea.
As we know, our body looses liquid through sweating by drops or by small portions over time, so replenishing it should happen almost in the same manner. Thus taking a big portion of water at once would not do the trick, as it may stay in the stomach for a while before it can be absorbed on a cellular level. Additionally, I'd like to bring up here another interesting fact about drinking. The author of the book, mentioned above, wrote, "it is important to note that the main stimulus of drinking is thirst, which is regulated by plasma osmolarity, not by temperature".
Therefore temperature influences our thirst only indirectly through making our body sweat and loose body liquid. Evaporation of this sweat, in its own turn, produces cooling effect. So it has nothing to do with drinking ice-cold water. Morever, when we drink cold water, it can't be absorbed immediately, because it takes time for it to be heated up to achieve the body temperature to be absorbed on a cellular level.
Now we have some logical facts showing us the true and mythical sides of ice-cold water drinking, which have no real cooling effect and should not be used as a body temperature reducing mechanism. It doesn't quench our thirst or reduce our dehydration more effectively than for instance normal temperature water. What it really does for us is giving a pleasant feeling of cold in the mouth and stomach - which are just a perception.