August 28, 2017

Water and Staying Hydrated

There is so much controversy surrounding this topic ever since Gatorade was pushed onto the market in the 80's and 90's paralleling the obesity epidemic. We have been told that we need sports drinks in order to perform and prevent dehydration. What is the truth?

From the British Medical Journal:
"Water is the major constituent of the human body and the total body water content is tightly regulated. The goal is to ensure that the water content of the cells and hence their size remains within a homeostatically regulated range.
Humans evolved as long distance persistence hunters on the arid savannahs of south and east Africa. We inherited the capacity to regulate our body temperatures during prolonged exercise in dry heat despite quite large reductions in total body water-no other mammal has the equivalent capacity.

Humans do not regulate fluid balance on a moment to moment basis. Because of our evolutionary history, we are delayed drinkers and correct the fluid deficits generated by exercise at, for example, the next meal, when the electrolyte (principally sodium but also potassium) deficits are also corrected.

As a result, there is no need to completely replace any fluid deficit as it develops either at rest or during exercise. Instead people optimize their hydration status by drinking according to the dictates of thirst."

I think about adaptation again when it comes to this topic. Does it make sense that humans would need a sugary beverage to maintain adequate hydration and if so, why does it not exist naturally on earth?

It turns out from my take on the literature is that thirst is a great indicator of hydration status. There is solid evidence that dehydration is not a major risk of death during sports where as over hydration is. The New England Journal of Medicine published a paper regarding death during marathons from hydration status. They showed that drinking too much is the risk factor for death regardless of beverage consumed from water to sports drinks.

The biggest concern with dehydration is when humans that do not sweat well exercise on very hot days. This causes the persons core temperature to rise quickly and is life threatening. Drinking cool water and placing cooling wet towels on one's head and armpits throughout the workout can mitigate these risks.

When it comes to children and sports, I fall on the side of water is the key and sports drinks have no place in training. Once a person gets to the elite level of olympic sports, then there may be a case for some electrolyte solution because of the prolonged training. Yet, this is still debatable.

Take home points:

1) Hydrate with water when thirsty and increase volumes on super hot days.
2) Pre-hydrating before events makes common sense.
3) Know whether you sweat well or do not and plan accordingly on hot days.

Dr. M

Atlantic Review of BMJ article
BMJ article
New England Journal of Medicine Article
Johns Hopkins Heat Stroke Page