Since the 1980’s athletes have been encouraged to stay ahead of thirst. With the aid of heavily marketed sports drinks formulas laden with salt and sugar, an athlete should stay hydrated during performance and replace any electrolytes lost as well as having a constant energy top up. Hydration mania became a global phenomenon until 2007 when a fitness instructor died in The London Marathon from exercise, induced hyponatraemia, otherwise known as water toxicity.
Fluid replacement is intended as a performance strategy. Mild dehydration is considered to have a negative effect on aerobic exercise performance (1). To this aim, fluids have been readily available at most sporting events and endurance athletes in particular, are still encouraged to combat the effects of sweating with water loading behaviour. Although advice about hydration has been revised to say that thirst should now dictate fluid intake, the American College of Sports Medicine are still saying that we should avoid a two per cent drop in hydration (2). But how can we measure that and in our endeavour to do so are we not still in danger of losing too much sodium?
Most cells in the body can cope with this but brain cells trapped within the skull cannot. This causes the brain to swell leading to confusion, loss of consciousness and seizures. Are we really meant to be constantly dicing with death for the sake of putting in a good performance or is it really all in the mind and we should really try a different focus?
In fact our very survival depends on it! It is so important that drinking too much water is much more dangerous than drinking too little and our body will do anything it can to prevent this. And so it must be that water regulation is really all about the preservation of sodium, so how do we do this?
Contrary to popular opinion, our body does not measure the amount of water in the blood at all. It measures the osmolarity. This is the concentration or thickness of the blood which depends on the quantity of solutes such as salt in it. Because there is always a set point, if it gets thicker we get thirsty and we do not pee it out and when it gets thinner the opposite happens. All of this is regulated and controlled by a centre in the brain where the neurons actually shrink when the blood is too thick. At this point the brain is forced to acknowledge that the osmolarity needs to change and it creates thirst. This shrinking brain cell system probably accounts for eighty per cent of all the headaches we get and certainly most of the hangovers! If things get so bad the body can even take water out of tissues and discs just to stop the shrinking.
We are encouraged to drink small amounts throughout the day, keeping a water bottle by our side. The trouble with this is we could be continuously drinking but insufficient amounts throughout the day and the brain can lose its grip on what the sodium situation is. The set points constantly change until we do not even feel thirsty anymore and yet we are. This can then manifest itself in hunger or pain. Worse still, the body interprets this as an emergency situation and in an emergency, energy gets the highest priority. Our cells bail the water out and allow the fat to come in. For every litre of water we lose from out tissues, we exchange it for one kilo of fat!
And what is wrong with simple water as drinks thick with solutes must drive up thirst as the osmolarity rises? This was a completely natural reaction when we were children, to quench our thirst after extreme bouts of physical activity. We would drink and drink until we had reached satiety and then not till we were thirsty again. Let’s face it, water toxicity was never an issue then and yet it has become embedded in our psyche to do completely the opposite now. Drinking without thirst can’t be right!
