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Thirst First: The Hydration Lie

​​It's been hot lately. Very hot. A normally easy-ish ten mile train run yesterday turned into a sodden-shirted slog as I stumbled towards Henley seeing mirages of cool oases.

Of course, according to 'conventional' wisdom the moment I felt thirsty it was 'too late'. I was irredeemably dehydrated by at least 2% and my performance would now drop by at least 10%, possibly 20%. That's huge! I would definitely need to walk. Yet weirdly, as my final destination drew near I managed to up my pace and finish the last two miles in 14 minutes.

Most of what we think we know about hydration is based on research conducted by drinks companies - principally Gatorade. Before Gatorade came along (and yes, it was the first 'sports' drink), there were all sorts of theories regarding drinking fluids while exercising with some athletes and coaches recommending drinking nothing at all. Yet there are few historical instances of runners finishing marathons in dangerously dehydrated states, dead on their feet and crawling over the line.

Even now, the faster marathon runners typically finish a race having lost about 5% of their body weight in sweat. Yet they also, typically, run the second halves of their races quicker than the first. Certainly their performances don't drop by 20-40%. And they don't cross the line and promptly pass away.

In fact, I'm not aware of any cases of 'death-by-dehydration' in the history of the marathon. Yet the advice to drink, drink and drink some more to avoid dehydration at all costs has become so prevalent that in the 1990s we began to see a huge rise in cases of hyponatremia (essentially, 'over-hydration') and, yes, people died. De-hydration is easy to cure – give someone a drink of water. But hyponatremia is extremely difficult to deal with and cases can quickly lead to coma and, without quick hospitalisation, death.

There are plenty of reasons why Gatorade's research and the subsequent advice is flawed. Anyone interested in digging a little deeper should read the excellent 'The Runner's Body' by Ross Tucker and Jonathan Dugas, two of the most respected sports scientists in the world today. But we can keep things simple...

Man has evolved over millennia. For all but 50 years of those millennia we have survived intense demands on our bodies, often with little access to water of any kind, let alone a sports drink. Not only have we survived, we've thrived. The reason is that we developed a very sophisticated system to mange our hydration levels. It's called 'thirst'. If you're thirsty, you need a drink of water.

'...your thirst mechanism is one of the most sensitive, well-developed and exquisite mechanisms you have. If you simply obey it, you will never run into any dangers with dehydration or heatstroke. Therefore, drink according to thirst, no more, no less, and you will optimise both performance and health.' – The Runner's Body by Ross Tucker and Jonathan Dugas (Rodale, 2009)

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