Hydration is a sports safety issue that has, in the past, been misunderstood. Dehydration is a myth that has been perpetuated by the marketing of sports drinks as essential to performance. Dehydration, in fact, is not a medical illness (Noakes, 2012).

“Over the past 40 years humans have been misled—mainly by the marketing departments of companies selling sports drinks—to believe that they need to drink to stay “ahead of thirst” to be optimally hydrated. In fact, relatively small increases in total body water can be fatal. A 2% increase in total body water produces generalised oedema that can impair athletic and mental performance; greater levels of overhydration result in hyponatraemic encephalopathy— severe cerebral oedema that produces confusion, seizures, coma, and ultimately death from respiratory arrest” (Noakes, 2012).

Humans have a built-in mechanism – thirst – that tightly regulates hydration levels, and as such it is not necessary to continually re-hydrate when exercising if not thirsty. It has been shown that drinking to thirst is sufficient to maintain performance (Noakes, 2012). Children should be reminded to drink when exercising, but be taught to drink only if thirsty.

Recent research (Saker et al, 2014), discussing regional brain responses associated with drinking water during thirst and after its satiation, found that drinking water in response to fluid loss (thirst) is a pleasant experience, however drinking water after thirst has been satiated is unpleasant.  The authors concluded that “the pleasantness of drinking when thirsty is associated with activation in the anterior cingulate cortex and orbitofrontal region. The unpleasantness and aversion of overdrinking is associated with activations in the midcingulate cortex, insula, amygdala, and periaqueductal grey” (Saker et al, 2014). These brain regions allow us to recognise when we have satisfied our need for water. Further forced drinking over and above this need can lead to the negative consequences, as outlined by Noakes above.

When exercising in the heat, it has been shown that hyperhydration (drinking to prevent dehydration rather than to thirst) provides no advantages over euhydration (normal bodily water levels) regarding thermoregulation and exercise performance in the heat (Sawka et al, 2001). This is supported by a study in 2013 that stated that “current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat” (Wall et al, 2013). This research found that, when well-trained athletes exercised under real-world outdoor conditions without knowing their hydration status, their performance, physiological and perceptual variables did not differ between trials under differing conditions. This adds to the growing body of knowledge that supports the drink-to-thirst model.

A recent tweet from one of the authors of the study, @PaulBLaursen, sums up the performance and hydration nexus:

The brain guides hydration level emotionally with thirst. Fatigue = emotion. This is likely why performance is maximised when drinking to thirst.

I highly recommend Noakes’ evidence-based book “Waterlogged” for more information on the myth of dehydration.

A recommended article on The Sport In Mind about hydration

ReferencesShow all

Noakes TD. 2012. Waterlogged: the serious problem of overhydration in endurance sports. Human Kinetics.

Saker P., Farrell M.J., Adib F.R.M, Egan G.F., McKinley M.J., Denton D.A. 2014. Regional brain responses associated with drinking water during thirst and after its satiation. Proceedings of the National Academy Sciences of the United States of America. 111(14): 5379–5384.

Sawka, M. N., Montain, S. J., Latzka, W. A. 2001. Hydration effects on thermoregulation and performance in the heat. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 128(4), 679-690.

Wall, B. A., Watson, G., Peiffer, J. J., Abbiss, C. R., Siegel, R., Laursen, P. B. 2013. Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat. British Journal of Sports Medicine online first.