Specializing in Spine, Sports & Physical Medicine

Drink, drink, drink….how much should we drink during exercise?

How much do you really need to drink while exercising to prevent loss of performance and dehydration?

This is a very timely topic. The rate of Exercise associated hyponatremia (EAH) has been on the rise over the past 30 years. Before that it was very uncommon. Hyponatremia means low blood sodium levels. Many endurance athletes are under the impression this comes from loss of sodium and other electrolytes through sweating. While it is true that we all lose sodium through our sweat, and on really hot days it is more, the body over millions of years has developed complex mechanisms to keep the blood concentration of sodium in a very narrow range. This is even if you lose salt through your sweat. If an athlete overcompensates and takes in more fluid than is necessary to keep up with thirst and dilute their blood and sodium levels drop. This can result in EAH. This can make you very sick and can even lead to death.

It is currently estimated that between 0.3% and 13% of marathon runners finish the race with medical evidence of EAH, and the worldwide incidence is increasing in spite of the mechanisms and causes being well known.

In a recent study of 197 runners solicited by personal solicitation, e-mail and flyers distributed at three local races in autumn 2009, participants were asked about their beliefs regarding fluid replacement during exercise.

Most runners (58%) stated that they drink only when thirsty. Gastrointestinal distress was the most frequently cited (71.5%) reason to avoid overhydration. It was found that runners have a poor understanding of the physiological consequences of hydration behaviours that frequently reflect messages of advertising.The conclusion of the study was that runners at highest risk of EAH exhibit behavior that is shaped by their beliefs about the benefits and risks of hydration. These beliefs are frequently based on misconceptions about basic exercise physiology.

To try and reduce the incidence of EAH the International Marathon Medical Directors Association and United States of America Track and Field now recommend drinking to the dictates of thirst, although, the global marketing of sports drinks continues to promote over drinking.

I’d love to hear your thoughts on this……..when you exercise do you drink only when thirsty?

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