Rehydration and salty sweat

During a visit to my endospecialist (don’t ask) I picked up a copy of Triathlon magazine that contained an article about the science of hydration by Andy Blow. Andy is described as one of Britain’s finest tri coaches who includes Jenson Button and Fernando Alonso among his clients. Blow writes that loss of sodium is unpredictable and is determined by genetics. He adds that losses in sweat in a normal population can vary eight fold from 230mg/l to 1700mg/l The problem can be further increased if the athlete is a heavy sweater.

Now this didn’t seem likely to me. I believe that the body is a smart organism that has most of the bases covered. Think of two cavemen building an extension to their cave in Southern Africa. One is a heavy sweater with a very high sodium concentration. He could be losing 1700mg of sodium an hour. His buddy is a light sweater with a low sodium concentration so he is losing 115mg of sodium an hour. If you believe Blow this unhappy situation is down to chance. Now in Blow’s world the first caveman just takes in more salt, maybe he necks two Gatorades every hour! In reality these two guys will have similar salt consumption and in all likelyhood will not be able to vary it.

As one of the many oldsters with borderline hypertension I have a passing interest in sodium chloride and I recalled that I had read something about this very topic. As long ago as 1949 Dr Jerome Conn of the University of Michigan medical school carried out research on men carrying out work in an hot environment. He found that the sodium content of sweat varied from 40mg/l to  400mg/l. He found similar differences in the sodium content of urine.

So far so good, Blow and Conn are in agreement. But Conn discovered why there is such a massive variation in sodium content of sweat, In short the more sodium in your diet the more sodium in your sweat. This is the bodies more or less successful attempt to keep the sodium level constant. And isn’t that just what you would expect? Why would the body sweat out sodium leaving the body with a deficiency that could result in cramps and much worse.

My recommendation is to add half a cup of orange juice for the potassium content to a bottle of water. if you expect to sweat very heavily by all means add a quarter teaspoon of table salt just in case. This is based on the presumption that as a cyclist you care about your health and you are already on a low salt diet.

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