Hydration: Too Much of a Good Thing?

Dehydration warnings and preventive measures tend to dominate endurance performance nutrition advice. It is well established that dehydration has a negative impact on health and performance. Severe dehydration is life threatening although rare in standard endurance events. Although moderate dehydration may not be life threatening it can affect performance. In matters of performance, Dr. Barr of UBC in Vancouver published in1999, that just a 2% reduction in body fluid weight can result in a 1.8-2% negative performance result. A 2-3% fluid loss produces a 7% reduction in performance.

Since 1984, a growing number of athletes requiring emergency medical tent attention following endurance events including standard marathons, ironman triathlons and long distance bicycle races have been diagnosed with over hydration (also known as ‘water intoxication’ or the medical term ‘hyponatremia’).

D B Speedy from the University of Auckland in New Zealand published in 2001 that as little as 2% “over hydration” can cause life-threatening hyponatremia. Several deaths due to hyponatremia have been reported since 2000 at events like the Jacksonville marathon, the Boston Marathon, and Ironman events.

So it has now become clear that, you need to get your hydration needs just right. Hydration must be coupled with adequate sodium intake; sodium losses can be significant during prolonged exercise. Barr and associates observed an average loss of 12 g salt in six hours of cycling at 86 degrees F (30 degrees C) and 30% relative humidity (2 g more than the average daily intake of 10 g).