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Hyponatremia in runners: The dose makes the poison

Pictured at the 2005 Boston Marathon are researchers (l to r): Bryce Binstadt, MD, PhD, Christopher Almond, MD, MPH, Christy Duncan, MD, and Andrew Shin, MD.

"Drink, drink, drink," has long been the runner's mantra, but a study from Children's Hospital Boston finds that over-hydration is a bigger problem than previously thought, especially among non-elite runners. Led by cardiac fellow Christopher Almond, MD, the study surveyed 488 runners in 2002's Boston Marathon about their fluid intake, analyzed blood samples and recorded their weights before and after the race. Thirteen percent of runners finished with hyponatremia, a condition that in rare instances can be fatal (as it was for one 2002 runner). The major reason for the dip in blood sodium was excessive fluid intake: 48 percent of hyponatremic runners drank more than 3 liters during the race, versus only 26 percent of runners without hyponatremia. Surprisingly, runners who drank electrolyte-containing sports drinks, as opposed to plain water, had the same risk. Runners who gained weight during the race due to fluid loading were at especially high risk, as were slower runners and those with a lower body mass index. The study appeared in the April 14 New England Journal of Medicine.