Fluid Balance in Runners: Getting it Right
abstract & commentary
By Joseph E. Scherger, MD, MPH
Clinical Professor, University of California, San Diego
Disclosure; Dr. Scherger reports no financial conflicts to this field of study.
Synopsis: Hyponatremia is now considered a greater risk in long distance runners than dehydration, given the emphasis on consuming sports drinks and water. Thirteen percent of a prospective sample of finishers of the 2002 Boston marathon, and 22% of the women, had hyponatremia at the finish. Risk factors included a longer running time and frequent ingestion of fluids.
Source: Almond CSD, et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med. 2005;352:1550-1556.
In the 2002 boston marathon, almond and colleagues, enrolled 766 runners to participate in a study measuring serum sodium at the finish line. No fluid instructions were given. 488 of the runners provided a usable blood sample at the end of the race. While the mean serum sodium was 140 mmoL/L, 62 of the finishers (13%) had hyponatremia (serum sodium below 135 mmoL/L); and 22% of the female runners had hyponatremia. Three of the runners (0.6%) had serum sodium below 120 mmoL/L. None became ill, however one 28-year-old female runner in the same race collapsed and died of hyponatremia after drinking excessive amounts of fluids, including 16 ounces of a sports drink after the finish thinking that her dizziness may be due to
dehydration.1
In this study, the runners at greatest risk of hyponatremia were those spending more than 4 hours to
complete the race, women, the very thin and overweight.
Commentary
On the day I’m writing this, I was captain at a medical aid station at the San Diego Rock N Roll Marathon, June 5, 2005. Lewis Maharam, MD, from New
York2 was medical director and has 25 years experience directing medical teams at marathons, including the New York City marathon. He has been studying and monitoring the fluid balance issue in long distance runners for many years. He provided the medical volunteers and all the runners with current information on fluid balance to avoid both dehydration and
hyponatremia. He and other experts believe that hyponatremia
is the greater threat given the number of fluid stations along the race and the marketing of sports
drinks.3
While fluid intake may vary with the weather conditions, a general rule of one cup every 20 minutes of running seems to provide consistently good results. To my amazement, salt was handed out to runners at the beginning of the race and once during the race. This goes against all my early medical education condemning giving salt to athletes. Apparently, long distance runners have fluid retention during the run and will dilute their serum from excessive drinking. Sports drinks add glucose which helps avoid lactate buildup in muscles, but are not different than water with respect to the issue of hyponatremia.
So, drink fluids—but not too much—is the current
message to endurance athletes. Today it seems that anybody will try and run a marathon. In the first running boom of the 1970s, most runners were training
hard and shooting for low times. In today’s second running boom, the most common runner is just trying
to finish and may be part of a fund-raising benefit. These inexperienced runners take longer to complete
the race and may be irrational in their use of fluids. It is important for all physicians to give specific advice
on fluid balance for those participating in endurance
athletic events.
As an aside on medications, NSAIDs are not recommended since they may contribute to fluid retention and hyponatremia.3 Acetaminophen is analgesic of choice, but even that must be used with some caution. Lewis Maharam tells the story of one woman runner/walker who during the Country Music Marathon ingested acetaminophen at every medical aid station. She was hospitalized for an overdose. As 20,000 or more runners participate in these events, anything can and will happen.
References
1. New York Times, April 14, 2005.
2. Lewis G. Maharam, MD, FACSM, [email protected].
3. Davis DP, et al. J Emer Med. 2001;21:47-57.
By Joseph E. Scherger, MD, MPH Clinical Professor, University of California, San Diego Disclosure; Dr. Scherger reports no financial conflicts to this field of study.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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