Risk Factors for Hyponatremia among Runners in the Boston Marathon

• Published in: Academic emergency medicine 2003-05, Vol.10 (5), p.534-535
• Main Author: Almond, C. S
• Format: Article
• Language: English
• ISSN: 1069-6563; 1553-2712
• DOI: 10.1197/aemj.10.5.534-b

OBJECTIVES: The objective of our study was to identify risk factors for exercise-associated hyponatremia in marathon runners. METHODS: Official participants in the 2002 Boston Marathon were recruited prospectively at an exposition 1-2 days before the race. Subjects completed a survey describing demographic information and training history. Following the race, runners provided a blood sample and completed a questionnaire detailing fluid consumption during the race. Pre- and post-race weights were measured. We determined a priori that age, female gender, smaller body surface area (BSA), poorer conditioning, longer race times, lower percentage of weight loss, and consumption of predominantly free water should be considered as potential risk factors for hyponatremia. Chi-square and unpaired t-tests, along with binary logistic regression techniques were employed. RESULTS: Of 741 runners enrolled, 481(64%) had blood drawn after completing the marathon. Subjects had a mean age of 39 +/- 9 years. 165 (34%) were female. Mean race time was 219 +/- 48 minutes. Mean serum sodium was 140 +/- 4.8 mEq/L. Sixty-two (13%) subjects developed hyponatremia (serum sodium less than 135 mEq/L). Three subjects (1.2%) had serum sodium values less than 120 mEq/L. On univariate analysis, female gender, race time >/=4 hours, BSA /=4 hours (OR 2.7, 95% CI 1.4 to 5.1), female gender (OR 3.4, 95% CI 1.2 to 9.7) and post-race weight >/= pre-race weight (OR 4.0, 95% CI 2.1 to 7.7). CONCLUSION: Exercise-associated hyponatremia occurred in approximately 13% of subjects completing the Boston Marathon. Female runners and runners with slower race times are at higher risk. Our findings also suggest that excess fluid consumption before or during marathoning may contribute to the risk of hyponatremia.