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Paper
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Hyponatremia among Runners in the Boston Marathon[1]
Summary
A prospective cohort of the 2002 Boston Marathon enrolled 766 runners; 488 (64%) provided usable finish-line blood samples with pre/post-race weights and survey data. Hyponatremia (Na ≤135 mmol/L) occurred in 13% (62/488) — 22% of women and 8% of men — with critical hyponatremia (≤120 mmol/L) in 0.6% (3 runners; values 119, 118, 114). On multivariate analysis the dominant risk factors were weight GAIN during the race (OR 4.2; 2.0 per kg) and racing time over 4 hours (OR 7.4 vs <3:30; 1.6 per 30 min); BMI extremes were also associated. Female sex, fluid composition, and NSAID use were not significant after adjustment — fluid volume consumed (colinear with weight gain) drives risk.
Key findings
- 13% (62/488) of sampled finishers hyponatremic; 22% of women, 8% of men; 0.6% critical (≤120 mmol/L).
- Weight gain during the race: OR 4.2 (2.2–8.2); per-kg OR 2.0 (1.6–2.6).
- Racing time >4:00 h: OR 7.4 (2.9–23.1) vs <3:30; per-30-min OR 1.6 (1.3–2.1).
- Female sex, fluid composition, NSAIDs not significant after adjustment — overdrinking (weight gain) is the modifiable driver.
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- PubMed ↗abstract · free