Serum sodium changes in marathon participants who use NSAIDs

Introduction. The primary mechanism through which the development of Exercise-Associated Hyponatremia (EAH) occurs is excessive fluid intake. However, many internal and external factors have a role in the maintenance of total body water and Non-Steroidal Anti-Inflammatory medications (NSAID) have been implicated as a risk factor for the development of EAH. This study aimed to compare serum sodium concentrations ([Na]) in participants taking an NSAID before or during a marathon (NSAID group) and those not taking an NSAID (control group). Methods. Participants in a large city marathon were recruited during race registration to participate in this study. Blood samples and body mass measurements took place on the morning of the marathon and immediately post- marathon. Blood was analysed for [Na]. Data collected via questionnaires included athlete demographics, NSAID use and estimated fluid intake. Results. We obtained a full data set for 28 participants. Of these 28 participants, 16 took an NSAID on the day of the marathon. The average serum [Na] decreased by 2.1mmol/L in the NSAID group, whilst it increased by 2.3mmol/L in the control group NSAID group (p=0.0039). Estimated fluid intake was inversely correlated with both post-marathon serum [Na] and ∆ serum [Na] (r=-0.532, p=0.004 and r=-0.405 p=0.032, respectively). Conclusion. Serum [Na] levels in participants who used an NSAID decreased over the course of the marathon whilst it increased in those who did not use an NSAID. Excessive fluid intake during a marathon was associated with a lower post-marathon serum [Na].