Hyponatremia among runners in the Boston Marathon.
BACKGROUND
Hyponatremia has emerged as an important cause of race-related death and life-threatening illness among marathon runners. We studied a cohort of marathon runners to estimate the incidence of hyponatremia and to identify the principal risk factors.


METHODS
Participants in the 2002 Boston Marathon were recruited one or two days before the race. Subjects completed a survey describing demographic information and training history. After the race, runners provided a blood sample and completed a questionnaire detailing their fluid consumption and urine output during the race. Prerace and postrace weights were recorded. Multivariate regression analyses were performed to identify risk factors associated with hyponatremia.


RESULTS
Of 766 runners enrolled, 488 runners (64 percent) provided a usable blood sample at the finish line. Thirteen percent had hyponatremia (a serum sodium concentration of 135 mmol per liter or less); 0.6 percent had critical hyponatremia (120 mmol per liter or less). On univariate analyses, hyponatremia was associated with substantial weight gain, consumption of more than 3 liters of fluids during the race, consumption of fluids every mile, a racing time of >4:00 hours, female sex, and low body-mass index. On multivariate analysis, hyponatremia was associated with weight gain (odds ratio, 4.2; 95 percent confidence interval, 2.2 to 8.2), a racing time of >4:00 hours (odds ratio for the comparison with a time of <3:30 hours, 7.4; 95 percent confidence interval, 2.9 to 23.1), and body-mass-index extremes.


CONCLUSIONS
Hyponatremia occurs in a substantial fraction of nonelite marathon runners and can be severe. Considerable weight gain while running, a long racing time, and body-mass-index extremes were associated with hyponatremia, whereas female sex, composition of fluids ingested, and use of nonsteroidal antiinflammatory drugs were not.
Almond
Christopher S D
CS
Department of Medicine, Children's Hospital, Boston, MA 02115, USA. christopher.almond@childrens.harvard.edu
Shin
Andrew Y
AY
Fortescue
Elizabeth B
EB
Mannix
Rebekah C
RC
Wypij
David
D
Binstadt
Bryce A
BA
Duncan
Christine N
CN
Olson
David P
DP
Salerno
Ann E
AE
Newburger
Jane W
JW
Greenes
David S
DS
D000704:Analysis of Variance; D001628:Beverages; D015992:Body Mass Index; D015331:Cohort Studies; D004326:Drinking / Q000502:physiology; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000209:etiology*; D016015:Logistic Models; D008297:Male; D012307:Risk Factors; D012420:Running / Q000502:physiology*; D012737:Sex Factors; D012964:Sodium / Q000097:blood; D013997:Time Factors; D014556:Urine; D014867:Water / Q000008:administration & dosage*; D015430:Weight Gain
D014867:Water; D012964:Sodium