Risk factors for exercise-associated hyponatremia in Non-elite marathon runners

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Chorley, J., Cianca, J., Divine, J. (2007). Risk factors for exercise-associates hyponatremia in non-elite marathon runners. Clinical Journal of Sports Medicine (17)6, 471-477.


The purpose of this study was to examine the relationship between the development of decreases in post-race serum sodium (Na+) levels and exercise-associated hyponatremia (EAH), between the risk factors of non-elite marathon runners. Risk factors include low body weight, female gender, slower running time, excessive drinking, and altered renal excretory capacity (Chorley, Cianca, Divine, 2007). Hyponatremia or low sodium levels in prolonged endurance events can lead to nausea, dizziness, confusion, and even death.

This was a longitudinal study conducted at the Houston Marathon from 2000-2004, and consisted of ninety-six runners (2000, N = 10; 2001, N = 44; 2002, N = 32; 2003, N = 6; 2004,
N = 4). The runners were recruited from the local running community and volunteered with completed informed consent before participating in the study. An independent t-test was used to determine if a difference exists between baseline characteristics and physiologic estimates of hyponatremic and normonatremic runners, and those who lost 0.75 kg or more or failed to lose 0.75 kg during the race. There were many significant values related to difference by weight change category. Including the measured values of: 
Post Na+ and change of Na+, finish time, fluid consumed, sweat rate, and fluid balance), as compared to 1) Those Who Lost at Least 0.75 kg, and 2) Those Who Lost Less Than 0.75 kg.

Significance was also established for many of the baseline characteristics and physiologic estimates by hyponatremia status. Determinates of hyponatremic (N=19) versus normonatremic (N = 77) runners of measured values included:
Pre-race weight, weight change, post-race Na+, change in Na+, intake of total cups of fluid, water intake, and fluid ingestion rate in mL/hr. Estimated values included: Fluid ingestion rate in mL/hr., and fluid balance in mL/hr. .

The significance between variables in this study confirms the seriousness and the influential factors of hyponatremia in recreational marathon runners. Runners who did not lose weight and consumed more fluid, mainly water are more likely to experience hyponatremia and lower post -race Na+. “A combination of fluid overconsumption beyond sweat rate and inappropriate fluid retention can explain the pathophysiologic process of EAH that accounts for a portion of decreased serum Na+ in marathon runners” (Chorley, Cianca, Divine, p. 474, 2007). In addition, the pathophysiology associated with perception of thirst and overconsumption of fluid, and the mechanism of the syndrome of inappropriate antidiuretic hormone (SIADH) has been compromised in marathon runners which contributes to the effects of hyponatremia. This study proves the need for education on appropriate individualized fluid strategies for non-elite runners.

MA

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