Dysnatremia in Relation to Frailty and Age in Community-dwelling Adults in the National Health and Nutrition Examination Survey

Background: Frailty represents an age-related state of increased risk of adverse health outcomes, reflecting some combination of increased damage and compromised repair processes. Our objectives were to establish whether frailty is associated with dysnatremia (a deviation of serum sodium from normal values), to determine whether frailty explains the previously established association between age and dysnatremia and to assay the impact of each on mortality.

Methods: The relationship between age, frailty, and dysnatremia was investigated across the adult life course in 8,911 respondents from the 2003-2004 and 2005-2006 cross-sectional National Health and Nutrition Examination Survey, on whom both laboratory and mortality data were available. A frailty index (FI) was calculated for each respondent and related to dysnatremia (serum sodium values outside a 136-144 mmol/L reference range).

Results: Dysnatremia was significantly related to both age and frailty; as the degree of frailty increased, so did the proportion with dysnatremia, for example, from 4.1% in those with FI less than 0.10, to 12.4% in those with FI 0.40 or more; p less than .001. Adjusted for frailty, the relationship between age and dysnatremia was no longer significant. In the age- and sex-adjusted Cox models, both frailty (hazard ratio [HR]: 1.05; 95% confidence interval [CI]: 1.04-1.05 for every 0.01 increase in FI) and dysnatremia (HR: 1.85; 95% CI: 1.51-2.26) were significant predictors of mortality; when hyponatremia was separated from hypernatremia in the Cox models, hypernatremia wasn't significant, but only 41 participants were identified as hypernatremic.

Conclusion: Increasing frailty is associated with dysnatremia and confounds the association between age and dysnatremia.