Serum sodium in relation to various domains of cognitive function in the elderly US population.

Background: Recent evidence suggests that sodium imbalances may be associated with cognitive impairment; however, the association between specific domains of cognition remains unclear. This study examines the association between serum sodium levels and immediate and delayed verbal memory as measured by the CERAD Word Learning Test (CERAD WLT), executive function as measured by the Animal Fluency test (AFT), and sustained attention, working memory, and processing speed as measured by the Digit Symbol Substitution test (DSST) in the elderly population of the US aged 60 and older who participated in the 2011-2014 National Health and Nutrition Examination Surveys (n = 2,541).

Methods: Cognitive function tests were performed by trained interviewers and sodium levels were measured using indirect ion selective electrode methodology.

Results: After adjusting for all covariates, quintiles of CERAD WLT scores showed significant positive associations with log-transformed sodium levels (Immediate recall (IR) β = 4.25 (SE = 1.83, p-value 0.027); Delayed recall (DR) β = 6.54 (SE = 1.82, p-value 0.001)). Compared to normal sodium levels, hyponatremia was significantly associated with lower CERAD WLT-IR (β = -0.34, SE = 0.15, p-value 0.035) and CERAD WLT-DR scores (β -0.48, SE = 0.10, p-value < 0.001) and showed borderline significance with AFT scores (β = = -0.38, SE = 0.19, p-value 0.052). Hypernatremia did not show any significant relationships with cognitive test scores, compared to normal sodium levels.

Conclusions: Our cross-sectional study showed that lower sodium levels were associated with cognitive change, especially regarding memory and executive function.