Association Between Small Decrease in Serum Sodium Concentration within the Normal Range and All-Cause and Cardiovascular Mortality in Elderly Adults over 5Years.

Abstract

To determine the importance of a decrease in serum sodium concentration within the normal range in elderly adults. Prospective cohort. The Korean Longitudinal Study on Health and Aging. Randomly selected, community-based elderly population with a corrected serum sodium level between 135.0 and 145.0mEq/L (N=949). Survival status was determined during 63.3±16.6 months of follow-up. Participants were divided into corrected sodium groups as follows: 73 (7.7%) in Group 1 (sodium 135.0-138.0mEq/L), 635 (66.9%) in Group 2 (sodium 138.1-142.0mEq/L), and 241 (25.4%) in Group 3 (sodium 142.1.0-145.0mEq/L). There were 34 (46.6%) deaths in Group 1, 124 (19.5%) in Group 2, and 52 (21.6%) in Group 3 (P<.001). In a Cox proportional hazards analysis, a 2-mEq/L higher sodium level reduced the risk of death by 14.9% (95% confidence interval (CI)=0.1-27.4%, P=.048). Group 1 had risk of mortality that was 2.7 times as high as that of Group 2 (95% CI=1.76-4.11, P<.001). Participants with a measured sodium level of 138.0mEq/L or less and a corrected sodium level greater than 138.0mEq/L had a better survival rate than those with a measured sodium level of 138.0mEq/L or less and a corrected sodium level of 138.0mEq/L or less. A slightly lower serum sodium concentration within the normal range was a major risk factor for mortality in elderly adults. Sodium level corrected according to serum glucose concentration was a more meaningful risk factor than measured sodium level.