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

Objectives To determine the importance of a decrease in serum sodium concentration within the normal range in elderly adults. Design Prospective cohort. Setting The Korean Longitudinal Study on Health and Aging. Participants Randomly selected, community-based elderly population with a corrected serum sodium level between 135.0 and 145.0 mEq/L (N = 949). Measurements Survival status was determined during 63.3 ± 16.6 months of follow-up. Results Participants were divided into corrected sodium groups as follows: 73 (7.7%) in Group 1 (sodium 135.0-138.0 mEq/L), 635 (66.9%) in Group 2 (sodium 138.1-142.0 mEq/L), and 241 (25.4%) in Group 3 (sodium 142.1.0-145.0 mEq/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 138.0 mEq/L or less and a corrected sodium level greater than 138.0 mEq/L had a better survival rate than those with a measured sodium level of 138.0 mEq/L or less and a corrected sodium level of 138.0 mEq/L or less. Conclusion 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.