Independent and joint associations of urinary potassium excretion with cardiovascular death: a national population-based cohort study

Abstract Background Elevated potassium excretion is associated with lower blood pressure, as well as reduced risks of cardiovascular disease (CVD) death. However, the impact of varied sodium levels on this association remains a topic of debate, and the mediators of this association besides blood pressure remain uncertain. Purpose To examine the joint association of potassium and sodium with CVD mortality risk, and to identify potential mediating factors of this association. Methods Based on the ChinaHEART (China Health Evaluation And risk Reduction through nationwide Teamwork) project, participants aged 35-75 from 239 sites across all 31 provinces in the mainland of China were recruited from November 2014 to December 2022. We collected spot urine samples from participants and estimated 24-hour sodium and potassium excretion using the Kawasaki formula. Death records were captured through data linkage with the National Mortality Surveillance System and Vital Registration. Multiple regressions were used to analyze the association between potassium excretion and CVD death, as well as to examine the addictive interaction of potassium and sodium. Results This study included 270,991 participants with a mean age of 55.8±9.8 years, and 60.5% of them were female. The mean potassium excretion was 54.36±12.58 mmol/d , which was higher in males and people living in the north. Findings revealed a positive correlation between low urinary potassium levels and CVD death , and the lowest adjusted hazard rate for CVD mortality was 0.65 (95% CI: 0.58-0.73) in the group with the highest potassium excretion (i.e. ≥64.27 mmol/d) compared with the reference group (<43.79 mmol/d), after adjusting for sociodemographic characteristics, medical histories, and lifestyles. Age modified the association between potassium excretion and risk of CVD death (P for interaction=0.031). In addition to systolic blood pressure (16.6%), heart rate (2.2%) also served as the significant mediator between urinary potassium excretion and CVD death. The relative excess risk of interaction (RERI) of lower potassium excretion and lower sodium was significantly positive (RERI=0.22, 95% CI: 0.02-0.42), which implied the synergy effect. Conclusion Potassium intake in the Chinese population is evidently lower than the guideline recommendations, and increasing potassium intake, especially in the population aged <65 years, may reduce the risk and burden of cardiovascular and other diseases. Moreover, when sodium intake is insufficient, supplementation with both sodium and potassium salt can achieve greater health benefits.Graphic abstract