Association between spot urinary sodium-to-potassium ratio and blood pressure among Chinese adults aged 18-69 years: the SMASH study.

Background: Excessive sodium and low potassium intake are involved in the development of hypertension. Growing evidence showed that the sodium-to-potassium ratio (Na/K) was significantly associated with blood pressure (BP). However, studies on the dose-response relationship of spot urinary Na/K ratio with hypertension and BP in the general population are scarce, especially in the Chinese population. Materials and methods: Data from the post-intervention survey of the Shandong Ministry of Health Action on Salt and Hypertension (SMASH) project was analyzed. Associations between Na/K molar ratio and hypertension prevalence and between Na/K molar ratio and BP indices were analyzed using multivariable logistic and linear regression, respectively, followed by subgroup analysis and interaction analysis. The restricted cubic spline model was used to explore the dose-response relationship. Informed by existing literature, we adjusted for potential confounding factors, including temperature and renal function, to assess the association and dose-response relationship. Results: There was a non-linear positive association between Na/K and hypertension (OR:1.09, 95%CI: 1.08-1.11) and a linear positive association between Na/K and systolic BP, diastolic BP, and mean arterial pressure (β 0.53, 95%CI: 0.45-0.60; β 0.36, 95%CI: 0.31-0.41; and β 0.42, 95%CI: 0.36-0.47, respectively). The association was stronger in individuals with hypertension, female patients, those in the 50-59-year age group, and those who were obese. Environmental temperatures had little impact on associations. Conclusion: Our findings provide further evidence that the spot urinary Na/K ratio is a simple, useful, and convenient indicator for monitoring salt reduction and potassium increase, which could be used in clinical and public health practices.