Are changes in the urinary sodium-to-potassium ratio associated with changes in blood pressure in a healthy population with low urinary sodium-to-potassium ratios? Eight-year follow-up results from the KOBE Study

Little is known about the associations between changes in the urinary sodium-to-potassium (Na/K) ratio and blood pressure (BP) in healthy individuals. Using survey data, urinary data, and BP data from the KOBE Study, this longitudinal study aimed to assess the associations between changes in the urinary Na/K ratio and BP in a healthy Japanese population over an 8-year follow-up period. We analyzed 567 participants aged 40-74 years who did not initiate antihypertensive or cardiovascular disease treatment during follow-up. Changes in the spot urinary Na/K ratio and BP were calculated by subtracting the baseline values from the follow-up measurements, and their associations were examined using a multivariable linear regression analysis that adjusted for sex, age, body mass index, baseline Na/K ratio and BP, low-density lipoprotein, hemoglobin A1c, ethanol intake, smoking status, salt taste sensitivity, years of education, employment status, baseline survey season, and 8-year follow-up survey season. The study cohort had a mean spot urinary Na/K ratio of 2.1 at baseline. While BP increased significantly over the 8-year follow-up period, the urinary Na/K ratio remained unchanged. However, urinary Na/K ratio changes were positively associated with changes in systolic BP (β = 1.48, p = 0.001) and diastolic BP (β = 0.76, p = 0.004). In conclusion, increases in spot urinary Na/K ratios were predictive of long-term BP elevation in a healthy, normotensive population with near-optimal urinary Na/K ratios at baseline. These findings indicate that maintaining a low urinary Na/K ratio is important for BP control, even among healthy individuals.