Regional effect of population-based programs promoting salt reduction and potassium intake in Hokkaido: a post hoc analysis of the PoSPIP

Abstract The Population-based Sodium/Potassium Improvement Program is a nonrandomized population-based intervention implemented by the Japanese Society of Hypertension across multiple municipalities and workplaces in Japan. This post hoc regional analysis focused on two municipalities in Hokkaido—namely, Higashikagura, which received standard support, and Mashike, which received intensive support consisting of on-site urinary sodium-to-potassium (Na/K) ratio measurement, immediate feedback, repeated health guidance, and food-environment improvement. A total of 431 participants who underwent annual health checkups in 2021 and 2022 and had urinary Na/K ratio data at both time points (standard support group, n = 218; intensive support group, n = 213) were included. One-year changes in the urinary Na/K ratio, estimated salt and potassium intakes, blood pressure (BP), and other clinical measures were compared between the groups using multivariable linear regression. The proportion of participants achieving urinary Na/K ratio targets increased in the intensive support group. A significant group-by-time interaction was observed for the <2 threshold (OR 2.62, 95% CI: 1.25–5.50), but not for the <4 threshold. After adjustment for covariates, estimated salt intake decreased more in the intensive support group than in the standard support group (adjusted group difference: −0.53 g/day, 95% confidence interval: −0.95 to −0.12). Changes in the urinary Na/K ratio, estimated potassium intake, and systolic and diastolic BP did not significantly differ between the groups. Intensive support incorporating urinary Na/K ratio measurement, immediate feedback, and repeated multidisciplinary guidance may promote salt reduction in local community settings.