Effectiveness of an mHealth-Based School Sodium Reduction Scaling-Up Program in Three Chinese Cities: A Real-World Pre–Post Study Among Adults and Children

Objective: To systematically evaluate the impact of a school-based sodium reduction education program using mobile health (mHealth), known as EduSaltS, on salt-related knowledge, attitudes, practices (KAP) and sodium intake among adults and children during its real-world scaling-up and to examine geographic and population heterogeneity in its effects. Methods: A multi-center pragmatic pre–post study design was used. The EduSaltS program was implemented in three cities (Ganzhou in southern China, Zhenjiang in eastern China, and Qinhuangdao in northern China) between April 2022 and July 2024. Ten primary schools were selected from each city. Baseline and follow-up surveys were conducted approximately 12 months apart, aligned with the school calendar. Electronic questionnaires were used to collect baseline and post-intervention data on the primary outcome—salt-related KAP—from adults and children. In Ganzhou and Zhenjiang, 24 h urine collections were conducted to measure urinary sodium excretion. Results: A total of 721 adults and 770 children were included in the final analysis. After the intervention, the total KAP scores significantly increased in both adults and children across the three sites: by 8.7–10.0 points in adults and by 11.4–16.7 points in children (all p < 0.001). The changes in sodium intake showed significant heterogeneity. A significant decrease in urinary sodium was observed among adults in Ganzhou (−14.0 mmol/24 h, 95% CI: −26.1, −2.0, p = 0.022), corresponding to a reduction of 0.82 g in daily salt intake. No significant change was found among adults in Zhenjiang (adjusted difference: −0.7 mmol/24 h, 95% CI: −13.4 to 12.0, p = 0.912). In children, after the one-year intervention, urinary sodium excretion showed a significant increase from baseline to follow-up in both cities (Ganzhou: +12.9 mmol/24 h, p = 0.018; Zhenjiang: +14.0 mmol/24 h, p = 0.0002). Conclusions: The pre–post evaluation showed that the EduSaltS program was associated with significant improvements in salt-related knowledge across regions. Its effectiveness in reducing sodium intake, however, varied substantially by population and geographic location. The observed increase in children’s urinary sodium excretion may partly reflect normal childhood growth and the limitations of a pre–post design without a control group. Pragmatic randomized controlled trials are warranted to verify the effectiveness of such interventions in reducing sodium intake and blood pressure across diverse populations and settings.