Persistent effect of salt reduction in schoolchildren and their families: one-year follow-up after a randomised controlled trial

Objective: A previous 12-month randomised controlled trial (RCT) demonstrated the effectiveness of an application-based education program, conducted through schoolchildren, in reducing the salt intake and systolic blood pressure of their adult family members. This study aimed to assess whether the effect at 12 months persisted at 24 months. Design and method: As a follow-up survey of a cluster RCT with 54 schools randomly assigned to either the intervention or control group, all participants who completed the baseline survey were contacted again at 24 months, following a 12-month non-intervention period after the RCT. The primary outcome was the difference in salt intake change between the intervention and control groups at 24 months versus baseline and 12-month follow-up, measured by the mean two consecutive 24-hour urinary sodium excretions. The secondary outcome was the difference in blood pressure change. Results: At 24 months, 542 children and 974 adults were followed up, accounting for 91.6% and 82.3% of the participants, respectively. The mean salt intake in adults at baseline, 12 months and 24 months was 10.0 g/day (standard deviation 3.5), 8.9 g/day (standard deviation 3.2) and 9.4 g/day (standard deviation 3.5) in the intervention group and 10.0 g/day (standard deviation 3.6), 9.8 g/day (standard deviation 3.9) and 9.8 g/day (standard deviation 3.9) in the control group. The mean difference in salt intake change in adults between the intervention and control groups after adjusting for confounding factors is -0.38 g/day at 24 months versus baseline (95% confidence interval -0.81 to 0.05, P=0.086), and 0.45 g/day at 24 months versus 12 months (95% confidence interval 0.01 to 0.85, P=0.046). The mean difference in systolic blood pressure change after adjusting for confounding factors is -2.19 mm Hg (95% confidence interval -3.63 to -0.76, P=0.003) at 24 months versus baseline and -0.40 mm Hg (95% confidence interval -1.86 to 1.07, P=0.596) at 24 months versus 12 months. Conclusions: The effect of the education program on adults’ salt intake faded, but the systolic blood pressure lowering effect remained 12 months after the RCT. Continuous salt reduction education is recommended to maintain the effect.