School-based programme to reduce dietary salt intake and blood pressure amongst adolescents and their parents: a cluster-randomised controlled trial in rural and urban Malawi

1.BackgroundExcess dietary salt intake and high blood pressure are growing public health challenges in Africa, with limited evidence for effective interventions. We evaluated the effect of a school-based programme on salt intake and blood pressure of adolescents and their parents. MethodsWe conducted a cluster-randomised controlled trial with 26 primary schools in rural and urban Malawi. All pupils aged 11-14 years and their parents were eligible. The intervention comprised lessons and activities delivered over one school term promoting reduced salt intake. Co-primary outcomes were change in adolescent salt intake and systolic blood pressure (SBP) at 3-months. Secondary outcomes were change in adolescent diastolic blood pressure (DBP), adult salt intake, and adult blood pressure at 3-months; and change in blood pressure of all participants at 12-months. FindingsWe recruited 1968 participants between September 24th-October 13th 2019 and January 8th-24th 2020. Thirteen primary schools received the salt reduction programme (362 adolescents, 614 adults) and 13 the routine curriculum (362 adolescents, 596 adults). At baseline, mean urinary salt was 3{middle dot}9g/day (SD 2{middle dot}15) for adolescents and 4{middle dot}3g/day (SD 2{middle dot}50) for adults. Participation in the intervention was high, with overall compliance of 87% by adolescents. At 3-months, there was no significant difference in change in adolescent salt intake (-0{middle dot}17g/day, 95% CI -0{middle dot}63-0{middle dot}29) or adolescent SBP (0{middle dot}59mmHg, -1{middle dot}80-2{middle dot}97). There was also no significant difference in change in adult salt intake, or blood pressure at 3 or 12 months, except adolescent SBP at 12-months. InterpretationA school-based salt reduction intervention was feasible and had high levels of engagement, but did not reduce salt intake or blood pressure of adolescents and adults over a 3-month period. Longer term implementation, complemented by broader strategy and policy engagement, may be needed for school-based approaches to achieve reductions in dietary salt and blood pressure. FundingMedical Research Council RegistrationISRCTN13909759 2. RESEARCH IN CONTEXT Evidence before this studyO_LIDespite evidence that population-level dietary salt (sodium chloride) intake in Africa exceeds global recommendations, rigorous evidence for effective public-health strategies to address this are lacking. School-based approaches are widely used in Africa for the delivery of preventive health services, and may present a practical and efficient platform for addressing excess dietary salt intake. C_LIO_LIA trial previously conducted in urban China demonstrated the feasibility of reducing salt intake amongst school-age children, but was conducted in a setting of relatively high excess salt intake and a better-resourced education system. Previous studies in Africa have demonstrated the feasibility and effectiveness of school-children as health messengers within their household, but this approach has not been evaluated for non-communicable diseases. C_LI Added value of this studyO_LIWe report the first randomised controlled trial of a school-based salt reduction programme to be conducted in Africa; and the first in a setting that is low-income, rural, or of moderate excess salt intake. Study strengths include recruitment across both rural and urban settings, enhancing generalisability, and the use of 24-hour urine collection, providing robust assessment of salt consumption. C_LIO_LIAt baseline, we observed lower estimates of dietary salt intake than previously estimated through spot urine samples, equating to 27% of child and 33% of adult participants consuming dietary salt in excess of WHO recommendations. After 3-months, the average salt intake of school-children or adults who received the intervention did not significantly reduce overall after intervention implementation for one school term, compared to those who continued to receive the routine school curriculum (control). C_LI Implications of all the available evidenceO_LISalt-reduction strategies that leverage cross-sectoral partnerships, engaging education, health, and community actors, present a pragmatic approach to addressing excess salt intake in Africa. Our results demonstrate the feasibility of implementing such interventions within schools to reach both children and adults. C_LIO_LIWhile we did not observe significant reductions in salt intake, this may reflect the short implementation period and moderate baseline salt intakes in our study population. School-based interventions may need to be sustained over multiple years to achieve meaningful reductions in dietary salt intake, combined with complementary strategies including community engagement, school meal policies, and food environment modifications. C_LIO_LIFuture research should consider evaluation of broader school-based interventions that are implemented over extended periods, embedded within comprehensive population-level salt reduction strategies. C_LI