{ "background": "Excessive dietary sodium is a major modifiable risk factor for hypertension, a leading cause of morbidity and mortality in South Africa. Urban township populations face specific environmental and socioeconomic barriers to reducing salt intake. Mobile health (mHealth) interventions using behavioural nudges offer a scalable, low-cost strategy, but their effectiveness in this context requires robust evaluation.", "purpose and objectives": "This protocol describes a randomised controlled trial to assess the effectiveness of a mobile phone-based behavioural nudge intervention, compared to usual care, in reducing dietary sodium intake among hypertensive adults in Khayelitsha. The primary objective is to determine the intervention's effect on 24-hour urinary sodium excretion. Secondary objectives include effects on blood pressure, dietary knowledge, and salt-related behaviours.", "methodology": "A two-arm, single-blind, parallel-group RCT will enrol 300 hypertensive adults. Participants will be randomised (1:1) to receive either a 12-week mHealth intervention (daily SMS nudges and weekly interactive voice messages promoting salt reduction) or usual care. The primary outcome is change in 24-hour urinary sodium excretion from baseline to 12 weeks. Secondary outcomes include office and home blood pressure measurements and questionnaire-assessed behaviours. Analysis will use an intention-to-treat approach. The primary analysis will employ a linear mixed-effects model: $Y{ij} = \\beta0 + \\beta1 Ti + \\beta2 Bi + uj + \\epsilon{ij}$, where $Y{ij}$ is the sodium excretion for participant $i$ at follow-up $j$, $Ti$ is the treatment indicator, $Bi$ is the baseline measurement, $uj$ is the random intercept, and $\\epsilon_{ij}$ is the error term. The treatment effect will be reported with a 95% confidence interval.", "findings": "As this is a protocol for a future study, no empirical findings are available. The anticipated primary result is a reduction in mean 24-hour urinary sodium excretion of