Effects of a Novel Contextual Just-In-Time Mobile App Intervention (LowSalt4Life) on Sodium Intake in Adults With Hypertension: Pilot Randomized Controlled Trial

Background High dietary sodium intake is a significant public health problem in the United States. High sodium consumption is associated with high blood pressure and high risk of cardiovascular disease. Objective The aim of this study was to evaluate the effect of a just-in-time adaptive mobile app intervention, namely, LowSalt4Life, on reducing sodium intake in adults with hypertension. Methods In this study, 50 participants aged ≥18 years who were under treatment for hypertension were randomized (1:1, stratified by gender) into 2 groups, namely, the App group (LowSalt4Life intervention) and the No App group (usual dietary advice) in a single-center, prospective, open-label randomized controlled trial for 8 weeks. The primary endpoint was the change in the 24-hour urinary sodium excretion estimated from spot urine by using the Kawasaki equation, which was analyzed using unpaired two-sided t tests. Secondary outcomes included the change in the sodium intake measured by the food frequency questionnaire (FFQ), the 24-hour urinary sodium excretion, blood pressure levels, and the self-reported confidence in following a low-sodium diet. Results From baseline to week 8, there was a significant reduction in the Kawasaki-estimated 24-hour urinary sodium excretion calculated from spot urine in the App group compared to that in the No App group (–462 [SD 1220] mg vs 381 [SD 1460] mg, respectively; P=.03). The change in the 24-hour urinary sodium excretion was –637 (SD 1524) mg in the App group and –322 (SD 1485) mg in the No App group (P=.47). The changes in the estimated sodium intake as measured by 24-hour dietary recall and by FFQ in the App group were –1537 (SD 2693) mg and –1553 (SD 1764) mg while those in the No App group were –233 (SD 2150) mg and –515 (SD 1081) mg, respectively (P=.07 and P=.01, respectively). The systolic blood pressure change from baseline to week 8 in the App group was –7.5 mmHg while that in the No App group was –0.7 mmHg (P=.12), but the self-confidence in following a low-sodium diet was not significantly different between the 2 groups. Conclusions This study shows that a contextual just-in-time mobile app intervention resulted in a greater reduction in the dietary sodium intake in adults with hypertension than that in the control group over a 8-week period, as measured by the estimated 24-hour urinary sodium excretion from spot urine and FFQ. The intervention group did not show a significant difference from the control group in the self-confidence in following a low sodium diet and in the 24-hour urinary sodium excretion or dietary intake of sodium as measured by the 24-hour dietary recall. A larger clinical trial is warranted to further elucidate the effects of the LowSalt4Life intervention on sodium intake and blood pressure levels in adults with hypertension. Trial Registration ClinicalTrials.gov NCT03099343; https://clinicaltrials.gov/ct2/show/NCT03099343 International Registered Report Identifier (IRRID) RR2-10.2196/11282