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.