SaltSwitch, a smartphone application to promote lower-salt food choices for patients with cardiovascular disease: 10-week effect

Abstract

Background: Cardiovascular disease (CVD) is the leading cause of mortality in New Zealand (NZ) and worldwide. Annually in NZ CVD accounts for ~17.5% (~167,000) of early deaths. Healthy diet plays a key role in the primary and secondary prevention of CVD. However, current methods for promoting healthy eating via cardiac rehabilitation programmes are costly and not scalable. SaltSwitch, a smartphone application (app), helps people identify lower-salt foods when shopping, and could potentially reduce their CVD risk. Objective: To explore the 10-week effect of the SaltSwitch app on the salt content of packaged food purchases for adults with CVD. Methods: A systematic review was conducted of randomised controlled trials (RCTs) of mobile health (mHealth) interventions for promoting healthy eating. Subsequently an exploratory sub-study was undertaken, set within the framework of a two-arm, parallel, RCT. The RCT (n=300; 2-weeks baseline, 4-weeks intervention) includes adults’ aged 40 years and older with CVD and their main household shopper, who are randomised to receive either the SaltSwitch app, or usual care. Substudy participants remained enrolled in the RCT for a further six weeks to examine the longer-term effects of the app. The primary outcome was salt content (g/MJ) of household food purchases after 10 weeks intervention (assessed using till receipt data). Secondary outcomes included: household purchases of saturated fat and energy, food purchase expenditure, and systolic blood pressure (BP) and 24-hour urinary sodium of participants with CVD. Results: Twelve RCTs (n=2018 participants), published: 2008-2014, were included in the review, which highlighted the insufficient amount of high-quality evidence on mHealth interventions for healthy eating, and the relevance of smartphone technology for future research. The sub-study (n=25; 13 intervention & 12 control), found no significant between-group differences in mean salt purchases (0.38g/MJ; p=0.120) after 10 weeks intervention. However, there was a trend toward decreases in mean urinary sodium (-296.13mg; p=0.309) and mean systolic BP (-12.14mmHg; p=0.73) for the intervention group. Conclusion: A larger RCT is required to evaluate the longer-term effectiveness of SaltSwitch for reducing salt purchases for patients with CVD. Missing data should be minimised and objective measures of salt intake (such as 24-hour urinary sodium) used.