Using mobile technology to support lower-salt food choices for people with cardiovascular disease: protocol for the SaltSwitch randomized controlled trial

Background: Cardiovascular disease (CVD) is the leading cause of early death worldwide, responsible for an estimated 29% of all global deaths. Reducing salt intake lowers blood pressure and risk of secondary cardiac events. However, identifying low salt foods can be challenging. SaltSwitch is a simple smartphone application (app) that enables shoppers to scan the barcode of packaged foods and receive an immediate, interpretive, traffic light nutrition label on the screen, along with suggestions for healthier lower-salt alternatives. A growing body of evidence suggests mobile technologies can support healthy behaviour change. However, robust evidence for the impact of smartphone interventions is lacking. This manuscript outlines the rationale and methods for a randomized controlled trial designed to determine the effectiveness of SaltSwitch in supporting people with CVD to make lower-salt food choices. Design/Methods: A 6-week, two-arm, parallel, randomized controlled trial is being undertaken in New Zealand (2 weeks baseline and 4 weeks intervention). Three hundred adults aged 40 years and older with CVD and their main household shoppers are recruited from research lists, cardiac rehabilitation clinics, and communities in Auckland. Participants are randomized to receive either the SaltSwitch smartphone app or no intervention (control). Randomisation is stratified by ethnicity and age. The primary outcome is the salt content of household food purchases. Secondary outcomes are the saturated fat and energy content of household food purchases, household food expenditure, use and acceptability of the SaltSwitch app by shoppers, and urinary sodium and blood pressure of participants with CVD. Ambulatory blood pressure and potential longer-term impact (12 weeks) of SaltSwitch will be assessed in sub-studies (n ~ 40 and n ~ 20, respectively). Household purchases of salt and other nutrients will be assessed using till receipt data electronically linked with branded food composition data. Discussion: The results of the SaltSwitch trial will determine the effectiveness, use and acceptability of a smartphone application to support lower salt food choices and secondary prevention of CVD. Trial registration: ACTRN12614000206628. Registered 30 March 2014