ABSTRACT
Background
Excess dietary sodium intake is a major contributor to hypertension (HTN) and cardiovascular disease in the U.S., yet most Americans exceed recommended sodium intake levels. Despite the established benefits of sodium reduction, behavioral adherence remains a challenge. Just-in-time adaptive interventions (JITAIs) provide a novel mobile health (mHealth) strategy to support low-sodium choices in real-time at restaurants and grocery stores.
Methods
LowSalt4Life 2 is a 6-month randomized controlled trial evaluating a mobile application-based sodium-focused JITAI among adults with HTN. In phase one, participants were randomized 1:1 to either the LowSalt4Life app with JITAI (App+JITAI) or the app alone. At 2 months, the App+JITAI group was re-randomized to either continue with the standard JITAI or receive a personalized JITAI (pJITAI) informed by reinforcement learning based on prior engagement. The primary outcome was change in systolic blood pressure (SBP) at 2 months. Secondary outcomes included changes in BP medication, dietary sodium intake, and engagement metrics.
Results
As of October 2025, 410 participants had been enrolled and completed follow-up. The trial’s final results are anticipated in Spring 2025. Primary analysis focuses on the change in SBP between the App+JITAI and App-only groups, as well as the added value of personalization in the second study phase.
Conclusions
LowSalt4Life 2 tests a scalable, context-aware digital intervention designed to reduce dietary sodium and improve BP management. By personalizing engagement based on user behavior, this study seeks to advance mHealth strategies for HTN self-management and inform future interventions targeting dietary behaviors in real-world settings.
Background
High dietary sodium intake is a significant public health concern in the U.S., given its association with high blood pressure (BP). In a meta-analysis of 177,025 patients, higher sodium consumption was associated with a greater risk of stroke and a trend toward greater cardiovascular risk due to its association with hypertension (HTN). Based on 2005 estimates, high dietary sodium is responsible for 102,000 deaths annually. Current federal guidelines recommend a daily sodium intake of less than 2,300 milligrams (mg), with a further reduction to 1,500 mg for individuals aged 51 and older, as well as for anyone of any age who is African American or has hypertension (HTN), diabetes, or chronic kidney disease. Yet, the average sodium intake for all Americans age 2 years and older is approximately 3,400 mg daily. Conversely, lower sodium intake has been shown to reduce both BP and prevent atherosclerotic cardiovascular diseases (ASCVD). In an analysis of the Trials of Hypertension Prevention (TOHP), participants randomized to the low-sodium interventions had a 25% lower long-term risk of cardiovascular disease. The sodium-restricted Dietary Approach to Stop Hypertension (DASH) eating plan reduced systolic BP (SBP) by 7.1 mm Hg in adults without HTN and 11.5 mm Hg in adults with HTN. In England, the National Health Survey showed a 1,400 mg-per-day reduction in dietary sodium intake over 8 years, which coincided with a nationwide decline in cardiovascular mortality. Despite widespread awareness of the risks associated with high dietary sodium intake, clinicians continue to face challenges in engaging patients with lifestyle-based treatments that can reverse these trends and encourage ongoing self-management and long-term adherence to low-sodium diets.
Patients often require assistance in grocery stores and restaurants to follow a low-sodium diet. Over half of all Americans consume one to 3 restaurant meals per week, and 23% consume 4 or more restaurant meals per week. , The use of pre-packaged foods in home meal preparation has also increased substantially in recent years. Restaurants and grocery stores are prime targets for intervention, with approximately 77% of the average U.S. diet’s sodium intake coming from processed and restaurant foods. , In a recent study on consumer knowledge of sodium intake and food labeling, only half of over 400 grocery store shoppers could accurately use sodium label information to choose low-sodium food options. In a qualitative study using a focus group that included cardiovascular patients, 3 main themes emerged for nonadherence to a low-sodium diet: lack of knowledge, interference with socialization, and lack of food selections. Many focus group participants needed more detailed information about a low-sodium diet. They expressed frustration in eating at restaurants, stating that eating out was an obstacle to adhering to their prescribed diet. Finally, patients cited limited choice and poor taste as barriers to consuming low-sodium food
We developed a mobile application-based just-in-time adaptive intervention (JITAI) named LowSalt4Life to help patients reduce sodium intake. JITAIs represent a new category of mHealth interventions designed to meet the evolving needs of individuals by delivering support at times when it is most likely to be effective. Broadly adopted from behavior change theory, JITAIs are motivated by rapidly identifying vulnerable states using contextual data and delivering tailored interventions to mitigate or prevent behaviors with potentially adverse health consequences. JITAIs have shown efficacy in multiple treatment domains, including smoking cessation, physical activity, alcohol abuse, and mental health treatment. ,, The LowSalt4Life dietary sodium intervention delivers contextual push notifications linked to tailored in-app content, promoting lower-sodium alternatives when participants are most vulnerable, at grocery stores and restaurants. This intervention was initially studied to determine the effects on sodium intake. , Fifty participants were randomized 1:1, stratified by gender, to receive the mobile application with JITAI (App+JITAI) or usual care (UC) for 8 weeks in the LowSalt4Life 1 trial. Those randomized to the intervention experienced a greater reduction in sodium intake compared to the control group. Systolic blood pressure was also lower in the intervention group than in the control group over the 8 weeks, but the study was not powered to detect this difference.
Objectives
This manuscript describes the rationale and design of the LowSalt4Life 2 clinical trial. This study was designed to determine the effect of the LowSalt4Life dietary sodium-focused JITAI on SBP over 2 months in patients with HTN. The second objective is to identify the dietary mediators of the intervention’s effect on blood pressure (BP). Our third aim is to determine the long-term effect of the JITAI on SBP change after we personalize the intervention based on patient engagement with push notifications at grocery stores and restaurants.
Methods
Study design
This study is a 6-month, sequential, prospective, randomized, controlled clinical trial in patients with HTN. In the first step, participants were randomized to either the mobile application with JITAI (App+JITAI) or the mobile application alone (App alone) in a 1:1 ratio and were followed for 2 months. The randomization table was created by the statistician using block randomization stratified by sex, and then provided to software developers to integrate into the mobile apps. This 2-month trial will determine the efficacy of the dietary sodium JITAI on BP over time when compared with the App alone and identify the dietary mediators of the intervention’s effect on BP. In the second step, the App+JITAI group will be further randomized in a 1:1 ratio to either App+JITAI or App+personalized JITAI (pJITAI) to evaluate the long-term effects of personalized JITAI on BP over time through enhanced patient engagement. All participants received a cellular-enabled BP cuff (BPM Connect Pro, Withings, Inc.) and scale (Body Pro, Withings, Inc.), and could view their blood pressure and weight in the LowSalt4Life app. They did not use the Withings app. Participants in the App alone group did not receive notifications or in-app education about dietary sodium intake. The University of Michigan IRB approved the trial (HUM00210954). The National Heart, Lung, and Blood Institute (NHLBI) funded the trial, and it is available on ClinicalTrials.gov (NCT05396001). An overview of the study design is located in Figure 1 .
The LowSalt4Life study design.
Subject eligibility
All participant inclusion and exclusion criteria are listed in Table 1 .
Table 1
Patient inclusion and exclusion criteria
| Inclusion criteria |
|
| Exclusion criteria |
|
Intervention
All participants will receive the LowSalt4Life mobile application, which was available for both iOS and Android devices. The mobile application includes a JITAI (App+JITAI) that is turned on or off based on the randomization assignment for the clinical trial. The dietary sodium JITAI facilitates lower-sodium choices at restaurants and grocery stores by using tailored and contextual push notifications. , Users complete an initial sodium screener to identify their top sodium-containing foods and select lower-sodium alternatives to those foods. Push notifications were tailored to the participants’ confidence in following a low-sodium diet and the type of location (grocery store or restaurant). Participants in the App+JITAI group are randomized to either an optimized version of JITAI or the standard version of JITAI after a 2-month period.
The JITAI provides just-in-time contextual information using an internet-based location service, NumberEight, to determine when a participant arrives at a grocery store or restaurant. NumberEight uses artificial intelligence algorithms that analyze the changes in mobile phone sensors, including Wi-Fi, Bluetooth, accelerometer, gyroscope, magnetometer, and GPS. The artificial intelligence algorithm understands the user’s pattern of phone sensor use, recognizes their present context, and predicts future activity. These predictions, generated by NumberEight, alert the mobile application that the user is at a grocery store or restaurant.
Nutritionix is a company that aggregates nutrition data for over 690,000 grocery store items and 149,000 restaurant menu items from over 790 national chains. It also provides the Universal Product Code (UPC) for grocery items, enabling the scanning of products with labels and the ability to receive standard nutritional facts for common foods without a label. The Nutritionix data is used to access the most up-to-date food information when the user interacts with the app. The crucial advantage of using Nutritionix is the ability to tailor the data elements presented and display items based on their sodium content.
Once the app determines the user’s context, they receive a tailored message based on their location (e.g., grocery store or restaurant). Tapping on a push notification at a grocery store directs the user to a page where they can scan the UPC on food packaging or conduct a text search within the grocery store. As the participant scans the food item, the UPC will be linked to the nutritional facts for the product. Tapping on a push notification at a restaurant will direct the user to a page with dietary information about that restaurant, based on their GPS location. The user can also find nutritional information in the app at any time, regardless of context or location. This also allows participants to check the foods in their homes and receive feedback on their choices. The mobile app provides feedback on the food’s sodium content using a traffic light signal— red, yellow, and green— to show participants at a glance whether a product is high, medium, or low in sodium. Figure 2 shows screenshots of several pages within the LowSalt4Life app.
LowSalt4Life app screenshots.
At 2 months, participants in the intervention arm will be randomized to a personalized version of the JITAI or to continue with the baseline version of the JITAI for the remaining 4 months. The personalized version of the JITAI will be based on the participant’s engagement with push notifications. During the first 2 months, push notifications will be sent to individuals 80% of the time, and metrics will be collected for each push notification. These metrics include patient characteristics, type of push notification (grocery store, restaurant), other contextual factors (time of day, weather), and whether the user acted on the push notification. An algorithm will be constructed using reinforcement learning. The algorithm will “learn” which metrics lead to participant action in the first 2 months. To maximize participant engagement, the personalized JITAI will alter the number of push notifications sent for the remainder of the study in that randomized arm. Participants in the control group will remain in the control group for the entire 6 months.
Study endpoints
The primary outcome of the clinical trial is the change in SBP over 2 months. Blood pressure was measured at home using a cellular-enabled BP cuff, BPM Connect Pro (Withings, Inc.). At baseline, participants were instructed to adjust the cuff settings to measure 3 consecutive blood pressure (BP) measurements at each time point. The 3 automated BPs are taken one minute apart. The BP cuff then provides an average of those 3 measurements each time the participant takes their blood pressure. All participants were reminded to take their blood pressure readings every 2 weeks during the study. Secondary outcomes in the clinical trial include the percentage of participants achieving their goal BP and changes in BP medications. BP control was measured by the number of participants within a goal BP, measured every 2 months, and the changes in BP medications. Each participant’s goal BP was <130/80 mm Hg to analyze this outcome. BP medication changes were defined as any change to the participant’s BP medications (drug or dose) during the follow-up period. These will be further categorized as an increase or decrease in BP medications. Change in body weight is another secondary outcome of the trial. Weight was measured at home using a cellular-enabled scale, Body Pro (Withings, Inc.). Participants were instructed to take measurements every 2 weeks over a 6-month period.
Changes in dietary nutrient intake, including sodium, potassium, and caloric intake, are secondary outcomes in this trial. Dietary sodium intake was measured using the 110-question Block FFQ (version 2014.1) and the sodium screener survey (NutritionQuest, LLC) at baseline, 2 months, and 6 months. The Block FFQ is an electronically self-administered tool that records commonly consumed foods to estimate nutrient and energy intake. The instrument was developed based on the National Health and Nutrition Examination Survey (NHANES) nutrition data and includes adjustment questions to enhance accuracy in assessing macro- and micronutrient food intake. Analysis of dietary nutrient content is performed with standardized software. The Block Sodium Screener, a survey tool consisting of 32 response items, was administered electronically by each study participant. It assesses participants’ eating habits over the past month, asking about the frequency and quantity of specific foods they eat. This short-form survey provides an estimate of dietary sodium intake based on the answers to the questionnaire. Table 2 outlines a schedule of activities for the outcomes assessed in the clinical trial.
Table 2
Schedule of activities
| Procedure | Screening and enrollment | Baseline (+30 days) | Week 2 (+/- 5 days) |
Every 2 weeks
(+/- 7 days) |
2 months
(+/- 7 days) |
4 months
(+/- 7 days) |
6 months
(+/- 28 days) |
|---|---|---|---|---|---|---|---|
| Informed consent | X | ||||||
| Inclusion/exclusion | X | ||||||
| App training & application-specific questionnaires | X | ||||||
| Demographics | X | ||||||
| Medical history | X | ||||||
| Randomization | X | ||||||
| Blood pressure/weight | X | X | |||||
| Food Frequency Questionnaire | X | X | X | ||||
| Sodium screener | X | X | X | ||||
| Follow-up call or email: Tech check | X | ||||||
| Follow-up call or email & EHR review | X | X | X | ||||
| Final status | X |
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