VA|PREVENTION: Randomized Controlled Trial of a Person-Centred Digital Intervention to Prevent Diabetes in High-Risk Adults

The measurement of WC will be conducted using a standardized procedure (NIH, 1994; Pimenta et al., 2015; Ross et al., 2020) with an inelastic metallic anthropometric tape. The measurement of WC will be repeated 2 times, and if the second differed more than 1 cm from the first measurement, a third measurement will be carried out. We always considered the result obtained in the second measurement unless a third measurement is carried out. If a third measurement is taken, we will consider the mode or, if mode was absent, the median value of all 3 measurements.

FINDRISC risk score, is a validated tool for identifying individuals at high risk of developing T2DM. It incorporates various risk factors, including age, BMI, WC, and lifestyle habits (Lindström & Tuomilehto, 2003). Evaluating changes in FINDRISC categories allows for the assessment of the intervention's impact on overall diabetes risk, offering a comprehensive view of risk factor modification (WHO, 2020). FINDRISC risk score categories allow a maximum score of 26 points and classifies individuals into risk levels: low (< 7 points); mildly moderate (between 7 and 11 points); moderate (12-14 points); high (15-20 points) and very high (more than 20 points) (Dantas, 2017; Lindström & Tuomilehto, 2003).

Body weight will be measured using a digital scale that is pre-calibrated and placed on a flat, firm surface, with participants barefoot and wearing only light clothing without accessories. Body height will be measured as the highest point of the cranium (vertex) and the horizontal surface where the individual's feet are standing, in an upright position, using a stadiometer, following a standard protocol (Gordon, Chumlea and Roche, 1988). Body mass index will be calculated using body weight (in kilograms) divided by body height squared (in meters). The measurement of body weight and height will be repeated 2 times, and if the second differed more then 0.5 kg (for weight) or 1.0 cm (for height) from the first measurement, a third measurement will be carried out. We always considered the result obtained in the second measurement unless a third measurement is carried out. When a third measurement is taken, we will consider the mode or, if mode was absent, the median value of all 3.

Change in dietary behaviours will be assessed through MEDAS questionnaire. This questionnaire includes 14 items that evaluate the intake of key components of the Mediterranean diet. This is a validated tool widely used in research to assess adherence to the Mediterranean diet, which is strongly associated with reduced risk of type 2 diabetes (Martínez-González et al., 2012).

Change in dietary behaviours will be assessed through MEDAS questionnaire. This questionnaire includes 14 items that evaluate the intake of key components of the Mediterranean diet. This is a validated tool widely used in research to assess adherence to the Mediterranean diet, which is strongly associated with reduced risk of type 2 diabetes (Martínez-González et al., 2012).

Health-related quality of life will be assessed using the EQ-5D-5L questionnaire. This instrument evaluates five dimensions of health: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. The EQ-5D-5L is widely accepted in clinical research and is considered a reliable measure of health outcomes over time (Herdman et al., 2011).

Adoption will be assessed via rates and retention, based on data collected by user and second users' interactions with the VA|PREVENTION web app. This includes:

• Number of complete interactions with Ema for physical activity and dietary behaviours over the intervention period;
• Number of complete topics answered in the educational menus;
• Number of visits to the dashboard: (i) educative menus usage data ; (ii) self-monitoring and goal progress features; and (iii) feature showing the number of interactions with Ema;
• Length of use of: i) interactions with Ema; ii) Educative Menus; and iii) Dashboard for physical activity and dietary behaviours;
• Frequency of use of: i) interactions with Ema; ii) Educative Menus; and iii) Dashboard for physical activity and dietary behaviours
• Number of secondary users that access the dashboard
• Number of visits of secondary users to the dashboard;

The acceptability, appropriateness, and feasibility of the VA|PREVENTION web app will be assessed through the evaluation of:

• Acceptability, Appropriateness and Feasibility questionnaire responded by participants/users, secondary users and managers; Each section of the questionnaire has 4 items, responded on a 5-point likert scale, ranging from completely disagree to completely agree.
• Qualitative data from interviews with primary and secondary users.
• Qualitative date from interviews with managers of Primary Care Units and Community pharmacies; These will be telephone interviews, and thematic saturation will be used to determine the size of the samples with a minimum of 20 interviews planned for primary users, and a minimum of 10 participants for each of the remaining samples is envisaged.

Cost-effectiveness of the web app will be assessed through Incremental Cost-Effectiveness Ratio (ICER). ICER represent the ratio of the difference in costs and the difference in health outcomes. ICERs will be calculated for the comparison of the web app intervention with control group.

The primary ICER will be computed as cost per QALY derived using utility values calculated from the EQ-5D-5L instrument. In addition, ICERs can also be reported for the relation with other secondary outcomes, such as cost per cm reduction in waist circumference, or cost per point reduction in FINDRISC risk score.

The cost-effectiveness analysis will adopt a healthcare payer perspective.

The assessment of adverse events and software issues will focus on the identification and reporting of both serious and non-serious adverse events, as well as any deficiencies related to the investigational digital intervention. Continuous monitoring of adverse events is crucial to safeguard participant safety and maintain the integrity of the study's outcomes.