The LETHE pilot trial is a 24-month multicentre parallel-group randomised controlled trial conducted in Finland (Finnish Institute for Health and Welfare, THL), Austria (Medical University of Vienna, MUW), Sweden (Karolinska Institute, KI), and Italy (University of Perugia, UPG). LETHE is an academic-led trial (funded by EU Commission) where all four clinical centers are jointly and equally responsible for the planning and conduct of the trial.

The recruitment goal is 160 participants (40 per country). Participants will be recruited e.g., through public announcements or advertisements (newspaper, social media) and at the local study centres. Interested individuals will first be pre-screened to check the key inclusion criteria related to e.g., age, digital skills and readiness, and risk factor profile (CAIDE dementia risk score). Persons who appear to meet the inclusion criteria (and no reasons for exclusion have arisen) are then invited for the actual screening assessment visit (organised remotely or in-person) where the eligibility criteria are checked in detail (including cognition). Exclusion criteria are assessed by a physician (for those who meet the inclusion criteria). Eligible individuals are invited to the baseline visit at the study centre. After completing all baseline assessments, participants are randomised in 1:1 ratio to the intervention group (structured ICT-assisted multimodal lifestyle intervention) and control group (self-guided multimodal lifestyle intervention). Randomisation will be balanced across sites.

At the beginning of the study, all participants receive an Android smartphone (unless they have already a compatible phone which they prefer to use), first with a simplified version of the LETHE App installed where participants can complete a set of outcome assessment questionnaires (e.g., lifestyle-related). After randomisation, a visit is booked to hand out the Fitbit smartwatch (different versions for the intervention and control groups) and install the full study version of the App (also different for the different groups). The App and the smartwatch are used for both active and passive data collection throughout the trial, and to support the intervention delivery. The intervention group will be offered a structured and tailored multimodal lifestyle programme (based on the FINGER model) including regular in-person (face-to-face and remote) counselling and sessions led by professionals, as well as independent digital activities in the LETHE App. Sessions and activities are related to the following intervention components: physical activity, nutrition, cognitive activity, vascular risk management and monitoring, social interaction, sleep, and relaxation/stress management. Recommendations and plans are tailored. The LETHE App, which has been designed by the LETHE consortium for this project, has features such as e.g., a cognitive training program, on-demand exercise videos, calendar to schedule activities, advice and educational material, group chat, and possibility to set and monitor goals and self-monitor risk factors such as e.g., blood pressure. Participants in the self-guided group are instructed to build their own lifestyle programme based on general health and lifestyle recommendations that they will receive at the main study visits. They will also have access to a simplified version of the LETHE App with static educational content about healthy lifestyle, but without any structured and scheduled activities, interactive features, or personalised content.

After baseline, all participants are invited to the study centre for three main study visits to collect outcome information, at month 6, 12, and 24. The outcome assessors are blinded to the group allocation and participants are not actively told to which group they were assigned. Data collection through the digital devices takes place continuously. The primary objective of the trial is to assess the feasibility of the digitally supported multimodal lifestyle intervention programme, i.e., assess retention rate (what proportion of participants completes the 24-month intervention period) and adherence to the intervention and engagement with the digital tools. Furthermore, changes in validated dementia risk scores (CAIDE, LIBRA) are assessed. Other objectives include testing the intervention effects on lifestyle and different risk factors of cognitive decline and dementia, cognitive performance, physical functioning, health-related quality of life, health literacy, and dementia-related fluid and imaging biomarkers. Participants' experiences of study participation and views on e.g., the usability and acceptability of the digital tools will also be explored (through interviews/focus groups).