Previous research has shown that a healthy lifestyle, including a balanced diet, physical and social activity, and management of vascular risk factors can support both cardiovascular and brain health. In a landmark Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER), a multimodal lifestyle programme had clear benefits on older adults' cognition, functioning, and quality of life. The LETHE study utilises novel technologies and digital tools to deliver an optimised and more personalised FINGER-type multimodal lifestyle intervention.

A total of 160 digitally skilled older adults (age 60-77) with risk factors for dementia but without substantial cognitive impairment will be recruited in Austria, Finland, Italy, and Sweden. Participants will be randomly assigned in a 1:1 ratio to the structured ICT-assisted multimodal lifestyle program (intervention group) or a self-guided lifestyle program (control group). Duration of the study and the intervention is 24 months. The multimodal lifestyle program covers the following domains: physical activity, nutrition, cognitive activity, vascular risk management, social interaction, sleep, and relaxation. The structured intervention program follows a hybrid model where regular in-person, individual and group-based intervention activities led by professionals are supported with activities in the LETHE mobile phone application. The self-guided (control) group receives relevant health advice and is recommended and encouraged to independently implement healthy lifestyle changes that are suitable and fit in with their daily routine. Control group will have access to a simplified version of the LETHE app without any structured, scheduled activities or personalized content.

The primary objective of the LETHE trial is to test the feasibility of a digitally supported multimodal lifestyle program (i.e., retention rate, adherence to intervention), and assess change in dementia risk based on validated risk scores (CAIDE, LIBRA). Other objectives include testing the intervention effects on lifestyle and risk factors, cognition, function, health-related quality of life, health literacy, physical functioning, and dementia-related biomarkers. To this aim, a range of personal, lifestyle, and health-related data will be collected both actively and passively with the help of digital devices. Attitudes towards digital tools and experiences of trial participation will also be explored.

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).

Inclusion Criteria:

• Age 60-77 years
• Cardiovascular Risk Factors, Aging and Incidence of Dementia (CAIDE) Risk Score ≥ 6 points
• Cognitive performance at the mean level or slightly lower than expected for age, assessed with Mini-Mental State Examination (MMSE) and the Consortium to Establish a registry for Alzheimer's Disease (CERAD) verbal learning test (word list learning/recall)
• Proficiency in the local language (German, Italian, Finnish or Swedish)
• Ability and willingness to use an Android smartphone, access to and ability to use the internet (digital readiness)
• Existing compatible smartphone (Android) or willingness to use a new Android smartphone provided from the study

Exclusion Criteria:

• Dementia or substantial cognitive impairment (e.g., memory clinic referral needed as judged by the study physician)
• Current or past use of medications for Alzheimer's disease or related diseases (e.g., cholinesterase inhibitors, memantine)
• Diminished decision-making capacity, not capable of consenting or completing study assessments, based on clinical judgement
• Other significant neurologic disease, including but not limited to Parkinson's disease, Huntington's disease, normal pressure hydrocephalus, brain tumor, progressive supranuclear palsy, seizure disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma with persistent neurologic sequelae or known structural brain abnormalities
• Any condition affecting safe engagement in the intervention, e.g., malignant disease, major depression, symptomatic cardiovascular disease, revascularisation within 1 year previously
• Severe loss of vision, hearing, or communicative ability; conditions preventing cooperation as judged by the study physician
• Concomitant participation in an interventional trial (unless this will not interfere with the LETHE trial based on study staff's judgement)

The LETHE consortium is open to requests from external researchers for data collected in this study. Applicants will be asked to submit a study protocol, including the research question, planned analysis, and data required. Data controllers will evaluate this plan (i.e., relevance of the research question, suitability of data, quality of proposed analyses, planned/ongoing LETHE analyses, and other matters) on a case-by-case basis and provide the data or reject the request. Shared data will encompass the data dictionary and de-identified data only. Any analysis will be conducted in collaboration with the LETHE Group. Access is subject to the LETHE legal framework. An access agreement will be prepared and signed by relevant parties.

Applications for data will be considered after the trial results have been published and data will be made available according to the terms of the access agreement.

As described above in the Plan Description.

Participants will not be actively told to what group they have been assigned (intervention or control). Outcome assessors will be blinded to the group allocation.