Prospective cohort study for digital health research in Germany (DigiHero): objectives, design and baseline characteristics.

DigiHero is a population based, nationwide digital cohort study with participants from more than 120 000 households from all federal states in Germany. It was set up during the COVID-19 pandemic to contribute to the rapid collection of COVID-19 related data but already at its set-up, it was intended to be a research platform to study (chronic) diseases, health behaviour, and healthy ageing. Later on, it became part of the German Center for Mental Health and contributes to its research agenda. Participants were recruited via postal invitations with address information obtained from administrative registries; the participation is fully online, with four regular contacts per year. A wide array of exposures is being assessed, with particular focus on change over time. In addition to regularly repeated modules, the flexibility of the study design allows to implement further questionnaires responding to newly emerging health topics. Self-collected bio samples or examinations in study centers or even in medical practices can be included in subprojects. Data from wearables, sensors, and linked health insurance data will enrich the responses to questionnaires. With focus on new digital approaches, DigiHero can react directly and quickly to current health issues, generating health-related data promptly and cost-effectively. Given its fully virtual participation, DigiHero supplements local or study-center associated cohorts in Germany. It is intended to reflect regional heterogeneity with inclusion of rural regions across Germany.