Interventions to prevent and treat multiple long-term conditions and their consequences across the life course: concepts and definitions.

Multiple long-term conditions (MLTC; also known as multimorbidity) constitute an important unmet health challenge. Designing and evaluating interventions to prevent and treat MLTC and their consequences is essential but difficult, due to heterogeneous risk factors, biological mechanisms, condition combinations, social and functional impacts of MLTC. To make progress, shared ways of describing and discussing interventions to prevent and treat MLTC and their consequences would bring consistency and clarity to this complex research area.In this position paper, we aim to provide a framework to address this recently articulated need. We propose a conceptual framework for placing MLTC interventions on a spectrum of prevention and treatment (from primordial to quaternary prevention). We consider different key intervention time points across the life course and how the focus of interventions may change from reducing risk factors in earlier life, through prevention of condition accumulation or progression in later life, to mitigating adverse consequences on symptoms and function as conditions progress. We propose taxonomies of interventions based on simple description but also on the existing World Health Organisation International Classification of Health Interventions taxonomy. We discuss principles of intervention development, focussing particularly on the need to target shared biological mechanisms and risk factors rather than attempting to treat or prevent each condition individually, and focussing on symptoms or consequences of MLTC that are prioritised by patients.Finally, we consider the attributes of effective MLTC interventions; we argue that ideal interventions should have robust evidence of efficacy and effectiveness, should be scalable and implementable within existing health and social care systems, should reduce (or at least not increase) health inequality, should be cost-effective, and should deliver major improvements over and above existing interventions, either at individual or population level. We recommend using this conceptual framework, taxonomy and criteria for assessing interventions together to organise the planning and evaluation of MLTC intervention research thereby accelerating progress in this important yet understudied field.