Associations of built environment features with multimorbidity: A systematic review protocol.

Introduction: Preventing or delaying multimorbidity (people living with two or more chronic conditions) is a public health priority. It is currently uncertain if multimorbidity is associated with features of the built environment, a term describing human-made or modified features of the surroundings in which humans live. Aims: To undertake a systematic review of the literature to determine if built environment features and interventions are associated with multimorbidity and to review the analytical methods used and their implications for causal inference. Methods: Four databases will be searched (Medline, Embase, Science Citation Index Expanded, and Social Sciences Citation Index) using a prespecified search strategy that incorporates terms for both multimorbidity and the built environment, which includes aspects of neighbourhood design, transport interventions, natural environment, food environments, and housing. Inclusion criteria will include: 1) involves community-based adult populations not selected based on an index condition; and 2) a built environment exposure or intervention was assessed; and 3) outcomes include multimorbidity prevalence, incidence, or trajectory. Reference lists of included studies and previous reviews will also be searched. Two reviewers will independently screen, data extract, and quality appraise (using the ROBINS-E or RoB 2 tool). Results will be synthesised by meta-analysis or, if heterogeneity is too great, according to Synthesis without meta-analysis (SWiM) guidelines. Results will be grouped by type of exposure or intervention and by study quality. Conclusions: This systematic review will improve understanding of built environment associations with multimorbidity. It could identify aetiological pathways that support the development of multimorbidity-preventative strategies.