Dose–response relationship between physical activity and mortality in people with non-communicable diseases: a study protocol for the systematic review and meta-analysis of cohort studies

INTRODUCTION: This study protocol outlines our planned systematic review and dose-response meta-analysis of postdiagnosis physical activity and mortality in people with non-communicable diseases (NCDs). METHODS AND ANALYSIS: This study is based on the Preferred Reporting Items for Systematic Reviews and Meta-analysis for Protocols. A systematic literature search will be conducted in various databases—namely, PubMed, Scopus and Web of Science—by two researchers in order to identify prospective observational studies that investigate postdiagnosis physical activity or activity-related energy expenditure and mortality in individuals with NCDs. The target population is adults (≥18 years of age) with one of the following nine NCDs: low back pain, type 2 diabetes mellitus, osteoarthritis, depressive disorder, chronic obstructive pulmonary disease, breast cancer, lung cancer, stroke or ischaemic heart disease. We will focus on all-cause mortality as the primary outcome and investigate indication-specific mortality as the secondary outcome. For each study identified as a result of the literature search, we will conduct graphical dose-response analyses of mortality as a function of activity-related energy consumption. If more than two studies are available for one disease, we will perform linear and non-linear dose-response meta-analyses for said disease using random-effects models. We will investigate the heterogeneity of the studies and publication bias. To assess the risk of bias and the quality of the included studies, we will use the Risk Of Bias In Non-randomised Studies - of Interventions tool, which is a Cochrane tool. ETHICS AND DISSEMINATION: This systematic review will be conducted in compliance with ethical precepts. As the systematic review is based on published studies, approval from an ethics committee is not required. The systematic review and meta-analysis will be published in a peer-reviewed journal. PROSPERO REGISTRATION NUMBER: CRD42018103357