Abstract
Background: Depression currently affects 4.4% of the global population, and 93.7% of this population suffer from major depressive disorder (MDD) according to 2017 statistics. MDD patients are more likely to suffer from co-morbidities such as cardiovascular disease and high body mass index (BMI), thus contributing to its large cost to society. Throughout the literature, there are known links between inflammation and MDD. Interestingly, while exercise is considered a promising intervention for MDD, the mechanism(s) of action remain unclear, thereby preventing the creation of optimal, cost-saving, exercise "prescriptions" for those with MDD. Thus, the aim of this review and meta-analysis is to summarize and analyse the current literature exploring how quantified exercise interventions modulate inflammatory molecules in MDD patients. Methods: Electronic databases (APA PsycINFO, and PubMed/MEDLINE (EBSCO interface), EMBASE) will be searched using a detailed search strategy comprised of three search term themes: exercise, depression/MDD, and inflammation/inflammatory molecules. Only quantified exercise interventions performed in adult humans with MDD validated via a recognized diagnostic criterion will be included. Studies should also include a MDD control group and explore changes in inflammatory molecules. Examples of these molecules include: C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-1 beta (IL-1b), tumour necrosis factor-alpha (TNF-a), homocysteine, d-dimer and myeloperoxidase (MPO). After eligible studies are identified, standardized data extraction will be employed and the risk of bias in each study will be appraised using the Cochrane handbook checklists. In the event of two or more homogenous studies exploring exercise effects over a similar period of time, raw mean differences or standardized mean differences will be pooled using random effects analysis. This systematic review and meta-analysis will be reported according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Dissemination: This systematic review and meta-analysis will be disseminated in peer-reviewed journals. PROSPERO registration: CRD42020186006 (31/08/2020).
Highlights
Rationale Depression is a leading cause of disability worldwide, affecting more than 300 million people or 4.4% of the global population today[1]
By providing an up-to-date systematic review and metaanalysis, this study will synthesize current evidence of how exercise interventions modulate inflammatory molecule levels in those with diagnosed major depressive disorder (MDD) compared to controls
Changes in pre- and post-intervention inflammatory molecule levels will be statistically summarised via meta-analysis, which will analyse acute and chronic exercise interventions, separately
Summary
Rationale Depression is a leading cause of disability worldwide, affecting more than 300 million people or 4.4% of the global population today[1]. According to the Global Burden of Disease (GBD), the number of incident cases of depression worldwide has seen a steep increase from 172 million in 1990 to more than 258 million in 2017, whereby a large majority (93.7%) of these patients with depression suffer from major depressive disorder (MDD)[2]. The connection between inflammation and MDD is wellrecognized throughout the literature[5,6,7,8,9] The mechanism of this relationship is described by the inflammation/cytokine model of depression, which purports that a pro-inflammatory state caused by an increase in pro-inflammatory cytokines and/or the reduction in anti-inflammatory cytokines results in the development of clinical depression in humans[10,11,12]. The aim of this review and meta-analysis is to summarize and analyse the current literature exploring how quantified exercise interventions modulate inflammatory molecules in MDD patients. Studies should include a MDD control group and explore changes in inflammatory molecules.
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