Exercise improves cardiorespiratory fitness in people with depression: A meta-analysis of randomized control trials

Highlights

• Compared to control conditions, exercise results in a moderate improvement in cardiorespiratory fitness (hedges g=0.6).

• The mean increase was 3.05 ml/kg/min, equating to reduction in mortality risk of 15% in the general population.

• Improvements in cardiorespiratory fitness were also observed in people with major depressive disorder.

• We propose a shift prioritising fitness over fatness in people with depression.

Abstract

Objective

Cardiorespiratory fitness (CRF) is an independent predictor of cardiovascular disease and all-cause mortality. CRF improves in response to exercise interventions, yet the effectiveness of such interventions to improve CRF among people with depression is unclear. We conducted a systematic review and meta-analysis to evaluate whether CRF improves in people with depression in exercise randomized control trials (RCTs).

Method

Three authors identified RCTs from a recent Cochrane review and conducted updated searches of major electronic databases. We included RCTs of exercise interventions in people with depression (including major depressive disorder (MDD) and above-threshold depressive symptoms) that reported CRF (defined as predicted maximal oxygen uptake (VO₂max predicted) or peak oxygen uptake (VO₂peak)) versus a control condition. A random effects meta-analysis was conducted.

Results

Seven unique RCTs including 8 aerobic exercise interventions for depression were eligible, including 293 people allocated to exercise (mean age=40.3 years, range=27.2–64.7years and 35–100% female) and 205 allocated to control conditions. Across all studies exercise results in a significant increase in CRF (g=0.64, 95%CI=0.32–0.96, p<0.001) equating to a mean increase of 3.05 ml/kg/min. Results remained significant when restricted to MDD only (N=5, g=0.41, 95%CI=0.18–0.64, p<0.001) and in high quality studies (N=5, g=0.60, 95%CI=0.19–1.00, p=0.004).

Conclusions

People with depression can achieve clinically relevant improvements in CRF in response to exercise interventions. Targeting ‘fitness’ rather than ‘fatness’ may be another feasible intervention strategy in this population.

Introduction

People with depression, including those with major depressive disorder (MDD) and sub-threshold depressive symptoms experience a marked increased premature mortality compared to the general population (Cuijpers et al., 2013, Cuijpers et al., 2014). The premature mortality observed in this population is primarily due to increased prevalence of metabolic (Vancampfort et al., 2015, Vancampfort et al., 2013) and cardiovascular diseases (Walker et al., 2015), with lifestyle factors such as low levels of physical activity playing an integral role.

In the general population, low cardiorespiratory fitness (CRF), defined as the ability of the circulatory and respiratory systems to supply oxygen to working muscles during sustained physical activity, is a strong and independent predictor of cardiovascular diseases (relative risk (RR) 1.56 (95% CI=1.39–1.75; P<0.001) and all-cause mortality (RR 1.70 (95% CI=1.51–1.92; P<0.001)) (Kodama et al., 2009). Improvements in CRF are associated with a reduced risk of mortality independent of age, smoking status and body composition (Lee et al., 2011). People experiencing depression have poorer CRF in comparison to the general population (Boettger et al., 2009, Nyboe et al., 2015, Voderholzer et al., 2011), while low fitness has been shown to be more strongly associated with elevated depressive symptoms compared to fatness (Becofsky et al., 2015). In recent years, the utility of exercise as medicine compared to control interventions (Cooney et al., 2013) or as an add-on therapy (Schuch et al., 2015) for people with depression has been repeatedly demonstrated. However the impact of exercise interventions on CRF among people with depression has been relatively underexplored.

To our knowledge, no meta-analytical data exists investigating the magnitude of CRF changes observed as a result of exercise interventions among people with depression. Only one previous broad narrative review (Krogh et al., 2014) has considered this question, with the authors suggesting that improvements in CRF are evident. Meta-analysis enables the pooling of data so that wider inferences can be made than when individual studies are considered separately (Ioannidis, 2009). Moreover, if exercise improves CRF in this vulnerable population, it would have important implications for tackling cardiovascular disease and mortality. Thus this brief report aims to conduct a systematic review and meta-analysis of CRF changes associated with exercise interventions in people with depression in comparison to control conditions.