Depression Symptom Severity and Cardiorespiratory Fitness in Healthy and Depressed Adults: A Systematic Review and Meta-Analysis

Background: Depression symptom severity and cardiorespiratory fitness (CRF) are significant predictors of mortality and disability. However, the relationship between the two is unclear. Objective: This meta-analysis assessed the relationship between depression symptom severity and CRF in healthy and depressed adults (aged 18 years and over). Search Methods: The PubMed, Cochrane Library, Google Scholar and ProQuest databases were browsed for relevant English-language studies published from January 2000 to August 2014. Selection Criteria: Studies reporting a correlation between a depression scale and maximum oxygen consumption (VO_2peak), as well as studies from the data of which such a correlation could be calculated, were included in this analysis. Data Analysis: Correlation coefficients (CCs) were converted to Fisher’s z values, and the analysis was performed using a random-effects model. Then, summary effects and 95 % confidence intervals (CIs) were converted back to CCs. Results: Sixteen studies (totalling 4039 participants) were included in this analysis. A modest correlation between depression symptom severity and CRF was found (CC −0.16, 95 % CI −0.21 to −0.10), appearing stronger in male participants (CC − 0.22, 95 % CI −0.26 to −0.18) than in female participants (CC −0.12, 95 % CI −0.19 to −0.05; p = 0.01). There was no difference in the summary effect between healthy and depressed adults (p = 0.43). Heterogeneity was moderate (I² = 33 %; p = 0.09). Conclusions: Depression symptom severity is inversely correlated with CRF, and this correlation is stronger in men than in women. Clinical and prognostic implications of the correlation are discussed. These findings should stimulate further research on the effects of treating one variable on the other.