Are lower levels of cardiorespiratory fitness associated with incident depression? A systematic review of prospective cohort studies.

Physical activity (PA) is protective from future depression, however, the potential impact of cardiorespiratory fitness (CRF) on the development of depression is less clear. We aimed to investigate if lower levels of CRF are associated with a higher risk for depression onset. Major electronic databases were searched, from inception to January 2016 for prospective cohort studies evaluating the association between CRF and incident depression. Pooled hazard ratio (HR) with 95% confidence intervals (CIs) were calculated. Methodological quality was evaluated using the Newcastle-Ottawa scale (NOS). Three prospective studies were identified and data from two studies were pooled. Our data provide preliminary evidence found that people with low CRF and medium CRF were at increased risk of developing depression (n=1,128,290, HR=1.76, 95% CI 1.61-1.91, p<0.001, I2=11.88, and HR=1.23, 95% CI 1.20-1.38, p<0.001, I2=0, respectively). Considered alongside the wider benefits of higher levels of CRF, these findings further support the rationale for interventions specifically targeting fitness, in order to reduce the significant burden associated with depression.