The Association of Lifestyle and Mood with Long-Term Levels of Cortisol: A Systematic Review

Objectives: To critically review evidence for associations between long-term cortisol levels, mood, and lifestyle factors.Systematic searches of electronic databases (MEDLINE, EMBASE, PsycINFO, WoS, and CINAHL) were conducted up to 21/11/2020 to identify observational and interventional studies (n = 4971) reporting associations between one or more lifestyle or mood factor with cortisol outcomes measured over >= 4 weeks in healthy adults. Quality of included studies was assessed using Downs and Black checklist. The quality of evidence supporting the associations of lifestyle and mood with long-term cortisol levels was assessed as being of moderate-to-poor quality. Observational studies (n = 25) indicated positive associations for BMI/body weight (ESr, pooled effect size correlation = 0.15, p<.001), physical activity (ESr=0.16, p<.001), perceived stress (ESr=0.114, p = .02), and depression (ESr = 0.133, p = .02), but not stressors (ESr = 0.06, p = .29), anxiety (ESr = 0.08, p = .14), or specific features of stress (ESr = 0.25, p = .10). There was insufficient evidence to reliably estimate associations between long-term cortisol levels and sleep, smoking, alcohol consumption, caffeine consumption, and PTSD. Findings from interventional studies (n = 27) were mixed and did not always support the relationships found in observational studies. The findings of this review were limited by the quality of the evidence. Current evidence for associations between mood and lifestyle factors with long-term levels of cortisol is mixed. For many factors, there was considerable uncertainty regarding the size of association with long-term cortisol due to a paucity of evidence. Future research should aim to (1) follow more consistent sampling protocols between studies and (2) clearly describe the hypothesised mechanisms through which interventions would affect cortisol levels.