Effectiveness of stress management interventions to change cortisol levels: a systematic review and meta-analysis.

Stress has a damaging impact on our mental and physical health, and as a result, there is an on-going demand for effective stress management interventions. However, there are no reviews or meta-analyses synthesising the evidence base of randomised controlled trials testing the effectiveness of psychological interventions on changing cortisol levels (the stress hormone) in non-patient groups. Therefore, the primary aim of this systematic review and meta-analysis was to address this gap. Six databases (Medline, PsychInfo, Embase, CINAHL, Cochrane and Web of Science) were searched (1171 studies identified) with 58 studies (combined N = 3508) included in the meta-analysis. The interventions were coded into one of four categories; mind body therapies, mindfulness, relaxation or talking therapies. A random effects meta-analysis on cortisol as measured in blood, saliva or hair found that stress management interventions outperformed pooled control conditions with a medium positive effect size (g = 0.282). The studies that utilised cortisol awakening measures (g = 0.644) revealed larger effects of stress management interventions than those that measured diurnal cortisol (g = 0.255). Mindfulness and meditation (g = 0. 345) and relaxation (g = 0. 347) interventions were most effective at changing cortisol levels, while mind body therapies (g = 0. 129) and talking therapies (g = 0.107) were shown to have smaller and non-significant effect sizes. Additionally, studies that utilised an active control group (g = 0. 477) over passive control group (g = 0.129) were found to have stronger effects. Length of the intervention, study quality, risk of bias, age and gender did not influence the effectiveness of interventions and there was no evidence of publication bias. Overall, the current findings confirm that stress management interventions can positively influence cortisol levels. Future research should investigate the longer term implications for health and health outcomes.