Aims: The aim of this study was to investigate the usefulness of cortisol as a marker of improvement in mindfulness intervention research. Cortisol is a bio-marker of stress that can provide a useful physiological indicator of well-being. It is increasingly included in examinations of mindfulness efficacy but its use has yet to be systematically evaluated. Incorporating psychophysiological markers of well-being in intervention research has the potential to allow more robust evaluations of the effect of health and well-being interventions.
Methods: A systematic review of research examining the effect of mindfulness interventions on cortisol was conducted. Seventy-one potential studies were retrieved; of these, 12 studies were eligible for inclusion in the study. Studies were evaluated based on cortisol outcomes, including the cortisol awakening response and diurnal slope. The methodological approach to evaluating changes in cortisol levels over time in each study was also evaluated.
Results: Significant changes in cortisol levels were observed in within-subjects studies in diverse groups. Mindfulness did not demonstrate changes in cortisol levels when compared with control groups however. Methodological issues may have influenced these results. Such issues involve timing and frequency of cortisol collection, the use of control groups and participant adherence and attrition.
Conclusions: Mindfulness interventions demonstrate the potential to improve cortisol functioning over time. Inconsistent findings within the literature may be due to methodological differences between studies. It is essential to develop and implement thorough cortisol collection protocols in order to rigorously examine the effects of mindfulness interventions.