Does massage therapy reduce cortisol? A comprehensive quantitative review.

Area of Science:

• Integrative Medicine
• Endocrinology
• Psychoneuroimmunology

Background:

• Massage therapy (MT) is widely believed to reduce cortisol levels, a mechanism proposed to explain its benefits for anxiety, depression, and pain.
• Existing reviews on MT's effect on cortisol are inconsistent regarding the existence, magnitude, and causative role of cortisol reduction.
• A definitive quantitative review is needed to clarify MT's impact on cortisol for research and clinical practice.

Purpose of the Study:

• To quantitatively review the effect of massage therapy on cortisol levels.
• To compare rigorous meta-analytic methods with an unconventional approach used in previous reviews.
• To determine if cortisol reduction is a plausible mechanism for the clinical benefits of MT.

Main Methods:

• A comprehensive literature search and retrieval was conducted.
• Rigorous meta-analytic methods were used to calculate between-groups effect sizes.
• An unconventional method quantifying within-group percentage change in cortisol was replicated for comparison.

Main Results:

• Between-groups effect sizes for MT's effect on cortisol were generally small (ds = 0.05–0.30) and not statistically significant.
• The only significant effect was observed in children receiving multiple MT doses (d = 0.52), but this was based on limited studies and vulnerable to bias.
• Within-group percentage reductions in cortisol were smaller and inconsistent with between-groups results, highlighting methodological limitations.

Conclusions:

• Massage therapy's effect on cortisol levels is generally very small and often not statistically significant.
• Cortisol reduction is unlikely to be the primary mechanism behind MT's established benefits for anxiety, depression, and pain.
• Other unidentified mechanisms are likely responsible for the clinical efficacy of massage therapy.