Effectiveness of diaphragmatic breathing for reducing physiological and psychological stress in adults: a quantitative systematic review
Authors: Hopper Susan I. , Murray Sherrie L. , Ferrara Lucille R. , Singleton Joanne K. 
Published: August 2019

ABSTRACT

Objective:
The objective of this review was to evaluate the effectiveness of diaphragmatic breathing for reducing physiological and psychological stress in adults 18 years and over.

Introduction:
Stress has reached epidemic proportions globally. Unidentified sequela of physiological and psychological stress can result in anxiety, depression, heart disease, cancer, immunologic conditions and death. There is a high cost associated with the treatment of stress related health conditions in the United States and worldwide. Many treatments are pharmacologic and cannot be self-initiated. Therefore, it is critical to identify evidence-based, low-cost, non-pharmacologic, self-administered interventions that can mitigate physiological and psychological stress.

Inclusion criteria:
This review considered adults 18 years and over engaged in diaphragmatic breathing as an isolated intervention to reduce physiological and psychological stress. There were no exclusions based on physical or psychological conditions. The comparator was no treatment or usual treatment, which may constitute ordinary breathing.

Methods:
The comprehensive literature search included published and unpublished studies in English from the beginning of the databases through January 2018. The databases searched included: PubMed, CINAHL, Cochrane Central Register of Controlled Trials (CENTRAL), Embase, PsycINFO, ProQuest Nursing and Allied Health and Health Source: Nursing/Academic Edition. The recommended JBI approach to critical appraisal, study selection, data extraction and data synthesis was used.

Results:
Three studies met the criteria for review: one randomized controlled trial and two quasi-experimental studies. Statistical pooling was not possible due to clinical and methodological heterogeneity of interventions and outcome measures of the included studies. All three studies demonstrated the effectiveness of diaphragmatic breathing on reducing stress. One study showed improvement in the biomarkers of respiratory rate and salivary cortisol levels, one showed improvement in systolic and diastolic blood pressure, and one study showed an improvement in the stress subscale of the Depression Anxiety Stress Scales-21 (DASS-21) after implementation of a diaphragmatic breathing intervention. Although there were limitations across the studies, such as sample size, and length and duration of the intervention over time, ranging from one 20-minute intervention to nine months, the studies demonstrated that diaphragmatic breathing had a positive effect on lowering physiological and psychological stress.

Conclusions:
The evidence suggests that diaphragmatic breathing may decrease stress as measured by physiologic biomarkers, as well psychological self-report tools. Given the benefits of diaphragmatic breathing on stress reduction, ongoing research is needed to continue to establish the evidence-base for this self-administered, low-cost, non-pharmacologic intervention.