Our body’s adaptive response to a stressor occurs in temporal phases and is the outcome of complex interactions between the sympathetic and parasympathetic nervous systems and the endocrine system. This phased time scale is the outcome of feedback loops between the systems and the time it takes for stress hormones to both enter the blood stream and subsequently be deactivated. Many studies ignore this complexity by measuring stress at a single timepoint or with only a sole biomarker. 

Gamaiunova, et al. [Biological Psychology] tested the effects of two different mindfulness-based interventions on multiple biological measures of stress across different temporal phases of the stress response. A better understanding of the temporal dynamics of these measures might help us better understand discrepancies between studies that show different results.

The researchers randomly assigned 99 healthy Swiss adult volunteers to Mindfulness-Based Stress Reduction (MBSR), Buddhist-enhanced Mindfulness-Based Stress Reduction (MBSR-B), or a waitlist control. Attrition was high, and data from only 65 participants (average age = 29 years; 65% female) were analyzed. MBSR was taught in 8 weekly 2.5-hour sessions with a 7th week retreat day and 55 minutes a day of homework. MBSR-B was similarly structured but included additional material on the Buddhist themes of impermanence, ethics, lovingkindness, compassion, non-self, and craving.

Following the study interventions, participants completed a social stress task in a laboratory setting. After being hooked up to an electrocardiograph (EKG), participants rested for ten minutes. Participants were then given 15 minutes to prepare a talk as part of a stress task. During the stress task, participants gave 5-minute speeches and engaged in 5 minutes of mental arithmetic while being recorded on camera and observed by two research assistants wearing white lab coats. The participants then remained in the lab for a 30-minute recovery period. EKGs were recorded from the start of the rest period through the recovery period. 

Saliva samples of cortisol (a stress hormone) and α-amylase (a surrogate for serum epinephrine and norepinephrine) were drawn during the rest, anticipation, task, and recovery periods. EKGs were analyzed for heart rate variability and the duration of the pre-ejection period. Heart rate variability increases due to parasympathetic activity, and the pre-ejection period shortens due to sympathetic activity. Participants were also asked to rate their positive and negative affect during rest, anticipation, task, and recovery.

The results showed both MBSR groups had significantly lower cortisol levels under the curve during the anticipatory period than controls (d=0.78-0.82). They also showed significantly lower relative percent decreases in pre-ejection period duration than controls during the anticipatory (d=0.71-0.82) and task (d=0.70-0.87) periods, but not during the recovery period. Both MBSR groups showed a significantly lesser relative percent decrease in heart rate variability during the anticipatory (d = 0.72-0.88) and task (d = 0.88-1.05) periods than controls, but only the MBSR-B group showed a significant effect (d = 1.10) during the recovery period when compared to the control group. 

The MBSR-B group reported smaller increases in negative affect than controls during the anticipatory phase (d=.97) while both treatment groups reported smaller increases in negative affect during the task phase (d=0.95-0.88). The treatment groups also reported smaller declines in positive affect than controls during the task phase (d =0.95-0.91). No between-group differences were noted for α-amylase levels.

The study shows MBSR and MBSR-B both reduce subjective and biological components of the laboratory-induced stress response, but these effects vary depending on the measure used and the phase of the stress response during which they were measured. The study was limited in its power to detect significant differences due to its relatively high attrition rate.

Reference:

Gamaiunova, L., Kreibig, S. D., Dan-Glauser, E., Pellerin, N., Brandt, P.-Y., & Kliegel, M. (2022). Effects of Two Mindfulness Based Interventions on the Distinct Phases of the Stress Response Across Different Physiological Systems. Biological Psychology.

Link to study