Elsevier

Psychoneuroendocrinology

Volume 68, June 2016, Pages 117-125
Psychoneuroendocrinology

Reduced stress and inflammatory responsiveness in experienced meditators compared to a matched healthy control group

https://doi.org/10.1016/j.psyneuen.2016.02.013Get rights and content

Highlights

  • Meditators had smaller cortisol and flare responses relative to non-meditators.

  • Meditators perceived the TSST as less stressful than non-meditators.

  • Cortisol response was positively associated with size of the flare response.

  • Meditators showed closer alignment between measured and perceived stress responses.

Abstract

Psychological stress is a major contributor to symptom exacerbation across many chronic inflammatory conditions and can acutely provoke increases in inflammation in healthy individuals. With the rise in rates of inflammation-related medical conditions, evidence for behavioral approaches that reduce stress reactivity is of value. Here, we compare 31 experienced meditators, with an average of approximately 9000 lifetime hours of meditation practice (M age = 51 years) to an age- and sex-matched control group (n = 37; M age = 48 years) on measures of stress- and inflammatory responsivity, and measures of psychological health. The Trier Social Stress Test (TSST) was used to induce psychological stress and a neurogenic inflammatory response was produced using topical application of capsaicin cream to forearm skin. Size of the capsaicin-induced flare response and increase in salivary cortisol and alpha amylase were used to quantify the magnitude of inflammatory and stress responses, respectively. Results show that experienced meditators have lower TSST-evoked cortisol (62.62 ± 2.52 vs. 70.38 ± 2.33; p < .05) and perceived stress (4.18 ± .41 vs. 5.56 ± .30; p < .01), as well as a smaller neurogenic inflammatory response (81.55 ± 4.6 vs. 96.76 ± 4.26; p < .05), compared to the control group. Moreover, experienced meditators reported higher levels of psychological factors associated with wellbeing and resilience. These results suggest that the long-term practice of meditation may reduce stress reactivity and could be of therapeutic benefit in chronic inflammatory conditions characterized by neurogenic inflammation.

Introduction

Psychological stress is now widely accepted as an important trigger of inflammation and a major contributor to symptoms of chronic inflammatory disease (Pace et al., 2009, Rohleder, 2014, Steptoe et al., 2001, Weik et al., 2008). As such, the impact of behavioral interventions designed to reduce psychological stress, such as meditation training, on inflammatory outcomes has been a growing focus of interest and attention by the scientific community. The overwhelming majority of studies addressing this question have randomly assigned participants to relatively short interventions (Bower and Irwin, 2015, Gu et al., 2015, Khoury et al., 2015). While this design is considered the gold-standard and has considerable merit, it also has some shortcomings when applied to behavioral interventions, that may be reflected in the mixed results reported in the literature (Black et al., 2015, Malarkey et al., 2013, Morgan et al., 2014, Rosenkranz et al., 2013). First, the ability of these interventions to reliably reduce stress may be highly variable across individuals and/or of small effect size in the early stages of training, perhaps becoming more stable and more easily detectible when the trained skills become more established. Second, the efficacy of any behavioral intervention is predicated upon an individual’s engagement with the training and the persistence of practice, unlike in a pharmaceutical trial, where one can be fairly confident that every individual is receiving roughly the same dose. Outside of the laboratory, individuals choose pathways of change that they are most drawn to, or for which they have some aptitude. Choice is a strong predictor of adherence to and engagement in an intervention (Lindhiem et al., 2014, Rennie et al., 2007) and effect sizes have been shown to be higher when an intervention is individually initiated, rather than part of a volunteer effort (Brown et al., 2015). Thus, through random assignment, these studies may unintentionally reduce the effect size of the intervention. As a complement to the extant RCTs, the current study was designed to compare individuals with a long-standing and self-initiated practice of meditation to a carefully matched group of healthy, non-meditating community volunteers in stress- and inflammatory responsiveness.

Major advances have been made in the last decade in our understanding of the mechanisms that underlie the relationship between stress and inflammation. However, most of these advances have been focused on the impact of stress on brain-immune pathways that function systemically, whereas very little attention has been paid to pathways through which stress modulates inflammation locally. Though systemic elevations in inflammatory markers are not uncommon in individuals suffering from chronic inflammatory diseases, local inflammatory processes are often more sensitive indicators of disease onset and progression (Bamias et al., 2013, Lotti et al., 2014, Riol-Blanco et al., 2014, Schleich et al., 2014, Ugraş et al., 2011) and the two are not always highly correlated (Davel et al., 2012, Lima et al., 2015, Malinovschi et al., 2013, Schleich et al., 2014, Vernooy et al., 2002). For this reason, we chose capsaicin application to skin as our model to investigate stress responsiveness and local neurogenic inflammation in long-term meditators and community controls.

Capsaicin is a naturally occurring compound found in hot peppers that imparts their “hotness”. It causes depolarization of predominantly C-fiber type sensory neurons by binding to vanilloid receptors (sub-type 1; TRPV1), leading to a descending impulse or axon reflex. The axon reflex travels down branches of the same sensory nerve, causing neuropeptide release from nearby terminals. When these neuropeptides are released in the skin, they evoke a neurogenic inflammatory response, characterized by a “flare response” − the area of redness or erythema that extends beyond the area covered by capsaicin, which is caused by nerve-mediated vasodilation (Helme and McKernan, 1985, Holzer, 1988).

We hypothesized that long-term meditators (LTMs) would have a smaller physiological stress response to an acute laboratory stressor and a reduced flare response to capsaicin application. Further, we predicted that the reduction in stress response would account for a significant amount of variance in the size of the flare. Finally, we hypothesized that smaller stress hormone and flare responses would be associated with lower perceived stress and better mental and physical well-being.

Section snippets

Participants

Our participants included 37 meditation-naïve participants (MNP; average age 48.0 ± 10.4 years, 25 female) and 31 long-term meditators (LTM; average age 50.7 ± 10.1 years, 17 female). The groups did not differ in socioeconomic status (SES) as measured by the Hollingshead Index of Social Position (t(66) = −.56, p = .58) or by family income (t(66) =.47, p = .64). Descriptive statistics can be found in Table 1. MNPs were recruited within Madison, WI and the surrounding community using flyers, online

Results

The outcome of analyses testing for group differences in biological variables showed a significant effect of group on both cortisol AUC (F(1, 59) = 5.03, p = .029), after controlling for the effects of age and sex, and flare peak1

Discussion

Our results suggest that individuals with a long-term meditation practice experienced less stress in response to the TSST, as indicated by both self-report and salivary cortisol measures, compared to a control group with no meditation experience. Moreover, though the difference between the correlations was not statistically significant, the perception of stress in response to the TSST more closely reflected the HPA-axis response in long-term meditators, suggesting that this group may have

Conflict of interest

Dr. Richard J. Davidson serves on the board of directors for the following non-profit organizations: The Mind and Life Institute and the Center for Investigating Healthy Minds, Inc.

Contributors

MAR conceived of and designed the study, analyzed the data, and wrote the manuscript.

AL contributed to the conception and design of the study, interpretation of data, and revision of the manuscript.

DMP contributed to analysis of the data and revision of the manuscript.

DRWB contributed to data acquisition and revision of the manuscript.

BSS contributed to analysis of the data and preparation and revision of the manuscript.

DGM contributed to conception and design of the study.

RJD contributed to

Acknowledgements

This research was supported by the National Center for Complementary and Integrative Health (NCCIH) P01AT004952 to RJD & AL, a core grant to the Waisman Center from the National Institute of Child Health and Human Development (NICHD) P30HD003352 to Albee Messing, and generous donations from individuals to the Center for Investigating Healthy Minds. No donors, either anonymous or identified, have participated in the design, conduct, or reporting of research results in this manuscript.

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