Consistent with our hypotheses, mindfulness meditation led to a significantly greater increase in state mindfulness compared to the control conditions. Further, additional analyses revealed that this effect was moderated by trait mindfulness, such that meditation (relative to control) increased state mindfulness especially among participants with lower trait mindfulness. This finding suggests that individuals with relatively low trait mindfulness have more “room for improvement” with regards to state mindfulness, perhaps akin to how people beginning an exercise program for the first time can experience relatively fast changes in physical fitness with even modest effort.
Notably, contrary to our hypotheses, we found no significant differences between meditation and control conditions on anxiety or negative affect. We were also surprised to find no differences between the 10- and 20-minute meditation conditions, suggesting that a higher “dose” of meditation was not associated with overall greater changes in any of the outcomes measured in this study. However, moderation analyses found that meditating for 20 vs. 10 minutes led to greater decreases in state anxiety for participants with higher trait mindfulness. Taken together, these findings suggest that 10-minutes of mindfulness meditation may be just as effective as 20-minutes in improving state mindfulness for the majority of people, which runs counter to the popular notion that “more is always better.” Indeed, given the often-used metaphor of mindfulness being a muscle that’s strengthened with practice, these findings may come as a surprise. Nevertheless, it is possible that typical-dose response relationships may exist at higher doses than measured in this study, and/or that 10 and 20 minutes of meditation are close to each other on the dose-response curve (at least for this sample). It is also possible that the dose-response relationship for MBIs follow a U-shaped curve28. Thus, future research could test additional durations to better understand the nature of dose-response relationships in single sessions of meditation.
Another interpretation is suggested by the finding of Strohmaier et al15, who previously found that four 5-minute meditation sessions over two weeks – as compared to four 20-minute sessions over two weeks – resulted in greater increases in state and trait mindfulness and greater decreases in stress, with similar trends for depression and anxiety. Taken together with the current findings, Strohmaier’s findings may suggest that some dose-response relationships with MBIs require multiple meditation sessions to manifest to a statistically significant degree. This hypothesis is in line with the popular notion that MBIs cultivate new habits and qualities of mind that must be practiced repeatedly in order to be deeply learned and embodied, much like learning to play an instrument. As such, it may be that single-session MBIs induce a limited degree of consolidation of these new skills and that these changes are strengthened with repeated practice over multiple sessions.
Another important consideration is that the lack of differences between meditation and control may have been due in part to a floor effect, since 55% and 56.5% of participants reported the lowest possible level of state anxiety and negative affect, respectively, pre-intervention. Indeed, many studies of single-session mindfulness meditations have induced anxiety or rumination in participants before or after instructing them to practice mindfulness, thereby increasing the “room for improvement”29–31. Relatedly, it’s conceivable that dose-response relationships may have appeared had these sorts of provocations been incorporated.
The findings of the current study also suggest that the optimal duration of a single meditation session may vary according to an individual’s level of trait mindfulness. Moderation analyses indicated that meditating for 20 minutes (vs. 10 minutes) predicted greater decreases in state anxiety among individuals with relatively higher trait mindfulness. There could be several possible interpretations for this finding, including the possibility that individuals higher in trait mindfulness may benefit more from longer periods of practice relative to those low in trait mindfulness. However, it is notable that prior research that used a different measure for trait mindfulness found that high levels of certain facets of mindfulness and low levels of other facets were associated with better improvements in state anxiety in a single-session MBI26. However, given the use of different measures of trait mindfulness, it is difficult to compare these findings and draw conclusions. Thus, further research with multiple mindfulness measures and larger samples is warranted to disambiguate these effects.
Contrary to our expectations, prior meditation experience did not moderate the effects of the interventions. This finding may be at odds with the results of a prior study that found that participants with prior meditation experience had higher levels of state mindfulness following an eight-minute, single-session MBI as compared to meditation-naïve participants26. One possible explanation for these differing findings is that the participants with prior meditation experience in the aforementioned study could have had a different amount of prior meditation experience than did participants in the current study. This possibility highlights the importance of developing a standardized way for assessing participants’ prior meditation experience, thereby enabling more precise and effective comparisons within and between studies. Nevertheless, our finding suggests that meditation-naïve participants can follow mindfulness instructions and experience meaningful improvements from a single meditation to a degree comparable to people with prior experience. Additionally, it seems that both 10 and 20 of minutes of meditation are reasonable durations of meditation for meditation-naïve individuals.
It is also noteworthy that neuroticism did not moderate the interventions’ effects. Prior research using the same ten-minute meditation and control scripts found that neuroticism moderated the interventions’ effects on measures of attention25, such that participants with lower neuroticism tended to perform better on various measures of attention following a ten-minute meditation than did participants with higher neuroticism. Additionally, other research has found that neuroticism moderated the effects of a four-session meditation training, such that participants with higher neuroticism experienced greater reductions in negative mood, perceived stress, state anxiety, and psychological distress32. It may be the case that neuroticism moderates the effects of single-session interventions only for certain outcomes (e.g., attention), whereas neuroticism’s moderation of multi-session interventions’ effects may include additional outcomes as well (e.g., mood and anxiety). Consequently, further research on the moderating effects of neuroticism on single- and multi-session mindfulness interventions is warranted.
Since the only significant difference between the meditation and control conditions in the current study was a greater increase in state mindfulness in the meditation conditions, it is possible that acute changes in state mindfulness, and not acute changes in affect, could be a proximal mechanism of action by which MBIs exert their beneficial effects on mental wellbeing, as other have previously suggested33–35. Indeed, while one study on MBIs did not support the mediating role of state mindfulness15, other studies have found that state mindfulness mediates a variety of positive outcomes of both single- and multi-session MBIs, including positive emotions, hope, gratitude, trait mindfulness, and psychological distress36–38.
Given the mainstream perception of mindfulness as a stress-relieving panacea, the large degree to which the effects of the control conditions resemble those of the meditation conditions in this study may be surprising. The control conditions’ anxiolytic and mindfulness-boosting effects may have been due to a combination of factors, including the speaker’s soothing voice, the potentially anxiolytic content of the audio recording (i.e., the history of sequoia trees), and the intermittent periods of silence. Further, these findings are fairly consistent with prior research comparing mindfulness meditation to sham meditation39,40, which supports the importance of using strong controls in mindfulness research and of identifying both specific and unique effects and mechanisms of action.
This study has multiple strengths, one of which is the diversity of the participants with respect to age, gender, and ethnicity. Many studies of MBIs have relied upon local university students or adults, which can limit the generalizability of the findings. Relatedly, the study’s sample size is larger than that of many single-session MBIs in the published literature, which further increases the generalizability of the current findings and increases the study’s power.
Another strength of this study is the use of active control conditions, specifically one that has been used in prior published research. A common criticism of mindfulness research has been the frequent use of passive control conditions, which has likely led to an inflated estimate of the effectiveness of MBIs41–44. Additionally, so as to help isolate the unique effects of the mindfulness components of the intervention, the control conditions in the current study were designed to match the mindfulness recordings in terms of word count, pace of speech, tone of voice, and periods of silence.
This study has several limitations. Perhaps most importantly, this study only sheds light on the effects of the duration of a single session of mindfulness meditation and may not generalize to multi-session MBIs. Further, as the outcomes were measured immediately before and after the intervention, further research would be needed to assess the longevity of any intervention’s effects. For example, although 10- and 20-minute meditations may lead to comparable increases in state mindfulness immediately after the meditation, it may be that the increases persist longer in participants who completed the 20-minute meditation (or vice versa).
Another limitation is that the setting in which participants completed the study was not standardized or directly supervised, as would be the case if the study were conducted in person. Indeed, although we used multiple methods to ensure participants’ attentiveness and comprehension (and excluded participants who endorsed or demonstrated poor adherence to or understanding of instructions), it is still possible that some participants who were included in the final analysis were minimally attentive. Thus, a possible explanation for the lack of a dose-response relationship is that the overall quality of meditation practice (i.e., the total time spent “actively meditating”) may not have differed between meditation conditions due to high rates of mind-wandering that may have occurred during the prolonged periods of silence in the 20-minute condition. This phenomenon would be unsurprising, given that a high frequency of mind-wandering has been found in the general population45,46. Consequently, future studies could attempt to measure the frequency or duration of participants’ mind-wandering and on-task mindful awareness as well as meditation practice quality47,48.
Consistent with our hypotheses, mindfulness meditation led to a greater increase in state mindfulness compared to control conditions, an effect which was moderated by trait mindfulness. Moderation outcomes also revealed that trait mindfulness moderated the effect of meditation duration on changes in state anxiety. To our surprise, however, we found no other differences between the two durations of meditation, which raises important questions about the nature of dose-response relationships in MBIs. Additionally, neuroticism and prior meditation experience were not found to moderate effects of the interventions. Future research will hopefully further investigate dose-response relationships and moderators of single- and multi-session MBIs.