Daily stress events assessed in daily life each evening for one week at two time points via end-of day diary, totaling up to 7 assessments at each time point. All 7 assessments at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in logistic MLM analyses. Outcomes will be reported as mean percentage of days at each time point that stress events were endorsed, with higher percentages indicating more stress events.

Heart Rate (HR) measured continuously in daily life, with HR averaged in 30-minute windows around daily life stress reported via EMA up to four times per day for one week at two time points, totaling up to 28 windows at each time point. All (up to) 28 assessments at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher scores indicate higher HR in beats per minute (relative to an individual's average daily HR) at high stress moments (relative to an individual's average perceived stress).

Retention benchmark: >80% retention through intervention and >75% retention through post-intervention assessments

Adherence benchmark: average completion of at least 7 of 11 MBSR sessions

Adherence benchmark: average completion of >75% of ambulatory assessments

Adherence benchmark: collecting Fitbit sensor data on >75% of days

Safety benchmark: <10% of participants showing substantial (>2SD) increases in anxiety, trauma, or depressive symptoms (using PROMIS Anxiety and Depression scales and Posttraumatic Stress Disorder Checklist-Civilian scale described in other outcomes below) combined to create treatment-emergent symptom rate

Acceptability of interventions, with benchmark of >80% of participants giving positive ratings of treatment expectancies (>3 on 6-item Credibility/Expectancy Questionnaire)

Childhood SES indexed via parental educational attainment, ranging from less than high school education to doctoral degree (1 = No High School Diploma, 2 = GED, 3 = High School Diploma, 4 = Technical Training, 5 = Some College, no degree, 6 = Associate Degree, 7 = Bachelor's Degree, 8 = Master's Degree, 9 = MD, PhD, JD, or PharmD), with higher scores indicating higher educational attainment

Childhood SES assessed via National Comorbidity Survey: Adolescents item assessing government food assistance

Early Life Adversity assessed via Adverse Childhood Experiences Survey (using a 5-item domestic violence subscale, ranging from 0-10, with higher scores indicating higher levels of domestic violence)

Circulating IL-6 assessed via dried blood spot (DBS) [additional funding needed to assess]

Circulating IL-10 assessed via dried blood spot (DBS) [additional funding needed to assess]

Circulating TNF assessed via dried blood spot (DBS) [additional funding needed to assess]

Circulating uPAR assessed via dried blood spot (DBS) [additional funding needed to assess]

Circulating CRP assessed via dried blood spot (DBS) [additional funding needed to assess]

State positive affect assessed in daily life four times per day for one week at two time points via Ecological Momentary Assessment (EMA), totaling up to 28 assessments at each time point. All 28 assessments at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Positive affect will be assessed on a 1-7 Likert scale, with higher scores indicating higher positive affect.

Daily positive affect (composite of 9 positive affect items across 3 subscales: happiness (happy, pleased, and cheerful), calm (calm, at-ease, and relaxed), and vigor (lively, full-of-pep, and energetic), each assessed on a 1-7 Likert scale) assessed in daily life each evening for one week at two time points via end-of day diary, totaling up to 7 scores at each time point. All 7 composite scores at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher scores reflect higher positive affect.

State negative affect assessed in daily life four times per day for one week at two time points via Ecological Momentary Assessment (EMA), totaling up to 28 assessments at each time point. All 28 assessments at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Negative affect will be assessed on a 1-7 Likert scale, with higher scores indicating higher negative affect.

Daily negative affect (composite of 9 negative affect items across 3 subscales: anxiety (on edge, nervous, and tense), depression (sad, depressed, and unhappy), and hostility (hostile, resentful, and angry), each assessed on a 1-7 Likert scale) assessed in daily life each evening for one week at two time points via end-of day diary, totaling up to 7 scores at each time point. All 7 composite scores at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher scores reflect higher negative affect.

Number of social interactions assessed in daily life four times per day for one week at two time points via Ecological Momentary Assessment (EMA), totaling up to 28 assessments at each time point. All 28 assessments at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher numbers indicate more social interactions.

Number of social interactions assessed in daily life each evening for one week at two time points via end-of day diary, totaling up to 7 assessments at each time point. All 7 assessments at each of the two time points (pre-intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher numbers indicate more social interactions.

Mindful awareness (composite 3-item scale: "Today, I paid attention to what I was doing in the present moment" / "Today, I noticed body sensations come and go" / "Today, I noticed pleasant and unpleasant thoughts and emotions", each item assessed on a 1-7 Likert scale) assessed in daily life each evening for one week at two time points via end- of-day diary, totaling up to 7 scores at each time point. All 7 composite scores at each of the two time points (pre- intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher composite scores reflect higher mindful awareness.

Mindful acceptance (composite 2-item scale: "Today, I was able to step back and be aware of distressing thoughts, emotions, and sensations, without being taken over by them" / "Today, I did not want to feel the way I was feeling", each item assessed on a 1-7 Likert scale) assessed in daily life each evening for one week at two time points via end- of-day diary, totaling up to 7 scores at each time point. All 7 composite scores at each of the two time points (pre- intervention ambulatory assessment, post-intervention ambulatory assessment) will be averaged in MLM analyses. Higher composite scores reflect higher acceptance.

Assessed in-person via PROMIS Anxiety, a 4-item scale with raw scores ranging from 4-20 and converted to t-scores, with t-scores of 50 (standard deviation = 10) representing the average for the US general population and higher t- scores indicating higher anxiety

Assessed in-person via PROMIS Depression, a 4-item scale with raw scores ranging from 4-20 and converted to t- scores, with t-scores of 50 (standard deviation = 10) representing the average for the US general population and higher t-scores indicating higher depressive symptoms

Assessed in-person via Post-Traumatic Stress Disorder Checklist for Civilians (PCL-C), a 17-item scale ranging from 17-85, with higher scores indicating higher levels of trauma, and scores of 30 or greater indicating at least moderately severe PTSD symptoms

Assessed in-person via Cambridge Depersonalization Scale (a 29-item scale ranging from 0-116, assessing frequency and duration of depersonalization symptoms, with higher scores indicating greater depersonalization)

Assessed in-person via Perceived Stress Scale (a 10-item scale ranging from 0-40, with higher scores indicating higher perceived stress)

Assessed in-person via PROMIS Social Isolation, a 14-item scale with raw scores ranging from 14 to 70 and converted to t-scores, with t-scores of 50 (standard deviation = 10) representing the average for the US general population and higher t-scores indicating higher social isolation

Assessed in-person via Pittsburgh Sleep Quality Index (6-item short form, ranging from 0-12, with higher scores indicating worse sleep)

Assessed in-person via PROMIS Life Satisfaction, a 5-item scale with raw scores ranging from 5-35 and converted to t- scores, with t-scores of 50 (standard deviation = 10) representing the average for the US general population and higher t-scores indicating higher life satisfaction

Assessed in-person via PROMIS Positive Affect, a 15-item scale with raw scores ranging from 15-75 and converted to t-scores, with t-scores of 50 (standard deviation = 10) representing the average for the US general population and higher t-scores indicating higher positive affect

Assessed in-person via PROMIS Self-Efficacy, a 4-item scale with raw scores ranging from 4-20 and converted to t- scores, with t-scores of 50 (standard deviation = 10) representing the average for the US general population and higher t-scores indicating higher self-efficacy

Five Facet Mindfulness Questionnaire-Short Form (a 24-item scale including five subscales - observing, describing, acting with awareness, nonreactivity, and nonjudgment, with average scores ranging from 1-5 and higher scores indicating higher mindfulness)

Acceptance and Action Questionnaire-II (a 7-item scale ranging from 7-49, with higher scores indicating higher experiential avoidance)

Distress Tolerance Scale (a 15-item scale ranging from 1-5, with higher scores indicating higher distress tolerance)

Self-Compassion Scale (a 25-item scale ranging from 1-5, with higher scores indicating higher self-compassion)

Multidimensional Assessment of Interoceptive Awareness Scale (a 32-item scale comprised of eight subscales [Noticing, Not-Distracting, Not-Worrying, Attention Regulation, Emotional Awareness, Self-Regulation, Body Listening, and Trusting] ranging from 0-5, with higher scores indicating greater interoceptive awareness)