A Digital Mindfulness Intervention to Improve Sleep Efficiency and Heart Rate Variability in Healthy Adults

A Digital Mindfulness Intervention to Improve Sleep Efficiency and Heart Rate Variability in Healthy Adults: A Randomized Waitlist-Controlled Trial

This study tested whether a 10-day smartphone app-based mindfulness program can improve sleep and reduce physiological stress in healthy adults. Eighty-one healthy adults were randomly assigned to either a mindfulness group (completing a daily 10-minute guided session via the Ōura app for 10 days) or a waitlist control group. All participants wore an Ōura Ring throughout the study to objectively measure sleep and heart rate variability (HRV). Questionnaires on perceived stress, sleep quality, burnout, and mindfulness were completed before, immediately after, and four weeks after the intervention. The study was conducted at the University of Southern Denmark.

Study Overview

• Status: Completed
• Conditions: Sleep; Heart Rate
• Intervention / Treatment: Behavioral: App-based mindfulness program (Headspace via Ōura app)

Detailed Description

This randomized controlled trial (RCT) used a waitlist-controlled design to examine whether a 10-day smartphone app-based mindfulness program could improve sleep and reduce physiological stress markers in healthy adults. The study was embedded within a broader 4-month longitudinal cohort study (N=140); the RCT sub-study focused on participants in the low-stress stratum (Perceived Stress Scale [PSS-10] ≤13) at screening. Participants (n=81) were randomized in approximately a 3:2 ratio to either a mindfulness intervention group (n=49) or a waitlist control group (n=32). The mindfulness group completed one 10-minute guided audio session daily ("destress" module, narrated by Headspace) delivered via the Ōura app for 10 consecutive days in free-living conditions at a time of their own choosing. Compliance was monitored objectively via app-recorded session timestamps. The waitlist control group wore the Ōura Ring and completed all questionnaires identically without receiving any intervention. All participants wore an Ōura Ring Gen 3 throughout the study to objectively and continuously measure sleep architecture, sleep efficiency, and heart rate variability (HRV). Self-report questionnaires on perceived stress (Perceived Stress Scale; PSS-10), sleep quality (Pittsburgh Sleep Quality Index; PSQI), burnout (Copenhagen Burnout Inventory; CBI), and mindful attention (Mindful Attention Awareness Scale; MAAS) were administered before, immediately after, and four weeks after the 10-day intervention period. The study was conducted at the University of Southern Denmark, Odense, Denmark.

• Study Type: Interventional
• Enrollment (Actual): 91
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Denmark
  • Odense, Denmark, 5230
    • University of Southern Denmark. Department of Psychology.

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Adults aged 20-60 years
• Body mass index (BMI) in normal range (18.5-29.9 kg/m²)
• Low stress at screening (Perceived Stress Scale (PSS-10) score ≤13)
• Willingness to wear the Ōura Ring continuously throughout the study
• No current regular mindfulness practice (defined as >20 min/week)
• Ability to provide written informed consent
• Sufficient Danish or English language proficiency

Exclusion Criteria:

• Current regular mindfulness or meditation practice >20 min/week
• Self-reported diagnosis of cardiovascular or neurodegenerative disease
• Current diagnosis of anxiety or depressive disorder
• Use of psychotropic medications, hypnotics, or medications affecting heart rate variability (HRV) or sleep
• Pregnancy
• Shift work or highly irregular sleep schedules
• Concurrent participation in another mindfulness or behavioral sleep intervention

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Mindfulness Intervention; Participants completed a 10-day app-based mindfulness program (one 10-min guided session/day via Ōura app) in free-living conditions.	Behavioral: App-based mindfulness program (Headspace via Ōura app); Participants completed one 10-minute guided audio mindfulness session daily ("destress" module, narrated by Headspace) delivered via the Ōura app for 10 consecutive days in free-living conditions at a time of their own choosing. Compliance was monitored objectively via app session timestamps.
No Intervention: Waitlist Control; Participants wore the Ōura Ring and completed all assessments without receiving any intervention.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Sleep Efficiency	Percentage of time asleep relative to total time in bed, measured continuously by Ōura Ring Gen 3 (accelerometry and photoplethysmography); computed as 7-day averages at each assessment timepoint.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Total Sleep Time	Minutes asleep per night, measured by Ōura Ring Gen 3.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Deep Sleep Duration	Minutes of slow-wave sleep per night, measured by Ōura Ring Gen 3.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Light Sleep Duration	Minutes of non-rapid eye movement (NREM) light sleep per night, measured by Ōura Ring Gen 3.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Sleep Onset Time	Clock time of sleep onset, measured by Ōura Ring Gen 3.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Heart Rate Variability (HRV)	Root mean square of successive differences (RMSSD) (ms) measured during 10-min mindfulness sessions compared to an equivalent pre-session baseline period, assessed by Ōura Ring Gen 3.	Daily during 10-day intervention period
Perceived Stress Scale (PSS-10)	Perceived Stress Scale (PSS-10). Self-report questionnaire; sum score 0-40.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Pittsburgh Sleep Quality Index (PSQI)	Pittsburgh Sleep Quality Index (PSQI). Self-report questionnaire; global score 0-21.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Copenhagen Burnout Inventory (CBI)	Copenhagen Burnout Inventory (CBI). Self-report questionnaire; subscale scores 0-100%.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10); 4-week follow-up (Time 2: days 22-28 of follow-up)
Mindful Attention Awareness Scale (MAAS)	Mindful Attention Awareness Scale (MAAS). Self-report questionnaire; sum score 15-90. Administered to the mindfulness intervention group only.	Pre-intervention (Time 0: 7-day average immediately before Day 1); post-intervention (Time 1: 7-day average immediately after Day 10)

Collaborators and Investigators

• Sponsor: University of Southern Denmark
• Investigators: Principal Investigator: Ulrich Kirk, PhD, University of Southern Denmark

Study record dates

Study Major Dates

• Study Start (Actual): December 1, 2023
• Primary Completion (Actual): May 1, 2024
• Study Completion (Actual): August 1, 2024

Study Registration Dates

• First Submitted: March 3, 2026
• First Submitted That Met QC Criteria: March 10, 2026
• First Posted (Actual): March 13, 2026

Study Record Updates

• Last Update Posted (Actual): March 13, 2026
• Last Update Submitted That Met QC Criteria: March 10, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Mindfulness; Heart Rate Variability; Sleep Efficiency
• Other Study ID Numbers: 21345

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data will be made available from the corresponding author (Ulrich Kirk; ukirk@health.sdu.dk) on reasonable request. Data sharing will comply with the Danish Data Protection Act and General Data Protection Regulation (GDPR) (Regulation EU 2016/679).
• IPD Sharing Time Frame: Following publication of primary results
• IPD Sharing Access Criteria: Data available upon reasonable request to the corresponding author.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No