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Baseline insomnia severity modifies the association between sleep efficiency and next-day daytime HRV (RMSSD) in a predominantly healthy cohort

In a wearable-based dataset of 49 participants over 4 weeks, the interaction between CSD-style sleep efficiency and baseline Insomnia Severity Index (ISI) was positively associated with next-day daytime RMSSD (β=0.0060; 95% CI, 0.0023 to 0.0097; P=0.002). This suggests that individuals with higher baseline insomnia symptoms show a stronger positive coupling between sleep efficiency and next-day heart rate variability.

Last updated: Jul 27, 2026•0 RCTs•📖 Read as article →

Evidence Score

Evidence Score34/100
Human RCT☆☆☆☆☆
Meta-analysis☆☆☆☆☆
Mechanism★★★★★
Safety★★★★☆
Confidencelow

Study Evidence

Study 1. Insomnia severity modifies diary-based sleep-continuity and sleep-initiation associations with next-day daytime HRV in a real-world wearable dataset.

observational

Meng X, Cai M · Digital health (2026)

Participants: N/A
Duration: 4 weeks
Intervention: Baseline insomnia severity (measured by Insomnia Severity Index) as a modifier of sleep-diary metrics (sleep efficiency, sleep latency, WASO, sleep duration)
Outcome: Next-day daytime heart rate variability (RMSSD, natural log transformed)
Effect Size: β=0.0060 (95% CI, 0.0023 to 0.0097) for sleep efficiency × ISI interaction
Population: 49 participants from a publicly available wearable dataset, predominantly healthy with non-severe baseline insomnia symptoms (no participant met criteria for severe baseline insomnia)

Result:

PubMed: 42460158DOI: 10.1177/20552076261469378

Mechanism Graph

Baseline insomnia severity is measured using the Insomnia Severity Index
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Daily sleep efficiency is derived from Consensus Sleep Diary-style definitions
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Daytime HRV (RMSSD) is aggregated from 5-minute windows between 09:00 and 23:00
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Higher baseline ISI modifies the positive association between sleep efficiency and next-day RMSSD

Limitations

  • ⚠Higher-ISI estimates were based on few participants in the moderate-ISI range and on person-days meeting daytime HRV coverage criteria
  • ⚠Findings should not be extrapolated to populations with severe or clinically diagnosed insomnia
  • ⚠Secondary analysis of a publicly available dataset with potential selection bias

Frequently Asked Questions

What is the primary finding of this study?▼

The study found that baseline insomnia severity modifies the association between sleep efficiency and next-day daytime heart rate variability (RMSSD), with a positive interaction (β=0.0060).

How was sleep efficiency measured?▼

Sleep efficiency was operationalized using a Consensus Sleep Diary (CSD)-style definition that explicitly incorporated wake after sleep onset (WASO).

What population was studied?▼

The study included 49 participants from a publicly available wearable dataset, with predominantly non-severe baseline insomnia symptoms; no participant had severe baseline insomnia.

What were the key limitations of the study?▼

Key limitations include small sample size for higher-ISI estimates, reliance on person-days meeting HRV coverage criteria, and inability to generalize to severe or clinically diagnosed insomnia populations.

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References

  1. 1.Meng X, Cai M. "Insomnia severity modifies diary-based sleep-continuity and sleep-initiation associations with next-day daytime HRV in a real-world wearable dataset.." Digital health, 2026. PMID: 42460158 DOI: 10.1177/20552076261469378
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