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Heart rate variability (HRV) and resilience

Heart Rate Variability — what each study measured, and what your watch measures

What heart rate variability studies measured, versus what your own watch measures, by instrument, measurement window, index, endpoint and result.
InstrumentStudy, endpoint and result
ECG
5 min · RMSSD
Jarczok et al. 2022
all-cause mortality
HR 1.56 (1.32-1.85), unadjusted
ECG rhythm strip (ARIC)
2 min · HRV
Dekker et al. 2000
all-cause and CHD mortality
no ratio in our record
fingertip PPG
SDNN
Saito et al. 2025
all-cause mortality
HR 1.51 (1.15-1.98)
ECG (Rotterdam)
10 sec · SDNN
de Bruyne et al. 1999
cardiac mortality
HR 1.8 (1.0-3.2)
—
device not in our record · LF power
Tsuji et al. 1994
all-cause mortality
HR 1.70 (1.37-2.09)
chest-worn ECG (ActiHeart)
multiday · SDNN proxy
Schaarup et al. 2025
all-cause mortality
incidence rate ratio 0.79 (0.66-0.94)
wrist PPG (consumer wearable)
overnight · RMSSD
your watch
—
no study on record

What it is

HRV is the beat-to-beat variation in your heart rhythm — a marker of autonomic nervous system balance. Recovery-focused wearables report it nightly.

Why it matters for longevity

Across 32 studies covering over 38,000 people, lower HRV predicted higher mortality. The headline HR 1.56 is the UNADJUSTED comparison of the lowest quartile of 5-minute ECG RMSSD versus the other three quartiles — not wearable nightly HRV. As of 2026-08-29 this calculator's curve uses the paper's smaller covariate-adjusted estimate (~1.23) instead. The measurement mismatch remains: users enter overnight wearable RMSSD. Saito 2025 (fingertip PPG, 5-min sitting rest) and Schaarup 2025 (ActiHeart chest ECG, multi-day SDNN) are nearby but not that construct — no all-cause HR for overnight consumer-wrist RMSSD has been found.

How to improve it

  • Improve sleep quantity and regularity
  • Train aerobically but respect recovery
  • Practice slow breathing; limit late alcohol

Evidence, by endpoint

EndpointGradeFinding
All-cause mortality (RMSSD lowest quartile)C
Bottom Quartile (Jarczok 2022)
Unadjusted, the lowest quartile of 5-minute ECG RMSSD had HR 1.56 vs the other three quartiles. This calculator uses the paper’s smaller covariate-adjusted estimate (~1.23).
All-cause mortality (overnight wrist RMSSD)X
Not overnight wrist RMSSD
Jarczok is 5-minute ECG. Saito 2025 is 5-minute fingertip PPG; Schaarup 2025 is chest-ECG multi-day SDNN. No all-cause HR for overnight consumer-wrist RMSSD has been found.
All-cause mortality (per 1-SD lower LF power)B
1.70x per SD of LF Power (Tsuji 1994)
Framingham: in 736 elderly adults (mean age 72) followed 4 years, each 1-SD lower low-frequency HRV power carried ACM HR 1.70 (1.37–2.09), independent of traditional risk factors — a different metric again (LF power), and different from the overnight wearable RMSSD users actually enter.
Cardiac mortality (SDNN quartile, U-shaped)C
U-Shaped, Not Just Low HRV (de Bruyne 1999)
Rotterdam Study measured heart-rate variability (SDNN) via a standard 10-second ECG in over 5,000 adults 55+: the lowest SDNN quartile carried 80% higher cardiac mortality than the middle quartile (HR 1.8, 95% CI 1.0–3.2) — but so, unexpectedly, did the highest quartile (HR 2.3, 95% CI 1.3–4.0), a U-shaped pattern the authors said needed further study.

What argues against this

No source in this set reverses the direction of the low-HRV-worse association outright, but de Bruyne 1999 (Rotterdam Study, >5,000 adults 55+) complicates the engine's implicit monotonic framing: the lowest SDNN quartile carried 80% higher cardiac mortality (HR 1.8, 1.0–3.2) versus the middle quartile, but so did the highest quartile (HR 2.3, 1.3–4.0) — a U-shaped pattern suggesting very high HRV is not straightforwardly protective either. It measures cardiac mortality via 10-second ECG SDNN, not the all-cause mortality / 5-minute RMSSD construct Jarczok 2022 and this calculator use, so it disagrees on shape and construct, not sign.

Last reviewed 2 September 2026

Evidence

  1. Jarczok et al. (2022) — Neuroscience & Biobehavioral Reviews
    Heart rate variability in the prediction of mortality: a systematic review and meta-analysis
    View source
  2. Dekker et al. (2000) — Circulation
    Low heart rate variability in a 2-minute rhythm strip predicts risk of coronary heart disease and mortality from several causes: the ARIC Study. Atherosclerosis Risk In Communities
    View source
  3. Saito et al. (2025) — Circulation Reports
    Pulse Rate Variability and All-Cause Mortality Risk in the General Japanese Population
    View source
  4. de Bruyne et al. (1999) — American Journal of Epidemiology
    Both decreased and increased heart rate variability on the standard 10-second electrocardiogram predict cardiac mortality in the elderly: the Rotterdam Study
    View source
  5. Tsuji et al. (1994) — Circulation
    Reduced heart rate variability and mortality risk in an elderly cohort. The Framingham Heart Study
    View source
  6. Schaarup et al. (2025) — Diabetes, Obesity and Metabolism
    Cardiovascular autonomic dysfunction precedes cardiovascular disease and all-cause mortality: 11-year follow-up in the ADDITION-PRO study
    View source
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