Heart Rate Variability as a Biomarker of Ageing

Heart rate variability (HRV) is the variation in time between successive normal heartbeats. Rather than treating a perfectly regular rhythm as optimal, HRV analysis quantifies the changing influence of autonomic and other regulatory processes on the sinoatrial node. [1]

Who This Is Useful For

This page is useful for readers evaluating physiological ageing measures, research using electrocardiography, or HRV estimates from wearable devices. It explains why HRV can contain information about autonomic function and health while remaining highly dependent on measurement context.

What Heart Rate Variability Measures

Time-domain measures include SDNN, which summarizes overall variation in normal-to-normal intervals, and RMSSD, which emphasizes short-term beat-to-beat changes. Frequency-domain analysis separates signal power into bands; high-frequency power is substantially influenced by respiration and cardiac vagal modulation, whereas low-frequency power has mixed physiological determinants and should not be treated as a simple measure of sympathetic activity. [1] [2]

Results from a short resting recording and a 24-hour ambulatory recording answer different questions. Recording duration, artefact correction, breathing, posture, and time of day must therefore be reported and standardized for meaningful comparison. [1] [3]

Why It Is Relevant to Ageing

Cross-sectional studies of healthy adults generally find lower total, low-frequency, and high-frequency power with increasing age, alongside reductions in several time-domain measures. The size and shape of the association differ by metric, and some measures appear to plateau in later adulthood rather than declining linearly throughout life. [4] [5]

These patterns are consistent with age-related changes in autonomic responsiveness, but chronological age is not the only determinant. Sex, cardiovascular and metabolic disease, physical fitness, sleep, medication, and environmental exposures can also influence HRV. Consequently, a lower value cannot be attributed to ageing alone. [4] [6]

Heart Rate Variability at a Glance

Association With Health Outcomes

Lower HRV has been associated with higher all-cause and cardiac mortality across healthy and patient populations. A 2022 meta-analysis covering 38,008 participants found broadly consistent associations across several HRV parameters, although the included populations and recording methods varied. [7]

Such findings establish prognostic association, not a single causal pathway. In cardiovascular disease cohorts, lower HRV is also associated with mortality and cardiovascular events, but effect estimates differ by disease group and analytical method. [8]

Measurement and Wearable Devices

Electrocardiography identifies electrical R waves and remains the reference method for deriving RR intervals. Many consumer devices instead use photoplethysmography to estimate pulse intervals. A systematic review found generally good agreement for classic measures at rest, with accuracy declining as exercise intensity increased. [9]

Device algorithms, sampling, missing-beat correction, and proprietary averaging can make values from different products non-equivalent. The literature on reference values in older adults also shows wide between-study variation and limited methodological standardization. [9] [10]

Evidence Quality and Interpretation

Confidence is moderate to strong that several HRV indices differ with age at the population level and that low HRV is associated with adverse outcomes. Confidence is lower that a single measurement can estimate an individual's biological age, because reference distributions overlap and acute conditions can shift the result. [4] [7] [10]

HRV is therefore best interpreted as a family of protocol-specific measures rather than one universal score. Longitudinal measurements made under comparable conditions may distinguish within-person change from some of the large differences between people, but they still do not isolate the cause of that change. [1] [3]

What This Does Not Mean

• It does not mean higher HRV is always better in every rhythm or clinical context.
• It does not mean HRV and resting heart rate are interchangeable.
• It does not mean one wearable reading can determine biological age.
• It does not mean values from different devices or protocols can be compared directly.

Practical Interpretation Examples

• If two studies report RMSSD: their values remain difficult to compare if posture, recording duration, breathing, or artefact processing differ.
• If HRV falls during acute illness: the change may reflect transient physiological stress rather than accelerated ageing.
• If a wearable reports a nightly trend: it is a device-specific estimate and should not automatically be treated as equivalent to clinical ECG-derived HRV.

Related Reading

• Heart Rate Recovery as a Biomarker of Ageing
• Digital Biomarkers in Longevity Research
• Categories of Ageing Biomarkers

Summary

Heart rate variability captures beat-to-beat cardiac timing and provides a non-invasive window onto autonomic regulation. Many indices decline with age and lower values are associated with adverse outcomes, but measurement sensitivity and biological non-specificity prevent HRV from functioning as a standalone ageing clock. [4] [7]

References

1. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. (1996). Heart rate variability: standards of measurement, physiological interpretation and clinical use. European Heart Journal, 17(3), 354-381. https://pubmed.ncbi.nlm.nih.gov/8737210/
2. Billman, G. E. (2013). The LF/HF ratio does not accurately measure cardiac sympatho-vagal balance. Frontiers in Physiology, 4, 26. https://pubmed.ncbi.nlm.nih.gov/23431279/
3. Laborde, S., Mosley, E., & Thayer, J. F. (2017). Heart rate variability and cardiac vagal tone in psychophysiological research: recommendations for experiment planning, data analysis, and data reporting. Frontiers in Psychology, 8, 213. https://pubmed.ncbi.nlm.nih.gov/28265249/
4. Umetani, K., Singer, D. H., McCraty, R., & Atkinson, M. (1998). Twenty-four hour time domain heart rate variability and heart rate: relations to age and gender over nine decades. Journal of the American College of Cardiology, 31(3), 593-601. https://pubmed.ncbi.nlm.nih.gov/9502641/
5. Kuo, T. B. J., Lin, T., Yang, C. C. H., Li, C. L., Chen, C. F., & Chou, P. (1999). Effect of aging on gender differences in neural control of heart rate. American Journal of Physiology, 277(6), H2233-H2239. https://pubmed.ncbi.nlm.nih.gov/10600841/
6. Tsuji, H., Venditti, F. J., Manders, E. S., et al. (1996). Determinants of heart rate variability. Journal of the American College of Cardiology, 28(6), 1539-1546. https://pubmed.ncbi.nlm.nih.gov/8917269/
7. Jarczok, M. N., Weimer, K., Braun, C., et al. (2022). Heart rate variability in the prediction of mortality: a systematic review and meta-analysis of healthy and patient populations. Neuroscience & Biobehavioral Reviews, 143, 104907. https://pubmed.ncbi.nlm.nih.gov/36243195/
8. Fang, S. C., Wu, Y. L., & Tsai, P. S. (2020). Heart rate variability and risk of all-cause death and cardiovascular events in patients with cardiovascular disease: a meta-analysis of cohort studies. Biological Research for Nursing, 22(1), 45-56. https://pubmed.ncbi.nlm.nih.gov/31558032/
9. Georgiou, K., Larentzakis, A. V., Khamis, N. N., Alsuhaibani, G. I., Alaska, Y. A., & Giallafos, E. J. (2018). Can wearable devices accurately measure heart rate variability? A systematic review. Folia Medica, 60(1), 7-20. https://pubmed.ncbi.nlm.nih.gov/29668452/
10. Rocha, A. S. L., Siqueira, V. B., Maduro, P. A., Batista, L. S. P., & Schwingel, P. A. (2024). Reference values for heart rate variability in older adults: a systematic review. Psychophysiology, 61(12), e14661. https://pubmed.ncbi.nlm.nih.gov/39073173/