Heart rate variability: what is normal for your age?

In a healthy adult, heart rate variability (HRV) measured at rest over 5 minutes averages 42 milliseconds for the RMSSD index, with a usual range of 19 to 75 ms. This figure drops markedly with age: a woman aged 25 to 34 averages 43 ms, a woman aged 65 to 74 about 19 ms. Here are the values by age group and sex, the right way to measure it, what makes it rise or fall, and what large cohorts say about its link with cardiovascular risk.

Heart rate variability: definition and units of measurement

HRV refers to the beat-to-beat fluctuation of the time interval between two contractions of the heart. A heart beating at 60 bpm does not beat exactly every 1,000 milliseconds: one interval lasts 980 ms, the next 1,030 ms, then 1,005 ms. Cardiologists and researchers use the abbreviation HRV, while French clinicians call it VFC.

High HRV signals a responsive heart, able to speed up and slow down quickly with breathing, posture or effort. Low HRV reflects a more rigid rhythm, often dominated by the sympathetic system, the system of alertness and stress. Resting heart rate and HRV are therefore two distinct pieces of information: two people at 65 bpm can have very different variability.

The 1996 report of the joint European and North American Task Force set the calculation methods still used today (Task Force ESC/NASPE, 1996). Three indices dominate practice, alongside one ratio whose meaning is now debated:

• RMSSD, the root mean square of successive differences, expressed in ms: it is the index used by smartwatches and the best reflection of vagus nerve activity.
• SDNN, the standard deviation of all normal intervals, in ms: over 24 hours, it remains the reference for estimating cardiac risk.
• High-frequency power, or HF (0.15 to 0.40 Hz), in ms², linked to breathing and parasympathetic activity.
• The LF/HF ratio, long presented as an index of the balance between the sympathetic and parasympathetic systems, whose interpretation is now disputed.

What makes the heart rhythm vary from beat to beat

The vagus nerve is the main driver of HRV at rest. This parasympathetic nerve constantly brakes the sinus node, the heart’s natural pacemaker located in the right atrium. Its action is very fast, taking less than a second, which allows it to change the length of each individual beat. The sympathetic system acts more slowly, over several seconds, and tends to smooth out the rhythm.

Several mechanisms overlap in everyday life:

• Respiratory sinus arrhythmia: the heart speeds up when you breathe in and slows down when you breathe out, which explains the effect of slow breathing.
• The baroreflex, which adjusts heart rate to changes in blood pressure roughly every 10 seconds.
• The circadian rhythm, with higher HRV at night, especially during deep sleep.
• Thermoregulation and the renin-angiotensin system, which shape the slow oscillations visible over 24 hours.

With aging, vagal tone declines, the sinus node responds less well to nerve signals and the arteries stiffen, which blunts the baroreflex. This loss of flexibility in the communication between the brain and the heart explains why HRV falls with age, independently of any disease.

Normal heart rate variability by age and sex: what the science says

The quantitative review by Nunan and colleagues remains the reference for adults: 44 studies published between 1997 and 2008, covering 21,438 healthy participants (Nunan et al., 2010). On a 5-minute resting recording, mean RMSSD is 42 ms (standard deviation 15, range 19 to 75 ms) and mean SDNN is 50 ms (range 32 to 93 ms). These values are lower than those of the 1996 report, which relied on smaller samples.

For the effect of age, the most detailed short-recording study comes from the KORA S4 cohort in Bavaria: 1,906 adults without heart disease, 782 women and 1,124 men, recorded for 5 minutes lying down (Voss et al., 2015).

The standard deviations are wide: at 50, an RMSSD of 15 ms and one of 40 ms both fall within the statistical norm. Women show a slightly higher RMSSD and a weaker sympathetic component than men, but these differences disappear after 55. The 65-74 decade no longer shows a significant decline compared with the previous one.

Over 24 hours, the Umetani study (260 people aged 10 to 99) describes the same trajectory. RMSSD falls by the fifties to 47% of its value measured between ages 10 and 19, then levels off. SDNN, for its part, declines more slowly and reaches 60% around age 90 (Umetani et al., 1998). Wearable data confirm this profile on a large scale: among 8,203,261 Fitbit users, HF power drops by 82% between ages 20 and 60 in men (Natarajan et al., 2020).

Low heart rate variability: what link with cardiovascular risk?

Low HRV is associated with a higher risk of cardiovascular events, including in people with no known disease. The Hillebrand meta-analysis (8 studies, 21,988 participants) puts this excess risk at 35% for the lowest SDNN level compared with the highest (Hillebrand et al., 2013). Each 1% increase in SDNN corresponds to roughly 1% lower risk.

In older adults, the Framingham cohort followed 736 participants with an average age of 72 for 4 years, and 74 of them died. Each one-standard-deviation drop in LF power was associated with a 1.70-fold higher risk of death (Tsuji et al., 1994). After a heart attack, the landmark Kleiger study of 808 patients found 5.3 times higher mortality when 24-hour SDNN fell below 50 ms, compared with an SDNN above 100 ms (Kleiger et al., 1987).

These results are observed associations, not a cause-and-effect relationship. Low HRV can reflect early diabetes, high blood pressure, poor physical fitness or prolonged stress. The number serves as a warning sign about the state of the autonomic nervous system, not as a diagnosis. Cardiovascular diseases remain the leading cause of death worldwide according to the World Health Organization, which explains why researchers are so interested in a marker this easy to collect.

In practice: measuring and interpreting your heart rate variability

The measurement method changes the HRV you see more than age does from one decade to the next. A watch reading taken at night cannot be compared with a 5-minute daytime ECG, or with a 24-hour Holter. The review by Shaffer and Ginsberg stresses this point: 24-hour, 5-minute and under-5-minute norms are not interchangeable (Shaffer and Ginsberg, 2017).

With HRV, the best reflex is to compare yourself with your own baseline. A clear and lasting drop from your usual average after an infection, a short night or a hectic period says more than any comparison with a table. The link between stress and the autonomic nervous system is explained in our article on heart rate coherence, and the other number worth tracking at rest is covered in our guide to resting heart rate by age.

HRV is a matter of communication between organs, one of the hallmarks of aging presented on our pillar page on altered intercellular communication. Medical advice is warranted if a very low value comes with palpitations, shortness of breath, fainting spells or an irregular rhythm flagged by your watch.

How to preserve your HRV: evidence-based tips

Endurance exercise is the strongest lever for supporting HRV. The Routledge review reports that training increases HRV after a heart attack, in heart failure and after revascularization, through a rise in vagal tone (Routledge et al., 2010). In the Fitbit data, the higher the daily step count, the better the HRV, at every age and in both sexes.

Alcohol takes a heavy toll, even at low doses. Among 4,098 Finnish employees followed in real life, the HRV-derived recovery index during the first 3 hours of sleep fell by 9.3 points with low intake. The drop reached 24.0 points with moderate intake and 39.2 points with high intake (Pietilä et al., 2018). Regular physical activity did not protect against this effect.

Habits to build into your daily routine:

• Aim for at least 150 minutes of moderate activity per week, the threshold recommended for adults by the World Health Organization.
• Protect your sleep, especially deep sleep, the period when HRV peaks (see our tips to increase deep sleep).
• Limit alcohol, especially in the hours before bedtime.
• Practice a few minutes of slow breathing, at around 6 breaths per minute: a meta-analysis of 58 controlled trials finds a small to moderate benefit on anxiety, depression and performance (Lehrer et al., 2020).
• Always measure under the same conditions: on waking, sitting or lying down, before your coffee.

Thayer and colleagues link low HRV to several modifiable risk factors, including high blood pressure, high blood sugar and chronic stress (Thayer et al., 2010). Acting on these factors remains the priority, with HRV serving as a tracking indicator rather than a target in itself.

Frequently asked questions about heart rate variability

What is a normal heart rate variability at 60?

Between 55 and 64, the KORA cohort measures an average RMSSD of 21 ms in women and 20 ms in men, over 5 minutes at rest. Standard deviations exceed 11 ms, so most healthy people fall between roughly 10 and 33 ms. Watches that measure at night often display higher numbers than these daytime norms.

Why does HRV decline with age?

HRV declines mainly because the tone of the vagus nerve weakens over the years. The sinus node responds less to nerve signals and the baroreflex loses sensitivity as the arteries stiffen. The Umetani study shows RMSSD falling to 47% of its adolescent value by the fifties, then leveling off beyond that.

What is the difference between RMSSD and SDNN?

In HRV terms, RMSSD measures the differences between successive beats and mainly reflects the vagus nerve: it is the index used by watches and 5-minute measurements. SDNN measures the spread of all intervals and is best calculated over 24 hours. After a heart attack, a 24-hour SDNN below 50 ms was associated with 5.3 times higher mortality.

How can you increase your HRV naturally?

Regular endurance exercise is the best-supported lever, with a dose-response relationship in data from 8.2 million watch users. Drinking less alcohol in the evening, getting enough sleep and practicing slow breathing round out this foundation. The effects remain modest and vary from one person to another.

Is low heart rate variability dangerous?

Low HRV on its own is not a diagnosis. It is statistically associated with a cardiovascular risk roughly 35% higher in the Hillebrand meta-analysis, but it also varies with stress, an infection or a short night. A lasting drop accompanied by palpitations, shortness of breath or fainting spells warrants medical advice.