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Heart Rate Variability: What It Reveals About Your Health

I’ve been hearing a lot about heart rate variability (HRV). It appears to be yet another buzzword in the world of health, fitness, and wellness, but what is it? What does it mean? Is this something we should all get checked and measured? If so, how do we measure it? I had so many questions, so I wrote this week’s blog on HRV to provide the answers.

What is Heart Rate Variability (HRV)?

We often think of our heartbeat as a regular, rhythmic, and fixed lub-dub, lub-dub, lub-dub, etc. That is not what actually happens. Our hearts are not metronomes, and beats do not occur at exactly timed intervals. There is a small measure of change between each of those heartbeats that is dependent on so many different contributing factors. That change in intervals between each of the heart beats is called heart rate variability (HRV).1 The interesting part about HRV is that it gives additional insights into our autonomic nervous systems. In order to really understand HRV, we need to break for a second to discuss the autonomic nervous system.

What is an Autonomic Nervous System?

We have two systems that contribute to our peripheral nervous system: the somatic nervous system and the autonomic nervous system. The somatic nervous system is our voluntary system, meaning it is the one you can control – move your arm, take a deep breath, get up and walk. Our autonomic nervous system controls things like digestion, heart rate, and respiratory rate. The autonomic nervous system is made up of the parasympathetic and sympathetic nervous systems. The parasympathetic slows our heart rate, lowers our blood pressures, and helps us digest our food, among other things. The sympathetic nervous system is the yin to the parasympathetic yang. It speeds up our heart rate, increases our blood pressure, and helps us with our fight-or-flight response. Neither system is better than the other. They work together to keep our bodies regulated and adaptable. HRV reflects how this system is working and can give insights to our bodies because there are many conditions that can affect our autonomic nervous systems.

System

Contributors/Conditions

Neurologic

Traumatic brain injury, cerebrovascular diseases, epilepsy, neurodegenerative diseases, Guillain-Barré syndrome, hereditary leukoencephalopathies, prion disorders, peripheral neuropathy, paroxysmal sympathetic hyperactivity.2-5 

Autoimmune/Inflammatory

Autoimmune autonomic ganglionopathy, Sjögren syndrome, paraneoplastic syndromes, fibromyalgia, chronic fatigue syndrome, other autoimmune diseases.5-7

Metabolic

Diabetes mellitus, amyloidosis, perimenopause/menopause, thyroid disease, endocrine disorders, vitamin deficiency, porphyria, dehydration.5,6,8

Infectious/Toxic

Botulism, tetanus, exposure to neurotoxins, chemotherapy, alcohol withdrawal, long COVID, HIV.2,6,7

Cardiac

Postural orthostatic tachycardia syndrome (POTs), neurocardiogenic syncope9,10

Lifestyle factors

Physical inactivity, poor diet, obesity, chronic psychological stress, sleep deprivation, smoking, and excessive alcohol use.11-20

 

How HRV Reflects Your Overall Health

Heart rate and how well the heart squeezes are modulated by the autonomic nervous system.21 In healthy conditions, the sympathetic nervous system is more dominant, and the parasympathetic counters it to slow things down. There are continuous physiological variations in a balanced system. When dysregulated, the parasympathetic nervous system has a decreased ability to influence the sympathetic nervous system and thus there is not as much variation.21 This is where HRV comes into play. Variability between our heartbeats means our autonomic nervous system is balanced. So, a higher HRV is indicative of better overall health and a balance within our autonomic nervous system.

Studies have linked HRV to cardiovascular and overall health. A meta-analysis looking at the relationship between HRV and cardiac events found that low HRV was associated with an increased risk of a cardiac event in individuals without any known history of cardiovascular disease.22 Another meta-analysis supported the finding of increased risk for cardiac events with low HRV, in addition to an increased all-cause mortality in people with a low HRV.23 A smaller study found an increased risk of sudden cardiac death with low HRV and a rise in risk with incremental decreases in HRV.24

How Is Heart Rate Variability Calculated?

I’ll spare you the detailed math and algorithms and cut to the chase. An electrocardiogram (ECG) is the gold standard for measuring heart rate variability. There is some debate over which mathematical model is the best, how patients are positioned during a measurement, and the best duration of time to obtain a measurement, but none of that is for you to worry about.1,21,25 What you do need to know about is the HRV output of your wearable devices.

I own two separate wearable devices that offer a long list of data and metrics. HRV is offered on both, and there is about a 20-point difference between the two readings. One reason is because most consumer wearables use photoplethysmography (PPG) rather than ECG to estimate HRV. There are some issues with PPG measurements. PPG signal quality varies and sometimes data points do not get recorded.26-29 This leads to an underestimation of true HRV values. For example, the Apple Watch systematically underestimates HRV compared to ECG.30

Another reason for this difference is the mathematical algorithm used to obtain HRV varies between the devices. Not to get technical, but some devices use the SDNN method and some use RMSSD method. Again, nothing we need to cover in great detail, but if you’re curious, you can look this up and read about it more.1 This doesn’t mean you should throw these values out the window. They still provide useful information, which we will discuss.

Normal HRV Ranges: Why “Average” Doesn’t Mean the Same for Everyone

As is the case with many biometric measurements, HRV depends on age, sex, race, level of fitness, diet, and sleep, so whether an HRV is normal or not is dependent on context. Several papers have examined normal HRV values for sex and age. Unfortunately, many of them use different durations of time, different calculation methods, and some use non-ECG based measurements. There are no standardized benchmarks for HRV, but I wanted to provide some general ranges identified in a couple studies.

Percentile values of HRV using a 5 minute ECG RMSSD method31-35

Age Group

Sex

25th

50th

75th

95th

20–30

M

24

34

48

68

20–30

F

26

36

50

70

35–44

M

22

32

45

60

35–44

F

24

34

48

65

45–54

M

19

28

39

52

45–54

F

21

30

42

56

55–64

M

16

25

35

46

55–64

F

17

27

38

50

65–74

M

14

22

32

40

65–74

F

15

24

34

44

Again, these are not standardized benchmark values. The only value that I consider actionable is an HRV in the 25th percentile or lower because it is associated with a higher risk of cardiac events and all-cause mortality.

Improving Your HRV: What the Evidence Shows

You are going to call me a broken record, but the fact is that lifestyle plays a huge role in HRV. Regular physical activity, relaxation techniques, biofeedback, sleep, and nutrition influence HRV.

Regular exercise including aerobic, resistance, and high-intensity interval training consistently increases HRV across a range of populations, including healthy adults and those with cardiovascular disease. Exercise enhances parasympathetic tone and reduces sympathetic activity, which are key mechanisms for increasing HRV.36,37

 Relaxation therapies such as progressive muscle relaxation, meditation, yoga, and controlled slow breathing have also been shown to increase HRV. Progressive muscle relaxation performed several times per week can significantly improve HRV over time.38 The only part of your autonomic nervous system that you can control is your breathing. Techniques like biofeedback, which help individuals consciously regulate breathing and autonomic responses, are effective in increasing HRV, especially in patients with coronary artery disease.38 Breathing at an individualized resonance frequency may maximize HRV benefits, but this frequency can vary over time and should be assessed before each session.39 Mindfulness and meditation can further enhance voluntary upregulation of HRV, especially when combined with biofeedback.40,41

 Weight reduction, diets rich in whole foods, and restorative sleep are also associated with a higher HRV.42-44

The Bottom Line: HRV as a Useful but Imperfect Health Metric

HRV is a valuable data point and a useful marker of overall health but interpreting it requires some nuance. The absolute number in isolation offers limited insight because there’s no universal benchmark for comparison. What’s more meaningful is your personal trend over time. Whether your HRV is measured in-office via ECG, at home over 24 hours, or through a wearable device, the key is to establish your own baseline. If you notice a sudden decrease, it’s worth asking some questions: How are you sleeping? What are your stress levels like? Have your eating or exercise habits changed?

I can give you a personal example. As I write this, I’m traveling to speak at a conference, and my HRV is noticeably lower than usual, but I also know why. I’m not sleeping as well, my diet is off, I’ve had a couple of drinks (something I rarely do), and I’m a little anxious about presenting, even though I’ve done it countless times. If I saw a similar dip at home, I’d run through the same checklist and adjust what I could identify as a contributing factor.

However, if someone’s HRV drops and stays low despite addressing lifestyle factors, that’s when it’s worth checking in with a physician for a clinical HRV assessment via ECG and possibly a broader medical workup.

From a physician’s perspective, I find HRV valuable in two main scenarios. First, as a longevity metric. When a patient’s HRV is low, I can use it as a starting point to create a personalized plan to improve it, since higher HRV is linked with better health outcomes and longevity. Second, when a patient’s HRV falls at or below the 25th percentile, it prompts a deeper evaluation for potential medical conditions associated with dysautonomia (see first table).

I’m actually in the market for an ECG machine capable of 5-minute HRV readings because, after all the research I’ve done, I see the value in tracking and trending this metric for my patients over time.

Disclaimer: Even though I’m a doctor, I’m not your doctor—and reading this blog does not establish a doctor–patient relationship. This information is intended for general educational purposes only and should not be taken as personalized medical advice. Always speak with your own healthcare provider before making decisions about your health.

References

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