HEALTHHeart Rate Variability and Health

Heart Rate Variability and Health

By: Howard LeWine, M.D., Harvard Health Publishing

Q: What does heart rate variability mean and how is it related to our health?

A: Heart rate variability (HRV) is a measure of the variation in time between each heartbeat. We know that a heart rate that’s too slow, too fast, or irregular can signal a problem, so it’s only natural to think that a steady, regular pulse is a sign of a healthy heart. But for HRV, multiple studies suggest that having a high number is more likely to be associated with better health.

A highly variable heartbeat means that the interval between beats fluctuates, although only by a fraction of a second. For example, if your heart rate is 60 beats per minute, instead of one second between beats, you’d have 0.8 seconds between some beats and 1.2 seconds between others.

Heart rate variability is controlled by a primitive part of the nervous system called the autonomic nervous system (ANS). The ANS works behind the scenes, automatically regulating our heart rate, blood pressure, breathing, and digestion among other key tasks. The ANS is subdivided into two large components: the sympathetic and the parasympathetic nervous system, also known as the fight-or-flight mechanism and the relaxation response.

A high HRV seems to signal a healthy heart, because it reflects the heart’s ability to respond quickly to rapid changes occurring throughout the body. In a healthy person, HRV should increase when your heart rate drops, as it does during relaxing activities such as reading or meditating. HRV decreases as the heart rate rises, such as when you exercise or are under stress.

In fact, HRV changes constantly, both throughout the day and from day to day. But chronic stress, poor sleep, lack of exercise, and an unhealthy diet can disrupt the balance, and your fight-or-flight system can shift into overdrive.

Low HRV is associated with an increased risk of cardiovascular disease. People with high HRV, on the other hand, tend to have higher fitness levels and be more resilient to stress. However, there isn’t a recommended HRV value because it varies widely, depending on your age, sex, fitness level, medical history, and genetics.

Many smart watches and wearable health monitors feature programs that measure HRV, though it’s not clear just how accurate or reliable these readings are. While HRV has been linked to overall physical fitness, the correlation between changes in HRV and how your autonomic nervous system is functioning will require much more research. Still, if you decide to use HRV as another piece of health data, do not get too confident if you have a high HRV, or too worried if your HRV is low.

(Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.)

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