What Is HRV and Why Does It Matter for Sleep? An Expert Weighs In
One overlooked metric that may affect your sleep is your heart rate variability. Here's the link between HRV and your sleep quality.
Scientists have a lot to learn about the connection between sleep and stress, but one thing is clear: They're both trending in the wrong direction. As revealed in a recent Gallup poll, the proportion of Americans saying they get enough sleep dropped from 55% to 42% over the past 20 years. During that same period, the percentage who say they frequently experience stress in daily life jumped from 33% to 49%.
Stress is only one factor that may contribute to poor sleep, and vice versa. Both issues can harm your health, and it's critical not to ignore the signs in either area. While many signals may point to sleep and stress concerns, one particular indicator may not be on your radar: heart rate variability.
HRV shows how well your body adapts to stress. It can be both an indicator of and contributor to your sleep quality and resilience in the face of daily challenges, so understanding what it is and how to influence it can help you take more control over your overall health.
What is heart rate variability?
HRV measures how much your heart rate fluctuates from beat to beat. For instance, if your pulse is 60 beats per minute, that's an average. Your heart isn't perfectly on pace, beating once every second on the dot; it changes slightly over time.
Heart rate variability is normal, even positive. HRV indicates how quickly your body responds to change and stressors, so a higher number is a good sign. Exactly how high depends on several factors -- most notably, HRV tends to decline with age -- but higher is generally better.
"High HRV reflects the body's ability to handle stressors," says Maggie Michalcyzk, a registered dietician and wellness expert. "The higher it is, that could indicate that you're a little more resilient at handling stress well."
Your heart rate is controlled by both sides of your nervous system. The sympathetic nervous system controls your "fight or flight" response, stimulating your heart and other organs to react quickly to danger so you can respond appropriately. The parasympathetic nervous system promotes relaxation and helps you calm down after such a reaction.
HRV is a function of the complex interplay between these two systems, demonstrating how adaptable you are to stressful situations.
The connection between HRV and sleep
Recent research has revealed that HRV is connected to more than just stress response. How quickly your heart rate fluctuates can be a powerful indicator of your sleep quality.
For instance, one study showed a correlation between poor sleep and higher resting heart rate, lower HRV and high blood pressure while asleep. Another study concluded that higher daytime HRV was connected to more efficient sleep. Enough of a connection has been observed that low HRV is now used as a screening tool for potential sleep disorders like insomnia and sleep apnea.
Overall, the research indicates there's a mutually beneficial relationship at play. The better your sleep, the healthier your HRV. The healthier your HRV, the better your sleep. Michalcyzk notes that this is likely due to other aspects of mental and cardiovascular health that a higher HRV reveals.
How to increase your HRV
Whatever the nuances of this interplay between HRV and sleep, it's clear that improving HRV can lead to better sleep quality, which can further improve HRV. Although average HRV declines with age, there are ways to increase it regardless of your stage in life.
How do you start that cycle? Here are a few changes Michalcyzk recommends to boost your HRV.
Improve your eating habits
Diet has long been demonstrated to play an important role in cardiac health, and there is specific evidence it can improve HRV. A Mediterranean diet, which is heavy in vegetables, fruits, herbs, nuts, beans and whole grains, along with moderate dairy, poultry and eggs, has been correlated with higher HRV.
One recent study even highlighted the benefits of one nut in particular: almonds. When participants under stress snacked on whole almonds for six weeks, they saw an increase in their HRV compared to the control group. Researchers theorize this may be due to the high magnesium content in almonds.
The takeaway? To boost your HRV, add more tree nuts, vegetables, whole grains and similar heart-healthy foods to your diet.
Exercise
Exercise is also strongly associated with cardiovascular health, and has been associated with improved HRV and better sleep quality. The American Heart Association recommends that adults get at least 150 minutes of moderate physical activity or 75 minutes of intense physical activity per week.
If you currently live a sedentary lifestyle, don't start with those goals; work your way toward them gradually. You can begin with a brisk walk a few times a week.
Practice mindfulness
Michalcyzk also notes how developing more mindful habits can improve your ability to relax and calm down from stress, which can improve your HRV.
This could involve any number of different practices. You may prefer journaling, breathing exercises or spiritual practices like meditation or prayer. Or, you might set a daily time to disconnect from electronics and read. Whatever your mindful habits, the idea is to slow your mind down and strengthen your mental resilience.
Read more: Best Meditation Apps to Reduce Stress
Prioritize sleep hygiene
Improving your sleep quality, and in turn, your HRV also involves changing some aspects of your sleep routine and environment, which includes things like the temperature of your room, lighting and electronics by the bed, as well as keeping a consistent sleep/wake time and winding down before bed.
Michalcyzk also emphasizes how eating habits contribute to sleep hygiene. Spreading your food intake evenly throughout the day, rather than saving your biggest meal for close to bedtime, is particularly important.
"A more consistent eating pattern throughout the day can definitely support sleep quality," she says.
Monitoring changes in your HRV
If you're trying to raise your heart rate variability, the natural question is how closely you should track it. Nowadays, this is fairly easy with smartwatches and other fitness trackers with built-in monitoring capabilities for HRV and other important data points.
"In general, people can track their HVR to plan workouts and monitor stress levels," Michalcyzk says. "For most healthy adults, using an at-home tracker works. If you're tracking via your Apple Watch or a home device and notice a big change, this is something to chat with your doctor about."
Still, in most situations, HRV isn't something you need to monitor closely. During times of stress, it may be an important indicator you can use to support lifestyle changes and protect your health.
"For people who feel that they are in a time of high stress," says Michalcyzk, "it may be an interesting piece of data to have to help them better support their sleep quality, better support mindfulness practices that can help lower stress in general."
The bottom line
Heart health and sleep are intricately connected; the more you improve one, the more you enhance the other. HRV is a small but significant signal that stress may be throwing your health and sleep off balance. If you notice yours is low or has been declining, you can adjust your diet, exercise, mindfulness practices and sleep habits to get it back on track. Most importantly, always discuss your heart health and sleep habits with your doctor.