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The Relationship Between HRV and Sleep

As a human being, you’ll spend up to a third of your entire life sleeping.

If you don’t think something that requires this much time is essential, you are missing out on a massive part of what it means to be healthy!

Sleeping is a fundamental process that enables your body to attain a deep state of rest that helps organs function at their best. It also helps the body maintain behavioral, cognitive, and physical functionality.

The relationship between sleep quality and heart rate variability is a topic that has been extensively researched

What is HRV? 

What is HRV

Heart rate variability isn’t simply a measurement of your heartbeat. Instead, it’s a more in-depth expression of how well your body can adapt. HRV is a measurement of the variation in time between each heartbeat.

This variation in heart rate happens because of your autonomic nervous system, which is the system in your body that coordinates processes outside of your conscious control. Your autonomic nervous system regulates your parasympathetic and sympathetic nervous systems. These work together to regulate your blood pressure, organs, brain chemistry, and respiratory and digestive systems.

The autonomic nervous system (ANS) can be broken down into two subsystems, the sympathetic and parasympathetic nervous systems. The sympathetic nervous system controls your “flight-or-fight” responses and helps your body survive. Meanwhile, the parasympathetic nervous system enables you to relax.

HRV can provide a detailed look into how the two branches of the autonomic nervous system are regulated. When one side of the system becomes overburdened, there’s often a reduced variability in heart rate. Think of it like this: more action is distributed between the two systems when there is more variability, demonstrating even activation and not a one-sided affair. 

When the autonomic nervous system is out of balance, the sympathetic nervous system can exceed its boundaries, affecting the body in numerous ways represented by a low HRV score.

A healthy heart is not a constant metronome. 

The rhythms of your heart can and should vary as your body adapts to the exposure to daily stimuli. A low HRV score has been associated with depression, anxiety, and even increased chances of heart disease. Watching your HRV can help you track your emotional and behavioral well-being alongside your physical health and give you a clear picture of the quality of sleep and rest your body is getting. 

Why Sleep is So Important 

HRV and Sleep

Sleep is essential to every process in the body, affecting our physical and mental functioning, ability to fight disease, develop immunity and metabolism, and chronic disease risk. 

Getting plenty of sleep is essential for the body’s recovery due to its effects on the ANS. An improvement in HRV levels represents relief from an overly stimulated sympathetic nervous system and an improved ability to get deeper sleep.

We view sleep as a time of rest for the body, but a lot is happening beneath the surface. The brain is engaged in several activities necessary to cultivate a healthy body and mind and improve quality of life.

A healthy amount of sleep is vital for “brain plasticity,” or the brain’s ability to adapt to input. If we sleep too little, we cannot process what we’ve learned during the day, and we have more trouble remembering it in the future. Researchers also believe that sleep may promote removing waste products from brain cells, which seems to occur less efficiently when the brain is awake.

When you sleep, you go through different phases. The first stage is awake and falling asleep. The second is light sleep when heart rate and breathing regulate. The third and fourth stages are deep sleep. 

REM sleep used to be thought of as the most crucial sleep phase for learning and memory. However, newer data suggests that non-REM sleep is more important for these tasks and the more restful and restorative sleep phase.

The cycle repeats itself, but with each cycle, you spend less time in the deeper stages of sleep and more time in REM sleep. You’ll typically cycle through about four or five times on average.

Studies have confirmed that sleep deprivation can negatively affect your cardiovascular system and may be associated with an increased risk for hypertension due to increased sympathetic nervous system stimulation. On top of that, poor health due to excessive stress levels, poor diet, and a lack of exercise can contribute to less deep, restful states of sleep and, therefore, less healing and maintenance, which is key to excellent health and longevity. Due to the relationship to the autonomic nervous system here, we can see that HRV is negatively affected by poor sleep.  

Throwing off the natural rhythm of your heartbeat and nervous system activation creates a significant risk factor for cardiovascular diseases. HRV abnormality and sleep deprivation are risk factors for morbidity and chronic disease, making your sleep patterns a critical part of staying healthy. 

Many of us feel tired and unrested on days we thought we slept for “long enough.” It’s more important to focus on sleep quality and how rested you feel on a week-to-week basis rather than daily.

HRV and Sleep

Heart rate variability is a metric that can help you understand how well you’re sleeping. As you cycle through the different stages of sleep, your heart rate variability changes to the specific activity of each stage of sleep. The relationship between HRV and sleep rests on the link between the changes in heart rate associated with the shifts between the different stages of sleep. 

So, if your HRV is higher, it is a good sign that your body is going through all the proper sleep stages according to your body’s needs. 

Two main processes regulate the quality of your sleep: your circadian rhythm and your sleep drive. 

A biological clock located in the brain controls circadian rhythms. One key aspect of this clock is how it responds to light cues. A lack of light exposure increases the production of the hormone melatonin at night. When the brain senses light, the production stops. People with total blindness often have trouble sleeping because they can’t tap into their natural sleep-inducing system.  

To get more restful sleep, you need to experience healthy light exposure and go to sleep/wake up at similar times each day. These changes result in increased HRV levels, which can help you see the benefits of your efforts towards adopting a healthy sleep habit. This habit results in both physical changes and improved repair capabilities that occur during the different stages of sleep. 

Sleep drive also plays a key role: Your body craves sleep as it hungers for food. Throughout the day, as you expend energy, your body keeps track. As your body can repeat the cycle, it takes less energy to “switch up the program,” allowing for more focus on maintenance and longevity. 

Similarly, there is some evidence that your HRV during the day can indicate how well you sleep at night. If you exercise, eat well, take care of your mind, and manage stress, your heart will be more variable throughout the day, contributing to improved HRV and the ability to transition into rest. 

Stress is also a critical factor that has been considered a risk of sleep disturbances and thus may affect autonomic function during sleeping and influence HRV. Previous studies have presented that acute stress can cause autonomic dysfunction during sleep due to poor modulation between the sympathetic nervous system and the rest and digest response. Healthy people facing stressful conditions struggle with modulating between REM and non-REM phases of their Sleep. 

One study assessed the occurrence of sleep disturbances among males who had sleep apnea. The males presented a pattern of vagal imbalances resulting from sleep imbalances, parasympathetic loss during sleep, and decreased HRV. They concluded that reduced HRV is independent of underlying obstructive sleep apnea. Reduced HRV also accompanies higher morbidity and mortality

How To Get Better Sleep 

Ways to Improve Your Sleep

Now that we see how important sleep is for our health, let’s look at some of the most important ways to improve your sleep quality, ensuring that you’re getting deep, restful sleep.

Stick to a Schedule

Adhering to a regular sleeping schedule keeps your circadian rhythm in sync and improves deep, restful sleep states. 

Light Exposure

Exposure to sunlight in the morning and the transition to darkness at night will help cue hormonal processes that trigger your body’s ability to rest and transition into sleep. 

Minimize screen (blue light) exposure when first waking or within one hour of sleep to ease stimulation of the eyes and enable the brain to experience more deep, restful sleep stages.  

Get Into a State of Mind of Rest 

Doing simple acts that give you peace of mind and body is great to incorporate into your night and morning routines. Habits such as reading, meditating, stretching, or journaling can help you stick to healthy sleep patterns while also engaging in active rest. Meditation is a powerful tool you can use that is proven to facilitate better sleep and improvements to heart health, blood pressure, and cognitive health

Using HRV To Develop Healthy Sleeping Patterns 

These are methods that help improve heart rate variability. These HRV readings give us helpful information to see when the body is experiencing a good balance of activation and rest, leading to better sleep and more energy. Using biofeedback devices can help us keep track of this critical metric and maintain a healthy, varied pace of life. Watch out for Hanu’s upcoming full sleep tracking and guidance features currently under development!

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