When it comes to our sleep, various metrics of biological activity can provide insight into what the body is doing during sleep and whether it’s performing at the level it should. The key to finding value in their numbers, though, is to know what each metric is associated with and what abnormal levels may predict.
Heart rate variability (HRV) is one metric commonly used to ascertain the health of the heart and how adaptable it is to each situation in life. However, stress can cause HRV to lower, which can then have implications on your sleep.
This connection emphasizes the importance of lowering stress to improve your sleep and offers a metric that can provide insight into your stress level, cardiovascular fitness, and sleep quality.
What is Heart Rate Variability?
Heart rate variability (HRV) is the difference in timing between heartbeats. This variation is controlled by the autonomic nervous system (ANS), a part of the nervous system that regulates our heart rate, breathing, blood pressure, and digestion without us needing to think about it.
There are two subdivisions of the autonomic nervous system: the parasympathetic and sympathetic nervous systems. The former is your relaxation response, and the latter is your fight-or-flight response.
Our brain continually processes what goes on around us to determine which of these two subdivisions should be more prominent, and they each have their time to shine. However, while some stress and fight-or-flight responses are normal, if they shift into overdrive, problems can occur. The challenge, though, is knowing when the body is acting more stressed than it should, especially if you don’t feel stressed.
This is where HRV can step in, serving as a possible way to identify imbalances in the autonomic nervous system. Generally, your HRV is lower when you’re in more of a fight-or-flight mode, whereas the more relaxed you are, the greater the variation between heartbeats. As such, the higher your HRV, the less stressed you tend to be.
A higher HRV is a sign that your body is more adaptive to whatever life throws at it. In comparison, a low HRV can indicate current or future health problems because it shows that your body is less capable of handling changing situations.
As explained in one HRV overview, the heart should not be as steady as a metronome. Instead, it should have variances in its beats as it adapts to stimuli.
Heart Rate Variability During Sleep
Generally, HRV is shown to be higher during sleep, which supports the idea that sleep is a time when vagal activity is dominant and sympathetic activity (your fight-or-flight response) is relatively inactive. This is considered true no matter which stage of sleep you’re in, whether non-rapid eye movement (NREM) or REM.
As for how your HRV varies during the night, it’s based on which sleep stage you’re in. The NREM stages are when the vagal influence on heart rate is the greatest, and as you transition to REM sleep, this vagal influence declines, leading to a lower HRV.
Some sleep disorders may cause a higher HRV during sleep, such as sleep apnea. This disorder is characterized by episodes of stopped breathing, and research has shown that the high HRV is accompanied by sympathetic dominance, which is also characteristic of stress.
Additionally, cardiac conditions can affect HRV during sleep. For example, myocardial infarction results in a complete loss of vagal activation, producing low HRV during both NREM and REM sleep stages.
The Impact of Stress on HRV
Stress can negatively affect many areas of your health, including your HRV.
One review on stress’s influence over HRV reported that, during stressful situations, your body sends signals to the heart that increase your heart rate. However, this consistently high heart rate causes HRV to lower.
Generally, you want your HRV to be high because it means that it changes more easily as your sympathetic and parasympathetic nervous systems send their individual signals. However, when you’re stressed, your sympathetic nervous system becomes dominant, which causes your HRV to lower and makes your heart less capable of adapting.
This connection between stress and HRV may explain how stress disrupts sleep.
Research has found that acute psychophysiological stress is associated with decreased levels of parasympathetic modulation while in the NREM and REM stages of sleep and increased sympathetic activity during NREM sleep, which generally correlates to a lower HRV. These higher levels of sympathetic activity during NREM sleep were associated with lower delta activity, which are brain waves that occur during deep sleep. Essentially, this research shows that stress lessens the amount of deep sleep you may get, leading to poorer quality sleep.
How to Improve Your HRV
If you’re interested in improving your HRV and helping your body become more resilient to life’s challenges, you can:
- Exercise regularly. This helps to improve your heart’s health along with the health of your entire body—it may even prevent health diseases that can cause a low HRV.
- Follow a healthy, balanced diet. For an extra boost to your heart, focus on heart-healthy foods such as vegetables, fruits, healthy fats, and foods high in fiber.
- Reduce stress. As we’ve seen, stress can cause your HRV to rise, so reducing your stress levels can go a long way in improving your heart’s health.
Chill Out! Tips For Reducing Stress
As mentioned, one way to improve your HRV and ensure your heart remains adaptive is to reduce your stress levels, but this is often easier said than done.
Chronic stress can feel like a constant part of our lives, but these activities can help you break from stress once and for all:
- Deep breathing
- Progressive muscle relaxation
- Mindfulness
- Yoga
- Meditation
- Listening to soothing music
- Crafting
- Cutting back on caffeine
- Spending time with friends and family
- Laughing
- Aromatherapy
Optimizing HRV and Reducing Stress to Sleep Better
If you’re looking for the culprit of your poor sleep, look no further than stress, which is a common part of most of our lives. Stress is known to lower HRV due to the overactivation of the sympathetic nervous system, and these same effects can be seen while you’re sleeping, too. However, this increased activity of the sympathetic nervous system not only lowers HRV but also lessens the amount of deep sleep you get.
If you’re looking to monitor your sleep through various metrics, HRV can be a valuable one since it can indicate when your sympathetic nervous system is taking over, which can lead to sleep problems. HRV can be used to gauge how well you’re sleeping, and it has even been used as a screening tool for sleep disorders.
Ultimately, to support your heart’s health, your goal should be to increase your HRV. Since stress is one thing that affects your HRV, by lowering your stress, not only will you feel better mentally, but you’ll be able to sleep better, which brings along a host of health benefits.
