In today’s digital age, we tend to geek out over numbers, stats, graphs and smartwatches that measure all kinds of values related to our health. When it comes to your heart rate, those numbers often indicate how hard your heart is working to keep you healthy and alive. But what do those numbers mean exactly — and how do they change when you’re active versus at rest or asleep?
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Well, for starters, your heart rate is determined by how many heartbeats you have per minute. And that number can go up or down based on any activities you’re doing (or not doing) and several systems that play off each other. Your autonomic nervous system (what allows you to do things like breathing or have a heartbeat without thinking about it) largely controls your resting heart rate.
The autonomic nervous system has two components: the sympathetic nervous system (fight-or-flight) and the parasympathetic nervous system (calm-and-relaxed). It’s the balance between these two opposing systems that has a big impact on your heart rate.
“You can think of your heart rate as a reflection of what’s going on in your body and mind at that moment,” says cardiologist Michael Faulx, MD. “When your heart rate runs faster than average, it’s often a reflection of the predominance of the sympathetic nervous system. In essence, you are in a relative state of stress for some reason.”
In most cases, your resting heart rate is an indicator of your overall health, and adults want it to be between 60 and 100 beats per minute (bpm). But what does your sleeping heart rate say about you, particularly when those numbers are often far below the 60-beats-per-minute threshold or above 100 beats per minute when you’re dreaming?
Dr. Faulx explains how your heart rate changes when you sleep, and whether those numbers should be a cause for concern.
Your resting heart rate is lower than your active heart rate. Similarly, your sleeping heart rate normally falls lower than your waking heart rate because your heart basically switches on its autopilot.
“Generally speaking, your sleeping heart rate runs about 20% to 30% lower than your daytime resting heart rate,” says Dr. Faulx.
And your heart rate ebbs and flows based on the stages of sleep you cycle through.
“During non-REM sleep is when your heart rate and blood pressure tend to cycle down, particularly during deep sleep,” explains Dr. Faulx. “You can think of it as a period where your heart gets to hibernate during the night and rest, so it doesn’t have a fast heart rate.”
“On average, a healthy adult will run a heart rate of about 60 to 100 beats per minute during the day, and their normal heart rate during sleep would be like 50 to 75 beats per minute,” says Dr. Faulx.
But children are very different because adult heart rates tend to slow as we get older.
“With children, resting heart rates are faster and it really depends on their age,” he explains. “A child’s heart rate is often more than 100 beats per minute and that’s considered normal. Babies and toddlers can even have heart rates north of 130 and that’s also considered normal.”
With so much variability at play, what’s considered an abnormal sleeping heart rate? If you were to base the answer to this question solely on the numbers, any sleeping heart rate outside of the range of 40 to 100 beats per minute would be considered abnormal — but fixating on just the numbers can complicate matters.
“What’s normal for an individual can vary based on a number of factors like your age, weight, genetics, physical activity and other health conditions you have,” clarifies Dr. Faulx. “If you’re having a sleeping heart rate of below 40 beats per minute or above 100 beats per minute during sleep as an adult, that would be outside of the normal range. Whether that’s something to be concerned about or not really depends on how you feel and what other medical conditions there are.”
“As you progress through pregnancy, your total blood content and your total output from your heart increases by at least 50% by the time you hit the third trimester,” shares Dr. Faulx. “We expect heart rates to go up during pregnancy. So, if you have a sleeping heart rate that’s a little above 100 beats per minute and you’re pregnant but otherwise feel well, that’s nothing to be alarmed by. That’s just the physiology of pregnancy.”
“If you have a lot of anxiety, you’re going to have more of these stress hormones floating around in your bloodstream that are going to result in a higher blood pressure and a faster sleeping heart rate,” says Dr. Faulx. “Addressing your anxiety would then result in lower heart rate, lower blood pressure and generally better health.”
We know that when you’re exercising, your heart beats faster to keep up with the demand of your sympathetic nervous system and the autonomic need to keep you breathing and your blood pumping throughout your body. But when you’re resting or asleep, your parasympathetic nervous system has the ability to relax you far more easily on the other side because your vagus nerve has been strengthened.
“The vagus nerve is a nerve that begins in the brainstem and has connections to your entire body, specifically your heart, lungs and gut,” says Dr. Faulx. “People who have more aerobic fitness will have slower heart rates because of the effect of the vagus nerve.”
When your vagus nerve is active, it lowers your blood pressure and slows your heart rate, so every time you push yourself and you get your heart rate up, you’re training that vagus nerve to kick in and slow it down.
“For example, well-trained athletes like endurance athletes, marathon runners, triathletes — their vagal nerve tone is so high that when they sleep, they might get heart rates in the 30s or even lower,” he continues. “As long as they’re feeling well and they’re not having symptoms during the day, we don’t really get alarmed by that.”
Remember that when you sleep, it’s a time for your heart to rest, relax and recover. But that means if you never reach that deep-sleep state, your sleeping heart rate will likely not hit the lower end of the spectrum and it will tend to run higher than you expect.
“With sleep apnea — when your breathing is cut off multiple times during the night — your mind and body are in a state of constant distress and you don’t cycle normally through the stages of sleep,” notes Dr. Faulx. “As a result, there is no period during sleep where you’re in a state of recovery. Your blood pressure is higher, your heart rate is higher and those can even extend into the next day.”
Other conditions and sleep disorders that affect your sleeping heart rate include:
Water has its many health benefits, including keeping you alive.
“If you’re dehydrated, your heart doesn’t have a chance to fill normally and get prepared for each normal beat because the filling pressures are low,” says Dr. Faulx. “People who are dehydrated typically have faster resting heart rates and faster sleeping heart rates.”
Medications like beta-blockers to treat high blood pressure can cause your sleeping heart rate to run slower. Other stimulant medications for ADHD and psychiatric medications like antidepressants can also have an impact on your blood pressure and heart rate while sleeping.
And a variety of conditions like the following can also impact your sleeping heart rate:
“If the wiring in your heart isn’t working properly or if your thyroid is underactive or overactive, it can result in a lower or higher sleeping heart rate depending on what you’re dealing with,” adds Dr. Faulx.
“One reason people might want to track their sleeping heart rate would be if they feel unwell in some way,” notes Dr. Faulx.
If you experience any of these symptoms, you should make an appointment with a healthcare provider to get evaluated:
“If you have any symptom that you don’t feel comfortable with, these are all things in the context of sleeping heart rates that are outside of the normal range that I encourage people to get checked out,” advises Dr. Faulx.
“If your heart rate is substantially above 100 beats per minute during sleep, it might also warrant some investigation, even if you feel OK because it might reflect something going on like a sleep disorder. And if you’re documenting heart rates in the 20s, that might warrant a conversation with your doctor just to verify that’s accurate.”
Overall, exercise, weight management and good sleep hygiene can all have a positive impact on your sleeping heart rate.
In general, Dr. Faulx recommends moderate-intensity aerobic exercise 30 minutes a day, five days a week. While exercising, you’ll want to try spend as much time as you can within your target heart rate to help lower your blood pressure and lower your heart rate over time. Not sure what your target rate is? Follow this simple formula:
“To calculate your maximum predicted heart rate, take 220 minus your age,” explains Dr. Faulx. “For cardiac fitness, your target heart rate should be 65% to 75% of that maximum when you’re exercising.”
By improving on these areas and by treating other underlying conditions that may have an effect on your sleeping heart rate, you can make vast improvements on your overall health — and the numbers associated with wellness.