A person’s heart rate while sleeping, often referred to as Sleep HR, differs from the standard resting heart rate (RHR) taken while awake. The RHR is typically measured when a person is calm but still conscious, and factors like mild anxiety or recent activity can subtly elevate it. Sleep HR, by contrast, represents the lowest heart rate the body reaches during a 24-hour cycle. It offers insights into health that daytime measurements cannot fully capture.
The Typical Heart Rate Range During Sleep
For most healthy adults, a normal sleeping heart rate generally falls within the range of 40 to 60 beats per minute (bpm), which is significantly lower than the typical awake RHR of 60 to 100 bpm. The heart rate drop during sleep is expected.
It is most common for the heart rate to reach its lowest point during the deepest stages of non-Rapid Eye Movement (non-REM) sleep. This range represents a broad average, and the ideal number can vary considerably from one person to the next. A heart rate consistently below 40 bpm is generally considered too low, but for a highly conditioned athlete, this rate may reflect superior cardiovascular efficiency.
The Body’s Mechanism for Slowing the Heart
The physiological process that orchestrates the heart rate decrease during sleep is primarily governed by the autonomic nervous system (ANS). The ANS operates through two opposing branches: the sympathetic nervous system, known as the “fight-or-flight” response, and the parasympathetic nervous system, commonly called “rest and digest”. As a person falls asleep, the influence of the sympathetic system diminishes, and the parasympathetic system takes over, promoting relaxation and energy conservation.
This shift in dominance causes a reduction in the body’s metabolic demands. With the muscles relaxed and brain activity slowing, the heart does not need to pump blood as forcefully or as quickly to supply oxygen. The deepest heart rate reduction occurs during the non-REM stages of sleep, the period when the body focuses most intensely on physical repair and recovery.
Recent research suggests that the heart’s natural pacemaker, the sinus node, possesses its own intrinsic biological clock, independent of the ANS. This internal circadian rhythm allows the sinus node to anticipate the night and proactively slow the heart rate. This mechanism involves a protein called the “funny channel” (HCN4), which controls the heart rate and is regulated by a clock gene.
Personal Factors Affecting Your Sleep Heart Rate
While the body’s mechanisms promote a lower heart rate during sleep, many personal variables contribute to an individual’s specific range. A person’s fitness level is a major factor, as highly trained endurance athletes often have a significantly lower Sleep HR due to a more efficient heart that pumps more blood per beat. For some athletes, a rate in the low 40s or even upper 30s can be entirely normal.
Age plays a role, as average sleeping heart rates tend to be slightly higher in older adults. Certain medications, such as beta-blockers, are designed to slow the heart and will artificially lower both the RHR and the Sleep HR. Lifestyle choices close to bedtime can elevate the nightly rate, including consuming alcohol, nicotine, or caffeine, all of which act as stimulants.
Sleep disorders can dramatically affect the nightly pattern, most notably obstructive sleep apnea. During apnea events, breathing stops and oxygen levels drop, which triggers a stress response that forces the heart to work harder. This constant stress and disruption to the normal sleep cycle prevent the heart rate from achieving its naturally low, restorative state.
When a Sleeping Heart Rate Signals a Problem
A sleeping heart rate that consistently falls outside the healthy physiological range may be a signal of an underlying health issue. An adult heart rate that drops below 40 bpm, a condition known as bradycardia, should be monitored, especially if it is accompanied by symptoms like dizziness, fatigue, or shortness of breath. For individuals who are not highly conditioned athletes, such a low rate could indicate a severe sleep disorder, hypothyroidism, or a primary cardiac issue.
Conversely, a consistently high heart rate during sleep, known as nocturnal tachycardia, is also a concern. A Sleep HR persistently above 90 or 100 bpm suggests the body is in a state of stress and is not achieving proper recovery. This can be caused by chronic anxiety, infection, high blood pressure, or undiagnosed sleep apnea, which keeps the sympathetic nervous system abnormally active.
If a person notices a sudden, persistent change in their average Sleep HR, consulting a healthcare provider is recommended. Seeking medical advice is particularly important if the unusual readings are paired with physical symptoms like chest pain or palpitations, as monitoring these trends can provide a physician with valuable data to diagnose and address any potential cardiovascular or sleep-related conditions.