Resting heart rate (RHR) refers to the number of times your heart beats per minute when your body is at complete rest, such as when you are sitting calmly or lying down. For most adults, a typical RHR falls within the range of 60 to 100 beats per minute. A lower RHR often indicates greater cardiovascular fitness because it suggests your heart is working more efficiently to circulate blood throughout your body.
The Body’s Response: Why Resting Heart Rate Increases When Sick
When sick, your resting heart rate often increases as your body activates its immune system. The immune system releases signaling molecules, like cytokines, which increase metabolic demand.
The elevated metabolic rate requires more oxygen and nutrients to be delivered to tissues, prompting the heart to pump faster. Fever, a common symptom of illness, further contributes to this increase. For every degree Celsius (1.8 degrees Fahrenheit) rise in body temperature, your heart rate can increase by approximately 10 beats per minute. This heightened heart rate helps to dissipate heat and circulate immune cells more rapidly.
Inflammation, another hallmark of infection, also plays a role in raising RHR. Inflammatory processes can affect the autonomic nervous system, which regulates heart function, leading to a faster heart rate. This combined effort of increased metabolic activity, fever, and inflammation demonstrates the body’s adaptive strategy to overcome illness.
Other Influences on Resting Heart Rate During Illness
Beyond the direct immune response, other factors can elevate resting heart rate during illness. For example, dehydration, often from fever, vomiting, or diarrhea, reduces blood volume, making the heart work harder to maintain blood pressure and circulation. This leads to an increased heart rate.
Physical and mental stress associated with being unwell can also contribute to a higher RHR. The body releases stress hormones like adrenaline, which naturally accelerate heart rate. Certain over-the-counter medications, particularly decongestants found in cold and flu remedies, can contain ingredients like pseudoephedrine that stimulate the nervous system and elevate heart rate.
Pre-existing medical conditions, such as anemia, thyroid disorders, or underlying heart conditions, can further complicate the body’s response to illness and lead to greater increases in resting heart rate. These conditions can diminish the heart’s efficiency or alter its normal rhythm, making it more susceptible to fluctuations during illness.
Recognizing Concerning Resting Heart Rate Changes
While an elevated resting heart rate during illness is common, certain changes warrant medical attention. If your RHR consistently stays above 100 beats per minute, even after a fever has subsided, or if it represents a significant increase from your personal baseline, it could be a sign of a more serious issue. For instance, a persistent increase of 20-30 beats per minute above your typical RHR might be concerning.
Accompanying symptoms are also important indicators. Seek medical advice if an elevated heart rate is accompanied by shortness of breath, chest pain or discomfort, severe dizziness, or fainting spells. These symptoms, especially when combined with a high RHR, could indicate complications such as severe dehydration, an abnormal heart rhythm, or a more severe infection impacting organ function. This information should not replace professional medical advice; consult a doctor if you have concerns about your heart rate during illness.