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Updated: Jan 30, 2026
Human Circadian Phenotyping and Diurnal Performance Testing in the Real World
Published on: April 7, 2020
Impact of mental stress, the circadian system and their interaction on human cardiovascular function
Frank A J L Scheer1, Sarah L Chellappa1, Kun Hu1
1Medical Chronobiology Program, Division of Sleep and Circadian Disorders, Brigham and Women's Hospital, Boston, MA, 02215, United States; Division of Sleep Medicine, Harvard Medical School, Boston, MA, 02215, United States.
Insights
Morning cardiovascular events are linked to circadian rhythms and mental stress. Combining mental stress with the natural morning circadian rhythm amplifies cardiovascular stress, increasing morning vulnerability.
Area of Science:
- Cardiovascular Physiology
- Chronobiology
- Stress Physiology
Background:
- Adverse cardiovascular events exhibit a morning peak, potentially influenced by circadian rhythms and stress.
- The interplay between the body's internal clock and acute stressors on cardiovascular function requires further investigation.
Purpose of the Study:
- To investigate the combined effects of mental stress and the endogenous circadian system on cardiovascular function.
- To determine if circadian timing modulates the cardiovascular response to mental stress.
Main Methods:
- 12 healthy adults participated in a 240-hour protocol with controlled behaviors and measurements.
- Mental stress was induced using serial addition tasks.
- Cardiovascular measures included hemodynamics, catecholamines, and heart rate variability for sympathovagal balance and cardiac vagal modulation.
Main Results:
- Mental stress elevated hemodynamic function, sympathovagal balance, and epinephrine levels, while decreasing cardiac vagal modulation.
- Circadian variations were observed in all measured cardiovascular parameters.
- The impact of mental stress on sympathovagal balance was greatest during the circadian morning, indicating a synergistic effect.
Conclusions:
- The endogenous circadian system and mental stress interact to influence cardiovascular function.
- The summation of circadian and stress-induced effects in the morning may explain heightened cardiovascular vulnerability during this period.
- Understanding these interactions is crucial for managing cardiovascular risk.
Abstract:
The risk for adverse cardiovascular events (e.g., myocardial infarction, sudden cardiac death) peaks in the morning, possibly due to the effects of the endogenous circadian system on cardiovascular risk factors, or the occurrence in the morning of specific triggers, such as mental stress. To assess any interacting effects on cardiovascular function of mental stress and the circadian system, 12 healthy adults underwent a 240-h protocol with all measurements and behaviors scheduled evenly across the circadian cycle. Mental stress was repeatedly induced by performance-motivated serial addition tasks. Cardiovascular measures included hemodynamic function (heart rate, blood pressure), circulating catecholamines (epinephrine, norepinephrine), and estimates of sympathovagal balance and cardiac vagal modulation derived from heart rate variability analyses. Mental stress increased hemodynamic function, sympathovagal balance and epinephrine, and decreased cardiac vagal modulation. Endogenous circadian variation occurred in all cardiovascular measures: sympathovagal balance peaked in the circadian morning (∼9 AM), cardiac vagal modulation in the circadian night (∼4 AM), and heart rate and circulating catecholamines in the late circadian morning/early afternoon (∼12 PM). Importantly, the effects of mental stress and the endogenous circadian system on cardiovascular function occurred in conjunction, such that mental stress in the circadian morning caused greatest sympathovagal balance. This summation of effects could contribute to the increased morning cardiovascular vulnerability.
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