Michelle L. Gumz, PhD, FAHA, Co-Director of the Center for Integrative Cardiovascular and Metabolic Disease (CICMD), served as Vice Chair of the writing group for a new American Heart Association Scientific Statement examining the importance of time of day as a biological variable in cardiometabolic and kidney research. Learn More
Circadian rhythms—the body’s approximately 24-hour biological cycles—affect processes throughout the cardiovascular, metabolic, and renal systems. Molecular pathways, gene expression, blood pressure, kidney function, metabolism, physical activity, sleep, and other physiological processes can vary substantially throughout the day and night.
The statement also highlights an important challenge in translating laboratory discoveries into human health. Humans are generally active and consume most of their food during the daytime, while mice and rats—the most commonly used animals in preclinical biomedical research—are nocturnal. Many laboratory experiments are therefore conducted during the animals’ normal rest period, while clinical research in humans generally occurs during their active period. This mismatch has the potential to influence experimental findings and their translation to human disease.
The authors encourage researchers to incorporate time of day into experimental design and reporting. Recommended practices include consistently documenting when samples and measurements are collected, selecting biologically appropriate times for experiments, and accounting for factors such as light exposure, meal timing, activity, and sleep.
These considerations are particularly relevant to cardiovascular and kidney research. Blood pressure normally changes throughout the day and falls during sleep, while kidney functions such as glomerular filtration and fluid and electrolyte excretion also follow strong circadian rhythms.
Looking ahead, the authors identify circadian biology as a promising avenue for precision health. Wearable technologies and continuous monitoring of measures such as blood pressure, heart rate, glucose, temperature, activity, and sleep may provide new opportunities to understand how biological timing influences disease and ultimately inform more personalized approaches to prevention and treatment.
The statement was authored by David M. Pollock, PhD, FAHA (Chair); Tami A. Martino, PhD; Kristen L. Knutson, PhD, FAHA; Satchidananda Panda, PhD; Amandine Chaix, PhD; Ketema Paul, PhD; Daichi Shimbo, MD, FAHA; and Michelle L. Gumz, PhD, FAHA (Vice Chair) on behalf of the American Heart Association Kidney in Heart Disease Science Committee of the Council on the Kidney in Cardiovascular Disease; Council on Cardiovascular and Stroke Nursing; and Council on Lifestyle and Cardiometabolic Health.
The statement reinforces an important message for the research community: time of day is a biological variable, and accounting for it can strengthen scientific rigor, improve reproducibility, and enhance the translation of research discoveries into better patient care.