Circadian Rhythm Disruptions Linked to Increased Cardiometabolic Disease Risk

Disruptions to circadian rhythms, the body's internal 24-hour clock, are strongly associated with increased risk of obesity, Type 2 diabetes, high blood pressure and cardiovascular disease according to a new scientific statement from the American Heart Association published in its flagship journal Circulation. The statement outlines how factors such as rotating schedules, irregular sleep patterns, light exposure at night and inconsistent meal times can impair metabolic regulation, blood pressure control and hormonal balance, contributing to disease progression.

Circadian rhythms regulate key physiological processes including heart rate, blood pressure, metabolism and hormone secretion. The circadian system is synchronized primarily through light detected by the retina and transmitted to special neurons in the brain's hypothalamus region. Inside these neurons and throughout the body, special genes and proteins like CLOCK, BMAL1, PER and CRY generate rhythmic activity that creates the body's internal clock timing.

Sleep timing regularity is as important as sleep duration for maintaining circadian health. Irregular sleep schedules, even with adequate sleep length, can disrupt circadian rhythms. Social jet lag, or variations in sleep schedule between work days and free days, has been linked to obesity risk and emerges as a risk factor for glycemic dysregulation and Type 2 diabetes. Maintaining consistent sleep and wake times helps synchronize the body's internal clock and supports metabolic health, with sleep being one of the key measures in the Association's Life's Essential 8 for improving heart and brain health.

Light exposure timing serves as a therapeutic tool, with morning exposure to natural light reinforcing healthy rhythms while artificial light at night, especially blue light from screens, can suppress melatonin and delay sleep onset. Even low levels of nighttime light have been associated with increased cardiovascular disease risk. Meal timing also affects metabolic health beyond caloric content, as eating late at night or having irregular mealtimes can misalign circadian clocks in organs like the liver and pancreas, contributing to blood sugar spikes and weight gain.

Physical activity timing may enhance circadian health, with morning or afternoon workouts potentially helping advance circadian rhythms while evening exercise may delay them. The timing of physical activity may influence outcomes like blood pressure, glucose control and sleep quality, though more research is needed to determine optimal timing for different individuals. Circadian misalignment is amplified by shift work, light pollution and inconsistent sleep patterns, with misalignment from rotating and night shift work established as a cardiovascular disease risk factor.

Individual internal clock timing, known as chronotype, should guide timing of interventions since morning people and night owls respond differently to light, meals and exercise. Tailoring interventions to a person's natural timing may improve effectiveness and support circadian alignment. Currently, researchers can only measure circadian rhythms accurately in controlled lab settings, but new technologies like wearable devices, advanced lab tests and artificial intelligence may soon help track patterns in skin temperature and heart rate over 24 hours to provide clearer pictures of individual body clock rhythms.

This scientific statement was prepared by the volunteer writing group on behalf of the American Heart Association Council on Lifestyle and Cardiometabolic Health and other councils. American Heart Association scientific statements promote greater awareness about cardiovascular diseases and stroke issues and help facilitate informed health care decisions. The statement emphasizes that optimizing circadian rhythms offers a promising preventive strategy for cardiometabolic health, with behavioral interventions to better regulate the body's schedule potentially improving circadian alignment and reducing cardiometabolic risk.