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. The statement published in the Association's flagship journal Circulation outlines how factors such as rotating schedules, irregular sleep patterns, and light exposure at night can impair metabolic regulation, blood pressure control and hormonal balance. 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 help generate rhythmic activity that creates the body's internal clock.
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 increased risk of obesity and overweight. The timing and regularity of sleep also play a role in diabetes, with social jet lag and greater day-to-day variability in sleep duration emerging as risk factors for glycemic dysregulation and Type 2 diabetes. Light exposure timing serves as a therapeutic tool for circadian health. Morning exposure to natural light helps reinforce healthy rhythms, while exposure to 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 risk of cardiovascular disease.
Meal timing affects metabolic health beyond caloric content. Eating late at night or having irregular mealtimes can misalign the circadian clocks found in organs like the liver and pancreas, contributing to blood sugar spikes and weight gain. Studies show that eating earlier in the day, such as having breakfast before 8:00 a.m., is associated with lower risk of Type 2 diabetes and better cardiometabolic outcomes. Physical activity timing may enhance circadian health as exercise acts as a secondary synchronizer. Morning or afternoon workouts can help advance circadian rhythms, while evening exercise may delay them. The timing of physical activity may also influence outcomes like blood pressure, glucose control and sleep quality.
Circadian misalignment is particularly amplified by shift work, light pollution and inconsistent sleep patterns. Individuals working nontraditional schedules face increased exposure to light pollution, irregular mealtimes and inconsistent sleep compared to those with traditional day/night schedules. Misalignment from rotating and night shift work is an established cardiovascular disease risk factor. Individual internal clock timing, known as chronotype, should guide timing of interventions. A person's natural timing for sleep and activity affects how they respond to light, meals and exercise. Tailoring interventions to a person's chronotype 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 and artificial intelligence may soon make it easier to track individual body clock patterns.
Sleep is one of the key measures for improving and maintaining heart and brain health in the Association's Life's Essential 8. While more research is needed to establish causality and develop personalized interventions, optimizing circadian rhythms through consistent sleep schedules, regular meal times and appropriate light exposure offers a promising preventive strategy for cardiometabolic health.
