The American Heart Association has issued a scientific statement revealing that 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. Published in the Association's flagship journal Circulation, the statement details how factors like rotating schedules, irregular sleep patterns, and nighttime light exposure 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 synchronizes primarily through light detected by the retina and transmitted to neurons in the brain's hypothalamus region, where special genes and proteins generate rhythmic activity that creates the body's internal clock. Sleep timing regularity proves as important as sleep duration for maintaining circadian health, with irregular schedules disrupting rhythms even with adequate sleep length.
Social jet lag, or variations in sleep schedule between work days and free days, links to increased obesity risk, while greater day-to-day variability in sleep duration emerges as a risk factor for glycemic dysregulation and Type 2 diabetes. Light exposure timing serves as a therapeutic tool, with morning natural light reinforcing healthy rhythms and nighttime artificial light, especially blue light from screens, suppressing melatonin and delaying sleep onset. Even low nighttime light levels associate with increased cardiovascular disease risk.
Meal timing 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. Studies show eating earlier in the day, such as breakfast before 8:00 a.m., associates with lower Type 2 diabetes risk and better cardiometabolic outcomes. Physical activity timing may enhance circadian health as exercise acts as a secondary synchronizer, with morning or afternoon workouts potentially advancing rhythms while evening exercise may delay them.
Circadian misalignment amplifies particularly through 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 traditional schedules, with misalignment from rotating and night shift work established as a cardiovascular disease risk factor. Individual internal clock timing, known as chronotype, should guide intervention timing, as a person's natural sleep and activity timing affects responses to light, meals and exercise.
Tailoring interventions to chronotype may improve effectiveness and support circadian alignment. While researchers currently measure circadian rhythms accurately only in controlled lab settings, new technologies like wearable devices and artificial intelligence may soon facilitate tracking individual body clock patterns. Sleep represents one key measure for improving heart and brain health in the Association's Life's Essential 8. Though more research needs 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.
