The American Heart Association warns that disrupted circadian rhythms, from irregular sleep, late-night meals, or shift work, can raise the risk of obesity, diabetes, and heart disease, while consistent daily patterns may offer a new path to better cardiometabolic health.
Role of Circadian Health in Cardiometabolic Health and Disease Risk: A Scientific Statement From the American Heart Association. Credit: Billion Photos / Shutterstock
In a recent scientific statement in the journal Circulation, experts from the American Heart Association (AHA) reviewed the evidence regarding the impact of the circadian system on metabolic and cardiovascular health.
They emphasized that promoting circadian alignment through regular sleep, exposure to morning light, and appropriately timed exercise and meals may improve cardiometabolic health and is associated with lower cardiovascular risk, although causal evidence remains limited, and establishing such links is a research priority. The authors further clarify that circadian health is a broader concept than sleep health, encompassing the 24-hour regulation of physiological processes beyond sleep itself.
Circadian Disruption Linked to Disease
Human physiology follows approximately 24-hour cycles governed by the circadian system, which coordinates key functions such as hormone secretion, metabolism, cardiac performance, and vascular tone.
These internal rhythms are maintained by a central clock in the hypothalamus and peripheral clocks in tissues. They help synchronize bodily functions with the external light-dark cycle. Endogenous circadian rhythms differ from diurnal patterns driven by external cues, such as light or behavior, and this distinction is important for understanding physiology. Disrupted synchronization can harm cardiometabolic health and raise risks for obesity, diabetes, and cardiovascular disease.
Recognizing the growing evidence linking circadian disruption to disease, the AHA developed this scientific statement to summarize current understanding of circadian biology in relation to cardiovascular and metabolic outcomes.
The circadian system regulates daily physiological rhythms, and several key factors affect its synchronization.
Light Exposure as the Strongest Circadian Cue
Light exposure is the strongest environmental cue. Morning sunlight or bright indoor light aligns the body’s internal clock with the external day-night cycle, promoting alertness and better sleep quality. In contrast, bright light in the evening, particularly from blue-light-emitting devices, delays circadian timing, suppresses melatonin, and interferes with sleep onset.
Effects of Sleep, Wake Patterns on Circadian Timing
Sleep and wake patterns both influence and can modify the circadian system. Going to bed or waking earlier advances the circadian phase, while later sleep schedules delay it. Irregular sleep timing, such as that seen in shift work or jet lag, disrupts exposure to natural light cues, leading to misalignment.
Role of Meal Timing in Metabolic Synchronization
Meal timing acts as a secondary cue. It mostly affects peripheral clocks in organs like the liver and pancreas. Eating late at night or across long time windows can desynchronize metabolic rhythms and raise risks for obesity, type 2 diabetes, and cardiovascular disease.
Early eating patterns, aligned with daytime activity, are linked to improved metabolic outcomes.
Exercise Timing and Circadian Adaptation
Exercise also exerts time-dependent effects on circadian rhythms. Morning or afternoon exercise can advance the internal clock, while evening exercise may delay it. Although its effects are weaker than those of light exposure, physical activity helps synchronize peripheral tissues, especially in skeletal muscle, which plays a crucial role in glucose and lipid metabolism. However, optimal exercise timing remains uncertain and may vary by chronotype, medication use, and feeding state. Individualized approaches that consider these factors may help optimize cardiometabolic outcomes.
Circadian Misalignment and Cardiometabolic Disorders
Misalignment between internal circadian rhythms and external behaviors contributes to several metabolic and cardiovascular disorders. For example, obesity has been closely tied to irregular sleep and eating schedules.
Shift workers and individuals with high variability in sleep timing or duration exhibit higher body mass index and greater central adiposity. Eating during the biological night further promotes weight gain by altering appetite hormones, lowering energy expenditure, and disturbing glucose metabolism.
Circadian Disruption and Type 2 Diabetes Risk
In type 2 diabetes, disrupted daily rhythms in activity, sleep, and meals impair insulin sensitivity and glucose control. Individuals with irregular schedules, especially shift workers, display higher fasting glucose, glycated hemoglobin, and incidence of diabetes. Late-night eating and reduced fasting durations exacerbate glycemic dysregulation, while early time-restricted eating improves glucose tolerance. Evidence for glycemic benefits of strict 8-hour daytime eating windows is mixed; however, time-restricted eating has been associated with improvements in weight, adiposity, and lipid levels.
Blood Pressure Rhythms and Hypertension Risk
Circadian rhythm irregularities are also linked to hypertension, as normal blood pressure follows a daily dipping pattern during sleep. Nighttime light exposure, irregular meals, and shift work blunt this rhythm, raising blood pressure and cardiovascular risk. Additionally, the risk of cardiovascular disease rises with circadian disruption: shift workers experience a 17% higher risk, and inconsistent sleep schedules more than double disease incidence. Later meal timing and nighttime light exposure have also been associated with higher stroke and heart disease risks. Large clinical trials have not found consistent benefits of bedtime versus morning antihypertensive dosing on major outcomes, suggesting timing should prioritize adherence, except possibly in nondippers or shift workers. The AHA highlights that these results underscore the importance of personalized clinical recommendations rather than uniform chronotherapy approaches.
Strategies to Improve Circadian and Metabolic Health
Improving circadian alignment offers an opportunity to reduce the burden of cardiometabolic disease. Behavioral interventions that promote consistent sleep-wake cycles and early, regular mealtimes can stabilize internal rhythms. Reducing variability in bedtime has been linked to improved weight and body composition. Melatonin supplementation, though effective at adjusting sleep timing, requires caution due to inconsistent dosing and uncertain metabolic effects.
Light Therapy and Morning Light Exposure
Light therapy has demonstrated benefits for mood, alertness, and body composition, with morning light exposure associated with lower body fat and body mass. According to the AHA, such interventions may be particularly beneficial for individuals exposed to limited daylight, including shift workers and those living at high latitudes.
Time-Restricted Eating for Metabolic Optimization
Time-restricted eating, typically an eight-hour daytime eating window, aligns nutrient intake with circadian activity and may support metabolic health by improving insulin sensitivity, weight, and lipid measures. Nonetheless, further trials are needed to confirm whether these effects are consistent across populations and metabolic states.
Exercise Timing for Personalized Circadian Benefits
Timed exercise helps regulate peripheral clocks and enhance sleep quality, although its optimal timing remains to be defined and may depend on individual chronotype. Morning activity may aid weight control, while afternoon or evening sessions may better support glucose regulation. Further controlled studies are needed to determine the most effective timing of exercise interventions for different populations. Exercise-timing research should also account for chronotype, medication use, and habitual meal patterns to better inform clinical recommendations.
Emerging Field of Circadian Medicine
Current evidence on effective interventions underscores the growing potential of “circadian medicine,” a behavioral and clinical framework integrating the timing of sleep, meals, light, and exercise, to improve metabolic and cardiovascular outcomes.
Future research should focus on establishing causal links, developing accurate and scalable methods to measure circadian rhythms, and testing practical interventions that optimize light exposure, sleep, and meal timing to improve overall cardiometabolic health. Tailoring such strategies to chronotype and reducing environmental inequities, such as light pollution and shift-work burden, are also key to advancing equitable circadian health. Developing accessible biomarkers and wearable technologies to objectively assess circadian phase is highlighted as a crucial next step in translating circadian science into clinical and public-health practice.
Journal reference:
- Knutson, K. L., Dixon, D. D., Grandner, M. A., Jackson, C. L., Kline, C. E., Maher, L., Makarem, N., Martino, T. A., St-Onge, M.-P., Johnson, D. A. (2025). Role of Circadian Health in Cardiometabolic Health and Disease Risk: A Scientific Statement From the American Heart Association. Circulation. DOI: 10.1161/CIR.0000000000001388, https://www.ahajournals.org/doi/10.1161/CIR.0000000000001388