The American Heart Association released a new scientific statement today in its flagship journal Circulation, emphasizing that disruptions to the body's circadian rhythm—the internal 24-hour clock—are strongly linked to increased risk of cardiometabolic diseases, including obesity, type 2 diabetes, high blood pressure, and cardiovascular disease. The statement, titled "Role of Circadian Health in Cardiometabolic Health and Disease Risk," outlines how factors such as shift work, irregular sleep and meal times, and nighttime light exposure can misalign the body's internal clock, impairing metabolic regulation, blood pressure control, and hormonal balance.
According to the statement, circadian rhythms regulate key physiological processes like heart rate, blood pressure, metabolism, and hormone secretion. The central clock in the brain is synchronized primarily by light detected through the retina, while peripheral clocks in organs like the liver and pancreas respond to behavioral cues such as meal timing. Disruption occurs when a person's internal clock does not align with their behaviors—for example, when an evening person must wake early for work, forcing them to be awake during their biological night.
Key takeaways from the statement include the importance of sleep timing regularity, not just duration. Irregular sleep schedules, even with adequate sleep length, can disrupt circadian rhythms and have been linked to obesity and type 2 diabetes. "Social jet lag," or variations in sleep schedule between work and free days, is a risk factor for glycemic dysregulation. The statement also highlights light exposure as a therapeutic tool: morning natural light reinforces healthy rhythms, while artificial light at night, especially blue light from screens, can suppress melatonin and delay sleep onset, increasing cardiovascular disease risk.
Meal timing affects metabolic health beyond caloric content; eating late at night or at irregular times can misalign organ clocks, contributing to blood sugar spikes and weight gain. Studies cited in the statement show that eating breakfast before 8:00 a.m. is associated with lower type 2 diabetes risk. Physical activity timing may also enhance circadian health, with morning or afternoon workouts helping advance rhythms, though more research is needed to determine optimal timing for different individuals.
The statement notes that circadian misalignment is amplified by shift work, light pollution, and inconsistent sleep patterns, making shift workers particularly vulnerable. It also emphasizes that interventions should be tailored to an individual's chronotype—whether they are a "morning person" or "night owl"—to improve effectiveness. However, accurately measuring circadian rhythms remains challenging outside controlled lab settings. The writing group calls for more research to establish causality and develop personalized strategies using wearable devices and AI.
"Everyone has an internal clock, and it's time we start listening to it," said Kristen Knutson, Ph.D., FAHA, volunteer chair of the statement writing group and associate professor at Northwestern University. "Simple changes, like going to bed and waking up at the same time every day, eating meals earlier and getting morning sunlight, may make a meaningful difference in your heart and metabolic health." The statement is published in Circulation and can be viewed online at https://www.ahajournals.org/journal/circ. Additional resources include the AHA's Life's Essential 8 at https://www.heart.org/en/healthy-living/healthy-lifestyle/lifes-essential-8 and information on sleep health at https://www.heart.org/en/healthy-living/healthy-lifestyle/sleep.
