Copyright TODAY
Timing is everything. As daylight saving time approaches, the American Heart Association reminds us that regular interruptions to our body’s internal clock don’t just cause inconvenient sleep disturbances but may also trigger adverse effects, especially with our hearts. “We need to develop methods to determine a person’s internal clock timing and synchronization so that we can personalize recommendations for the timing of sleep, meals, exercise, medications and therapy,” Kristen Knutson, Ph.D., volunteer chair of the American Heart Association Scientific Statement writing group, tells TODAY.com. The statement, about the role circadian rhythm plays in heart health, published on Oct. 28, 2025, represents the consensus of leading experts in heart disease and stroke. “To my knowledge, this is the first scientific statement to directly address the body’s 24-hour circadian rhythm and to link it with other recommendations, such as physical activity, sleep and dietary intake,” Collin Jeffrey Popp, Ph.D., assistant professor, Department of Population Health at NYU Langone Health, who is also a registered dietitian, tells TODAY.com. He was not part of the statement committee. What Is Circadian Rhythm? Circadian rhythm is the body’s internal clock that cycles approximately every 24 hours. The clock is synchronized with light. After our eyes detect light, they transmit messages to a special part in the brain, which contains genes that control the body’s 24-hour cycle, according to the Cleveland Clinic. Our circadian rhythm gets disrupted when our internal clock is not synchronized with our behaviors. For example, an “evening person” may not feel well if they must get up for an early international flight when they are normally asleep (called their biological night), according to the statement. “I think it’s essential for the public to realize that misalignment of our internal body clock to that of the external environment can increase the risk for certain diseases, like high blood pressure, diabetes and obesity,” Popp says. “Often, people come to see me wanting to lose weight, but they are doing all the right things -- eating healthy and working out, yet their weight does not budge.” How Does Circadian Rhythm Affect Our Heart Health? “Poor sleep patterns, such as inadequate amounts of sleep, are increasingly recognized as a risk for cardiovascular diseases,” Dr. Deepak L. Bhatt, director of Mount Sinai Fuster Heart Hospital at the Dr. Valentin Fuster professor of cardiovascular medicine at Icahn School of Medicine at Mount Sinai in New York, tells TODAY.com. He was not part of the committee on the scientific statement. Our circadian clock helps to regulate many aspects of heart function, such as blood pressure and heart rate — so when our circadian system is disrupted, it can impair these vital functions, Knutson adds. For example, normal blood pressure decreases at night when our body is in a restful state, according to past research. But when it doesn’t dip as low as it normally would at night during sleep, this is associated with increased risk of developing heart disease, she says. But there is no one-size-fits-all type of schedule when it comes to eating, sleeping or exercising. “I cannot make such a schedule, and I wish I could,” Knutson says. “The reason why I can’t is because it depends on a person’s internal clock timing, so 7 a.m. on the clock on the wall isn’t 7 a.m. for everyone’s internal clock.” But here are some general recommendations from experts. When Is a Good Time To Eat Breakfast and Dinner? Eating breakfast shortly after you wake up is a good idea unless you have been woken earlier than your internal clock wants you to wake up, like someone who wakes up early for work or a teenager going to school, Knutson says. A 2023 study found that consistently eating breakfast before 8:00 a.m. is associated with a lower risk of Type 2 diabetes compared to later breakfast times. It’s also important not to eat right before going to bed. “Having dinner 3-4 hours before you plan to go to bed is a good strategy to avoid eating too late in the day,” Knutson adds. Eating an earlier dinner better aligns with the body's circadian rhythm. This is beneficial to metabolic outcomes and wellbeing, TODAY.com previously reported. A 2022 study found that those who eat dinner later burn calories more slowly and store more fat. Eating late was also associated with feeling hungier and less satisfied after a meal. What Is a Good Schedule To Go to Bed? One of the first questions Popp poses to his patients is: “What’s your sleep/wake cycle like?” Sleeping fewer than six hours and eating late at night (even health foods) can blunt weight-loss efforts and harm your overall health, he says. Most people should aim for eight hours in bed during their “biological night,” Knutson adds. For most adults, who are not shift workers or jet lagged, this will mean going to bed between 10 p.m. and midnight. If someone has an early internal clock (such as a "morning person" who tends to wake up early), then they should go to bed earlier versus someone who has a late clock (such as is a "night owl"), then they should go to bed later at night. Past research, however, suggests those who sleep later at night are at higher risk for health problems, including Type 2 diabetes, obesity, hypertension and heart disease — regardless of sleep duration. “As a researcher and dietitian, one recommendation I give to folks, regardless of their health goal, is to avoid eating late, and if you need to eat late, make it a small meal,” Popp adds. Dinnertime is when the body begins to wind down, TODAY.com previously reported, so your calories should do the same. When Is a Good Time To Exercise? “The best time to exercise within the daytime remains to be determined and also will vary by a person’s internal clock,” Knutson says. “However, it is best to exercise during your biological daytime and not during the night.” How To Prevent Circadian Rhythm Disruption? Experts recommend focusing on sleep timing and light exposure. People should go to bed at the same time and wake up at the same time every day — including weekends, Bhatt says. Variations in sleep schedule, such as sleeping in on the weekends or having different sleep schedules on work or school days, are associated with a higher risk of being overweight or obese in both adults and adolescents, according to a 2023 study. People often discount how light exposure during the day helps to synchronize our circadian rhythms. Early morning light can support your health and sleep cycle by helping the body’s internal clock sync with the outside world, Popp says. The natural light helps reinforce our internal clock, but electronic devices can trick our minds into thinking we should be awake when we are trying to go to bed. “Exposure to artificial light from handheld devices at night or late snacking also contributes to disturbing the natural circadian rhythm, so best to avoid both practices,” Bhatt adds. The American Heart Association's statement points out that current research on circadian rhythms is limited because it is primarily based on only small studies conducted in highly controlled lab settings. As technology advances with wearable devices and artificial intelligence that could help track patterns like skin temperature and heart rate over 24 hours, for example, future research may determine if interruptions in our biological clocks are not only linked but may also be the cause of disease. “We hope this statement will shine a light on the importance of the internal clock and stimulate further research and interest in circadian health and medicine,” adds Knutson.
