“Substantial evidence has accumulated from a wide range of studies demonstrating the critical role the circadian system plays in human health,” says Kristen Knutson, PhD, a coauthor of the new statement and an associate professor of neurology at Northwestern University’s Feinberg School of Medicine in Chicago.
Here’s what the evidence shows about the link between circadian rhythms, heart health, and metabolism.
The Relationship Between Your Circadian System and Heart Health
Circadian rhythms help regulate heart rate, blood pressure, metabolism, and hormone secretion, including cortisol, which is important for stress response and metabolism, the statement explains.
It defines circadian health as “the optimal function, rhythmical character, and alignment of the circadian system with the light-dark cycle.” The body calibrates its circadian system via light detected by the eye and transmitted to the brain, which sets the rhythm of the body’s internal clock.
The statement outlines several factors that can affect the alignment of your circadian system:
- Light Exposure Light helps synchronize your internal clock, so morning exposure to light can reinforce a healthy circadian rhythm. Nighttime artificial light (especially blue light from screens) suppresses the body’s production of the sleep-regulating hormone melatonin and delays sleep. Too much nighttime light exposure is also tied to an increased risk of heart disease.
- Meal Timing Eating late at night or having irregular mealtimes disrupts the circadian rhythms of your organs, including the liver and pancreas, which can cause blood sugar spikes or dips and weight gain. Eating earlier in the day (for example, having breakfast before 8 a.m.) is linked to a lower risk of type 2 diabetes and better heart health and weight.
- Physical Activity Timing Exercising in the morning or afternoon can keep the biological clock running as it should; evening workouts can throw it off. Exercise timing can also influence blood pressure, blood sugar control, and sleep quality. However, the authors noted that more research is needed to determine the optimal exercise time for different people.
- Shift Work, Light Pollution, and Inconsistent Sleep Working nontraditional schedules might expose someone to light pollution, irregular mealtimes, and inconsistent sleep habits compared with people with traditional day-night schedules. This can increase the risk of heart disease.
- Individual Internal Clocks Being a night owl or an early bird affects how people respond to light, meals, and exercise. AHA’s statement suggests that tailoring interventions to someone’s natural internal clock could improve circadian alignment, but “assessing true circadian rhythm is challenging.”
Why Good Sleep Matters to Your Heart
“Sleep quality and overall cardiovascular health have been intimately tied together for a long time, and it’s nice that it’s being called out,” says Andrew Freeman, MD, a cardiologist at National Jewish Health in Denver, who wasn’t involved in creating the AHA statement.
Dr. Freeman emphasizes the vital role of sleep and sleep quality to his patients, along with exercising regularly and eating a healthy, mostly plant-based diet, which also impacts sleep.
He says seven to nine hours of uninterrupted sleep has been associated with a decreased risk for heart problems, especially when you can stick to a consistent sleep schedule.
Ultimately, the new AHA statement “emphasizes the importance of the circadian system, which is different from sleep itself,” Dr. Knutson says. “We know that there are several components of a healthy lifestyle, including diet, exercise, and sleep. Circadian health emphasizes that the timing of these behaviors is an important characteristic in addition to amount and quality.”
How to Keep Your Circadian Rhythm in Sync
“We all need to think about the consistency of our sleep timing if we seek optimal health,” says Chris Winter, MD, a neurologist and sleep specialist in Charlottesville, Virginia. Dr. Winter was not involved with the AHA statement, but says it represents another scientific body recognizing the importance of sleep to your health.
- Stick to a regular bedtime and wake-up time.
- Get outside in the morning.
- Exercise daily, preferably earlier in the day.
- Avoid alcohol and caffeine in the evenings.
- Limit screen time.
- Avoid naps, especially in the afternoon or evening.
- Create a comfortable sleep environment with your ideal temperature.
