For most individuals, the word circadian—which comes from the Latin phrase circa dame, meaning “about a day”—refers back to the 24-hour cycle that governs once we sleep and wake. But circadian rhythms are hard-wired into virtually every cell within the body, governed by a master clock within the brain that synchronizes clocks in tissues and organs, including the center. Although these clocks are in tune with day by day light-dark cycles, also they are influenced by behavior: sleep, eating, physical activity and stress.
An up-to-date review published on July 15, 2025 European Heart Journal Pulls together the most recent science on how the body's internal clocks regulate the center and blood vessels, and the way disruptions can occur — from disruptive work, poor sleep, or unhealthy habits.
Monday morning heart attacks
As the review notes, heart attacks are thrice more more likely to occur within the morning than within the evening. Dr. Shear's earlier research helped explain why: Among other aspects, levels of a protein that makes blood clot easier peak around 6:30 a.m. and slowly fall over the following 12 hours. Studies also show that heart attacks between midnight and 6 a.m. cause more heart muscle damage and worse long-term outcomes.
Heart attacks usually tend to occur on Mondays than another day of the week. Why? On weekends, people are likely to not sleep longer than usual after which sleep in the following day, which experts call “social jet lag.” On Monday morning, after they should get up again for work, the disconnect between their social and biological clock could cause subtle changes in blood pressure, hormone secretion and metabolism that increase the danger of a heart attack.
The same trend occurs every spring, once we turn our clocks forward an hour for daylight saving time. Heart attacks are also more common in the course of the first week of daylight savings — especially that first Monday after the switch.
Best time to eat and exercise?
Many studies show that folks who work night shifts experience higher rates of heart problems, possibly due partially to circadian misalignment. But just eating in the course of the day — before and after their shift — may also help shift staff avoid this risk, as Dr. Shear's team reported within the April 8, 2025, issue of Nature Communication. Their previous research showed that eating at night increases levels of hunger hormones and in addition causes a surge in hormones and slows metabolism, which can explain the increased risk of obesity in individuals who eat more at night than in the course of the day.
Popular advice cautions against exercising late within the day, especially at night, because exercise's increased heart rate and body temperature could make it harder to go to sleep. While this will likely be true for intense exercise inside an hour of bedtime, afternoon and evening exercise lowers blood pressure and levels of cholesterol greater than morning exercise, in response to some research.
“Most evidence supports the benefits of eating earlier in the day but exercising later in the day,” says Dr. Scheer.
Medication time
This review also highlights the concept of chronotherapy. Some medications are already prescribed over time. For example, short-acting statins equivalent to simvastatin (Zocor) and pravastatin are frequently taken at night to match the body's peak cholesterol production. But for more powerful statins like rosuvastatin (Crestor), time doesn't matter. If your blood pressure rises at night or early within the morning, taking blood pressure medication at bedtime may also help offset the harmful morning spike. But up to now, there may be little or mixed evidence that any changes in these times actually make a difference by way of heart-related problems.
What are you able to do?As researchers proceed to enhance our understanding of circadian rhythms, listed below are some steps you may take to remain in sync together with your body's internal clock. Front-load your calories in the primary half of the day. Your metabolism is more efficient than at night. Exercise usually, but time it right. A vigorous workout near bedtime can disrupt sleep, but afternoon and evening workouts will be helpful to your heart. Get some morning sunlight. Exposure to shiny light within the morning helps strengthen your circadian clock. Keep a consistent sleep schedule. Go to bed and get up around the identical time day by day, even on weekends. Limit evening screen time. Blue light from devices can interfere together with your body's preparation for sleep. Discuss the timing of medicines together with your doctor. Ask if the timing of your medications can affect their effectiveness. |
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