You know that cardiovascular disease is the number one cause of death in both men and women. Did you know that most adverse cardiovascular events occur in the morning, and that people who have a heart attack in the morning are more likely to be seriously affected? Why is that? Researchers from Brigham and Women’s Hospital (BWH) and Oregon Health & Science University have discovered that your internal body clock may contribute to the morning peak in heart attacks and strokes. heart-attack

“Our findings suggest that the circadian system, the internal body clock, may contribute to the increased risk for cardiovascular events in the morning,” said Frank A.J.L. Scheer, PhD, director of the Medical Chronobiology Program at BWH.

Earlier research demonstrated that our body clocks regulate platelet function and cause a peak in platelet activation during the morning hours. A high level of platelet activation can lead to heart attack and stroke by increasing your risk of blood clots. The current study may shed further light on this worrisome pattern.

Over the course of the study, 12 healthy adult volunteers at BWH were assessed throughout a two week laboratory protocol designed to track the levels of Plasminogen activator inhibitor-1 (PAI-1). PAI-1 inhibits the breakdown of blood clots. The study found a robust circadian rhythm in levels of PAI-1, with peak levels occurring at approximately 6:30 a.m. This morning increase in blood clot risk corresponds to the morning increase in adverse cardiovascular events.

The researchers also sought to test whether a morning peak in PAI-1 is caused by the internal circadian system or by other behaviors that typically occur in the morning, such as altered posture and various physical activities. “Our findings indicate that the human circadian system causes a morning peak in circulating levels of PAI-1, independent of any behavioral or environmental influences,” explained Steven A. Shea, PhD, director of the Oregon Institute of Occupational Health Sciences. Scheer added, “Indeed, the circadian system determined to a large extent the PAI-1 rhythm observed during a regular sleep/wake cycle. This morning peak in PAI-1 may thus help explain adverse cardiovascular events in vulnerable individuals.”

These studies establish the circadian rhythm of PAI-1 in healthy individual, but more research is required to know how this rhythm affects more vulnerable individuals, such as those with existing cardiovascular disease.

Researchers hope this is another step in lowering the risk of adverse cardiovascular events during morning hours. In the meantime, healthy sleep habits are recommended, as well as standard protocol related to diet and nutrition, exercise, stress management and other personal risk factors, such as smoking, obesity, high cholesterol, diabetes and high blood pressure.

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