"The human body maintains a balance of blood pressure and blood flow by expanding or contracting blood vessels," says Virend Somers, M.D., Ph.D., a Mayo Clinic cardiologist and leader of the study. "Much of this expansion is directed by a layer of cells called the endothelium, which lines the blood vessels. Risks of sudden death, heart attack and stroke are 30 to 50 percent higher in the early morning hours, so we wanted to determine whether the endothelium's effects are diminished in the morning."
The study examined the blood vessel expansion caused by the endothelium in 30 normal, healthy volunteers who were nonsmokers. Measurements were taken at bedtime, and then at 6 a.m. and 11 a.m. Endothelial function was reduced by more than 40 percent in the early morning reading; by late morning it had returned to normal.
"Doctors have known for years that the morning hours are prime time for cardiovascular events such as heart attacks, sudden death and stroke, but the reasons are unclear," says Dr. Somers. "These latest findings may provide clues to the clustering. In fact, the early morning function of the blood vessels in healthy young subjects approaches the levels seen in smokers and diabetic people.
"We are not sure yet how these changes relate to people with cardiovascular disease, but this reduced morning function of the endothelium may be among triggers that could cause an event. We will continue to explore the underlying mechanisms," Dr. Somers concludes.
Other authors of the study include Maria Otto, M.D., Ph.D., Ann Svatikova, Rodrigo Barretto, M.D., Simone Santos, M.D., Michal Hoffmann, M.D. and Bijoy Khandheria, M.D.