Study: Endothelium May Be Factor in Early Morning Heart Attacks, Strokes

Risks of sudden death, heart attack and stroke are 30 to 50 percent higher in the early morning hours. A Mayo Clinic study reported in the June 1 issue of Circulation has found that it may be due to reduced functioning of the endothelium that people commonly have during these hours.

“The human body maintains a balance of blood pressure and blood flow by expanding or contracting blood vessels,” said 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.”

The study examined blood vessel expansion caused by the endothelium in 30 normal, healthy volunteers who did not smoke. After taking measurements at bedtime and again at 6 a.m. and 11 a.m., the researchers found a reduction in the participants’ endothelial function by more than 40 percent in the early morning reading. By late morning, their endothelial function 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.”

Somers said he and his colleagues are not yet sure how these changes relate to people with cardiovascular disease, but he added that the reduced morning function of the endothelium may be among triggers that could cause an event. “We will continue to explore the underlying mechanisms,” he concluded.

Other sources: Mayo Clinic