TUESDAY, June 1, 2004 (HealthDayNews) -- A daily decrease in the flexibility of blood vessels may be the reason that most heart attacks and strokes strike in the early morning.
That's the conclusion of a Mayo Clinic study in the June 1 issue of Circulation.
"The human body maintains a balance of blood pressure and blood flow by expanding or contracting blood vessels," study leader and cardiologist Dr. Virend Somers said in a prepared statement.
"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," Somers said.
The study included 30 healthy nonsmokers. Their endothelial function was measured at bedtime, 6 a.m. and 11 a.m. The results showed their endothelial function was reduced by more than 40 percent in the early morning but was normal again by later morning.
Early morning endothelial function in these healthy subjects was similar to that seen in smokers and people with diabetes.
"We're not sure yet how these changes relate to people 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," Somers said.
The American Heart Association has more about heart attack.