BUFFALO, N.Y. -- People with normal blood pressure can experience greater increases in blood pressure during stressful situations if they have high cholesterol, University at Buffalo researchers have found in the first study showing a link between cholesterol levels and hypertension.
Conversely, they found that lowering cholesterol with drugs and diet also lowers stress-related increases in blood pressure.
"We don't know the cause of high blood pressure in 90 percent of hypertensives," said Bong Hee Sung, Ph.D., UB associate professor of medicine and chief investigator on the study, which appears in the June issue of the American Journal of Hypertension.
"These findings shed some light on the mechanisms that cause high blood pressure, opening up possible new avenues for treatment and prevention."
Sung said approximately 12.7 million adults in the U.S. may be candidates for cholesterol-lowering drug therapy.
"Our results indicate that lowering cholesterol may have the added benefit of controlling blood pressure better during stress, which will lower the chances of developing hypertension and heart disease," she added.
High cholesterol is a well-known risk factor for cardiovascular disease, given its role in the formation of plaque that narrows arteries and restricts blood flow. High cholesterol also has been shown to cause the blood vessels to constrict excessively, which may interfere with overall blood-pressure regulation. This effect of cholesterol on vasoconstriction has been well documented in isolated peripheral vessels, Sung noted, but until now, the overall effect of cholesterol on blood pressure has not been studied.
To assess the relationship between high cholesterol and blood pressure, Sung and colleagues established a study group composed of 70 people with normal blood pressure, 33 of whom had normal cholesterol and 37 with high cholesterol. Blood pressure was monitored in both groups while they took a mental arithmetic test, a standard method to simulate psychological stress.
Researchers added stress to the equation, Sung said, because a dramatic increase in blood pressure during physical or mental challenges has been shown to be a risk factor for later development of hypertension and cardiovascular disease. Recent evidence also shows that the damage to organs caused by hypertension is more closely linked to blood-pressure response to stress than to "casual" blood pressure, she said.
Results showed that during the stress test, systolic blood pressure increased to the hypertension range (greater than 140 mm Hg) in 46 percent of the high-cholesterol group, compared to 18 percent of the normal-cholesterol group.
Sung said that high cholesterol appears to impair the ability of the blood-vessel lining (endothelium) to relax and constrict normally. Blood-vessel constriction causes an increase in vascular resistance, which causes an increase in blood pressure.
The study's second phase was designed to determine if lowering cholesterol lowers blood-pressure response to stress. In a double-blind design, half of 26 members of the high-cholesterol group took a cholesterol-lowering drug for six weeks, while the other half received a placebo, and the protocols then were reversed. Total cholesterol fell 26 percent during drug treatment .
Participants repeated the mental arithmetic stress test after both the drug and placebo periods. Results showed that peak systolic blood pressure during stress dropped from 141 mm Hg without treatment to 133 mm Hg after treatment.
Sung's co-authors on the study were Joseph L. Izzo, Jr., M.D., UB professor of medicine and professor of pharmacology and toxicology, and Michael F. Wilson, M.D., UB professor of medicine.