Dec. 13 (UPI) -- A combination of 'bad' cholesterol and high blood pressure may increase a person's risk of heart attack or stroke, which are leading causes of death in the United States.
That's according to a long-term study, led by Wake Forest University researchers, of several thousand men and women in the United States.
Its findings were published Tuesday in the journal Circulation.
The researchers found people who have hypertension plus high levels of lipoprotein(a), a type of "bad" cholesterol, may face a 24% higher risk of developing cardiovascular disease and having a major event such as a first-time heart attack or stroke.
In the study, this meant having lipoprotein(a) greater than or equal to 50 milligrams per deciliter, the scientists said. Hypertension was defined as a blood pressure reading of 140/90 mmHg, or the use of blood pressure medication.
By contrast, heart disease risk was not higher among people with elevated levels of lipoprotein(a) but without hypertension, the scientists said.
"High blood pressure is a known cardiovascular disease risk factor, and lipoprotein(a) is a type of inherited 'bad' cholesterol that may also lead to cardiovascular disease," Dr. Rishi Rikhi, the study's lead author and a cardiovascular medicine fellow at Atrium Health Wake Forest Baptist Medical Center in Winston-Salem, N.C., said in a news release.
Previous research has indicated that when a person has hypertension and lipid imbalance, or dyslipidemia, their heart disease risk substantially increases, the release said.
But information has been scarce on how much of an effect lipoprotein(a) may have on cardiovascular disease risk among people with high blood pressure.
Lipoproteins -- which are made up of protein and fat and carry cholesterol through the blood -- have three subtypes: low-density lipoprotein, or LDL; high-density lipoprotein, or HDL, and lipoprotein(a), or Lp(a).
Similar to LDL cholesterol, lipoprotein(a) cholesterol may deposit and build up in the walls of blood vessels, increasing a person's risk of a heart attack or stroke.
For the study, the researchers used health data from the U.S. Multi-Ethnic Study of Atherosclerosis study that began in 2000. MESA is looking into subclinical cardiovascular disease that is discovered prior to clinical signs and symptoms.
At the time of their enrollment, the racially and ethnically diverse group of adults who were participating in MESA were free from heart disease.
The new study included 6,674 MESA participants who had their lipoprotein(a) levels and blood pressure assessed and who had data documenting a cardiovascular disease event such as heart attack or stroke.
Participants were placed into one of four groups: those with lipoprotein(a) levels less than 50 mg/dL and no hypertension; lipoprotein(a) levels greater than or equal to 50mg/dL and no hypertension; lipoprotein(a) levels less than 50mg/dL and hypertension; and lipoprotein(a) levels greater than or equal to 50mg/dL and hypertension.
The scientists then tracked cardiovascular events, including heart attack, cardiac arrest, stroke or death from coronary artery disease, over a follow-up period averaging 14 years. In all, 809 of the participants had such a heart disease event.
Among the two groups without high blood pressure, higher lipoprotein(a) levels did not mean an increased risk for heart attack or stroke, the researchers noted.
And less than 10% of the people in the groups without hypertension had cardiovascular disease events, well below percentages in the two groups with hypertension.
Both groups with hypertension also showed a statistically significant increase in their risk for heart disease events compared with people with low levels of the "bad" cholesterol and no hypertension.
"We found that the overwhelming amount of cardiovascular risk in this diverse population appears to be due to hypertension," Rikhi said in the release.
People with hypertension had even higher cardiovascular risk when their level of lipoprotein(a) was elevated.
"The fact that lipoprotein(a) appears to modify the relationship between hypertension and cardiovascular disease is interesting, and suggests important interactions or relationships for hypertension, lipoprotein(a) and cardiovascular disease, and more research is needed," he said.