Blacks Blood Pressure Link Sought
DALLAS (AP) _ Healthy blacks don’t react as strongly as whites to a chemical that helps the body handle stress, according to a study that could help explain why blacks are more likely to have high blood pressure.
Many doctors have long blamed poor diet and lifestyle choices for the prevalence of high blood pressure. But the study, published Thursday in Hypertension, a journal of the American Heart Association, offers a physiological possibility.
``Hypertension is probably caused by several factors,″ said Dr. Julio A. Panza, lead researcher. ``Other studies have reported that blacks have increased sensitivity to salt.″
The researchers at the National Heart, Lung and Blood Institute said that blacks aren’t as strongly affected as whites by the chemical nitric oxide, which helps blood vessels relax and carry more blood to muscles during mental stress.
Panza said more research is needed into the role of nitric oxide _ his study used only 12 blacks and 14 whites. But he is optimistic it will lead to earlier identification of people likely to develop high blood pressure and maybe the development of drugs to treat it.
High blood pressure is a leading risk factor for heart disease, heart attacks, stroke and diabetes. Yet, doctors are able to pinpoint the cause of high blood pressure in only about one in 10 patients.
A doctor with the American Heart Association said the study is significant because none of the test subjects had high blood pressure.
That hints strongly at some physiological difference between blacks and whites, said Dr. Roxanne Rodney, associate director of nuclear cardiology at Columbia Presbyterian Medical Center and an associate professor at Columbia University in New York.
``Most of the previous work has been done with medicines, diet and exercise,″ Ms. Rodney said. ``Those factors are all important, but I think we need to get beyond that and see if there are actual cellular differences.″
Not only are blacks about 40 percent more likely than whites to have high blood pressure, they also tend to develop it earlier and more severely.
``This study is certainly in line with the theory that something is going on in blacks that leads to tighter blood vessels,″ said University of Maryland researcher Dr. Elijah Saunders. He also believes environmental factors, including stress from poverty, might explain the prevalence of high blood pressure in blacks.
Ms. Rodney worried that blacks might interpret the study as meaning they are destined to develop high blood pressure.
``Even though there might be tendencies, you can definitely lower your blood pressure by exercise, not eating a high-fat diet and not smoking,″ she said.
In the study, Panza and his colleagues at the heart institute measured forearm blood flow in blacks and whites working on math problems. Blood flow increased more than twice as much in whites as the stress was increased by giving the test subjects harder problems.
Panza repeated the experiment after giving the subjects a drug that cuts the body’s production of nitric oxide, the body’s own mechanism for handling stress.
Whites’ blood flow dropped sharply, but blacks’ blood flow hardly changed, indicating less reaction to nitric oxide, he said.
Panza said further study is needed to understand why blacks might not respond as much to nitric oxide.