Well Being: Temple researcher explores high blood pressure among African Americans

Temple researcher Michael Brown is studying why African Americans have a greater tendency to develop high blood pressure.
Temple researcher Michael Brown is studying why African Americans have a greater tendency to develop high blood pressure. (RON TARVER / Staff Photographer)
Posted: December 19, 2011

Michael Brown tries to do all the right things. He exercises four times a week on an elliptical trainer at the Philadelphia Sports Club. He lifts weights to keep his muscles toned. Thanks to his wife, Tonya, a vegetarian for 14 years, Brown follows a diet that is 90 percent vegetarian. He eats plenty of vegetables and tofu, a little chicken and turkey occasionally, but no red meat.

"I'm trying to do all I can do to stay healthy," Brown says, "but it's been a battle."

For all his good habits, Brown, 52, is borderline hypertensive. His blood pressure typically ranges between 130/80-90. Blood pressure of 120/80 or less is considered ideal.

His problem is primarily genetic. Brown is of mixed race. His father, Harold, is African American, and the rate of hypertension among African Americans is higher than among Americans of Caucasian descent. In the United States, 41 percent of blacks have high blood pressure compared with 27 percent of whites.

Hypertension is prevalent on his father's side of the family. Brown's paternal grandmother had a stroke, and aunts, uncles and especially his father have struggled with hypertension throughout their lives. In his early 60s, his father suffered a heart attack, and a stent was inserted in one of his arteries. Harold Brown has been taking blood thinners and blood-pressure medication for years.

As for Michael Brown himself: "So far, I've been able to stay healthy with regular exercise and a prudent diet."

Brown's interest in hypertension is professional as well as personal. He's a biomedical researcher at Temple University with a Ph.D. in exercise physiology from the University of Maryland. His subspecialty is lifestyle modification. He is also an associate professor in the Cardiovascular Research Center at Temple's medical school.

Exploring the causes of hypertension has fueled Brown's research for the last 10 years. In August, Brown and four Temple colleagues published the results of a yearlong peer-reviewed study in the journal Vascular Health and Risk Management. The study was unique, Brown says, in that it attempted to examine the hypertension disparity between U.S. blacks and whites on a cellular level.

"This was an opportunity to really drill down to see if there's some reason or explanation at the most basic level," Brown says.

Our blood vessels are lined with endothelial cells that control how the vessel walls react and whether they remain open, relaxed and supple. In the study, Brown and his colleagues found that when endothelial cells from African Americans were stimulated with an inflammatory protein, there was an 89 percent increase in the production of endothelial microparticles, which are indicators of damage and often a precursor to hypertension. Among Caucasians, the increase was only 8 percent.

In another phase of the study, the endothelial cells from African Americans were shown to be much more vulnerable to oxidative stress - the damage caused to cells by free radicals, a by-product of the body's interaction with oxygen.

Brown's study involved cell lines from six subjects - three African American and three Caucasian, so he emphasizes that the sample is small and the findings preliminary. Nevertheless, the disparity between blacks and whites in the potential for what scientists call endothelial dysfunction, which can lead not only to hypertension but also atherosclerosis, strokes and heart attacks, is dramatic, he says.

"The take-home message is this: Even in human studies of pre-hypertensive African Americans, we find that systemic inflammation and endothelial impairment are high."

Bo Fernhall, professor and dean of the College of Applied Health Sciences at the University of Illinois at Chicago, calls Brown's study "highly significant."

"We've known for quite a while that there's a difference between African Americans and Caucasians in regards to how well their endothelial cells function" and how well their blood vessels are able to widen, Fernhall says. "At the cellular level, we haven't been able to understand why this is so, so this study offers good insight into possible mechanisms. That's very important for future research and the potential development of new medicines and treatments."

In general, whites and blacks are remarkably similar in genetic makeup, Brown says, but there are subtle differences that may be exacerbated by environmental factors. In Africa, blacks who maintain traditional lifestyles have few problems with high blood pressure. By contrast, blacks in the United States seem to be more sensitive to salt and are more likely to be overweight.

The prevalence of hypertension in African Americans is among the highest in the world, Brown says. Compared with whites, blacks develop high blood pressure earlier in life. They have a 1.3-times greater rate of nonfatal stroke, a 1.8-times greater rate of fatal stroke, a 1.5-times greater rate of heart disease death, and a 4.2-times greater rate of end-stage kidney disease. As much as 30 percent of all deaths in hypertensive black men and 20 percent of all deaths in hypertensive black women may be caused by high blood pressure, Brown reports.

Brown's focus is on ways to intervene through lifestyle modification - specifically, diet and exercise.

"It's about prevention of a problem early on," he says. Accordingly, he recommends a low-fat, low-carbohydrate diet and consuming foods rich in omega-3 fatty acids, which are salutary for the blood vessels and are available in fish oil, flaxseed, and some nuts.

As for physical activity, he recommends low-intensity aerobic exercise. Interestingly, it may be, in his words, "the most impactful on endothelial cells." As blood flows through veins and arteries, it creates shear force. The more vigorous the activity, the faster blood flows, and the more shear stress. Brown is investigating what level of shear stress is optimal. Low-intensity exercise may be superior, he believes, stimulating the endothelial cells and bathing them with nutrients without inflaming or injuring them.

The good news: "Your genes are not a death sentence. You have a great deal of control over whether you develop hypertension and other cardiovascular problems." Brown says. "And you don't have to be an Olympic athlete to benefit from the low-intensity exercise that seems to be most effective. Just walking vigorously can make a world of difference."


"Well Being" appears every other week, alternating with Sandy Bauers' "GreenSpace" column. Contact Art Carey at acarey@phillynews.com. Read his recent columns at www.philly.com/wellbeing.

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