African American Blood Pressure: Differences between Blacks and Whites
One of the more puzzling medical phenomena is the question of why African Americans have a significantly higher incidence of disease and death related to high blood pressure than everyone else in the world. Up till now, research has been devoted to a macroscopic view of diet, exercise, genetics and social factors. Today, however, researchers are publishing data that is the result of looking into the cause of high blood pressure in African Americans with a much more microscopic view at the cellular level. What they found was that there are significant differences between how cells in the blood vessels of African Americans respond to inflammation in comparison to the same type of cells in Caucasians.
Blood Pressure Facts and Numbers
High blood pressure is a major risk factor of heart disease and stroke, which are the first and third leading causes respectively of death in the United States. Approximately 1/3 of the U.S. population has high blood pressure. High blood pressure is typically defined as having a systolic reading of 140 mm Hg and higher or a diastolic reading of 90 mm Hg and higher. One-quarter of the population is pre-hypertensive, meaning that while their blood pressure numbers do not qualify as high enough to meet the criteria of high blood pressure, they are still higher than normal and need to be monitored. People who are pre-hypertensive are usually labeled as “borderline” by their physicians.
Gender and Race Differences in Hypertension
Compared to women, men under the age of 45 are disproportionately affected by high blood pressure. However, by the time both sexes reach 65 and over, the proportions switch as an increase in women with hypertension outpaces the men.
The prevalence of hypertension in blacks in the United States is among the highest in the world and is increasing. African Americans develop high blood pressure more often, and at an earlier age than whites do. According to recent statistics by the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, compared to Caucasians, African Americans 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. They also found that within the African American community, rates of hypertension vary substantially. Those with the highest rates are more likely to be middle-aged or older, less educated, overweight or obese, physically inactive and are more likely to have diabetes. Those with the lowest rates are more likely to be younger, but also overweight or obese.
Published this month in the journal Vascular Health and Risk Management, researchers report the effects of an inflammatory agent on the endothelial cells that line the inside of the walls of blood vessels. The agent is called Tumor Necrosis Factor-alpha (TNF-α), which is a protein manufactured by white blood cells in response to the detection of damaged cells. TNF-α is a natural component of the immune system and will cause damaged cells to release endothelial micro-particles into the blood stream. Previous studies have shown that individuals with high blood pressure have increased levels of micro-particles in their blood.
When comparing the results between endothelial cells of African Americans and Caucasians, the researchers discovered that the cells from African Americans demonstrated a 90% increase in micro-particle release as opposed to cells from Caucasians that showed only an 8% increase. According to lead author Michael Brown, "It appears that the endothelial cells in African Americans are more susceptible to the damaging effects of this inflammation."
Future Directions in Blood Pressure Research
Brown is currently testing whether exercise may reverse or prevent the damaging effects of high blood pressure on endothelial cells, with an eye toward individuals who are pre-hypertensive. Brown states that, "In our human study we have pre-hypertensive African-Americans, and we find this level of endothelial impairment. Knowing so early how inflammation can affect cells means we can be at a place to intervene before they go on to develop hypertension. That intervention could be lifestyle modification, diet and exercise to improve vascular health." Dr. Brown is the director of the Hypertension Molecular and Applied Physiology Laboratory at Temple's College of Health Professions and Social Work.
Source: Racial differences in tumor necrosis factor-α-induced endothelial microparticles and interleukin-6 production, Authors: Brown MD, Feairheller DL, Thakkar S, Veerabhadrappa P, Park JY. August 2011 Volume 2011:7 DOI: http://dx.doi.org/10.2147/VHRM.S22930