Healthy blood pressure is presented by physicians as 120/80; however, there are numerous incidences whereby the blood pressure level rises to 140/90 especially in stressful situations. If blood pressure persists at this level, then physicians diagnose the patient with hypertension.
Studies show that a majority of americans experience a rise in blood pressure with age due to their poor diets and lack of physical activity (Cooper, Rotimi, & Ward, 1999). 25% of these Americans reach the level for hypertension diagnosis. “This accounts for about half a million fatalities per year due to kidney failure, heart disease and stroke” (Cooper, Rotimi, & Ward, 1999).
Studies show that black americans are more likely to suffer hypertension, with the prevalence rate at 35% (Cooper, Rotimi, & Ward, 1999). Additionally, high blood pressure contributes to the death of over 20% of black americans in the united states. Studies show that people from African descent are highly inclined to hypertension due to their genetic makeup.
Cooper, Rotimi, & Ward (1999) claims that this argument is biased because public health research tends to attribute health challenges to racial or genetic features with little or no consideration of other factors such as socioeconomic status. The study by Cooper, Rotimi, & Ward (1999) explores other causes of the disparity between blacks and whites by focusing on other variables with the exception of genetics.
Is the high susceptibility of African Americans to hypertension caused by other factors besides genetics? Does aging increase the susceptibility of African Americans to hypertension? Is it possible to avoid rising blood pressure in the modern life for people of all skin colors? How do environmental and biological risk factors interact to produce hypertension?
Hypertension is caused by intricate “interactions among external factors (such as stress or diet), internal physiology (the biological systems that regulate blood pressure) and the genes involved in controlling blood pressure” (Cooper, Rotimi, & Ward, 1999).
Higher levels of angiotensinogen in the RAAS correspond to high blood pressure.
- Establishment of research stations in various communities in West Africa, South America and North America. The countries selected were Nigeria, Cameroon, Zimbabwe, St. Lucia, Barbados, Jamaica and the U.S.
- Focus of the project on Nigeria, Jamaica and the US: these three countries were selected due to the assumed genetic ties since the Americans in the US and Jamaica are believed to have migrated from West Africa between the seventeenth and nineteenth centuries due to slave trade.
- Black people from different locations were randomly selected for testing to check for hypertension and its common risk factors (e.g. poor diet, obesity and physical inactivity).
The Nigerian community selected was rural, with complex family structures. The residents engaged in strenuous physical activity due to farming activities. “Their diet comprised conventional foods like rice, tubers and fruits” (Cooper, Rotimi, & Ward, 1999). In addition, the community did not have formal records of mortality and life expectancy.
It was observed that malaria is the primary killer in the region, with an adult mortality risk of 2%. Adults who survived to old age were healthy, and it was noted that death due to hypertension was rare. The study also revealed that blood pressure did not rise with age for the blacks in Nigeria (Cooper, Rotimi, & Ward, 1999).
The community selected in Jamaica was a representation of an industrial economy. The community was a former colonial city with a population of close to 100,000 people. The risk of infectious diseases was low, but the prevalence of chronic disease was higher than that of Nigeria. While the family structure in Nigeria was mainly polygamous, that of Jamaica had numerous incidences where women were the providers.
This is because their high poverty levels led to high unemployment rate that caused the marginalization of men; hence, lowering their position in society. The people also engaged in laborious activities, and their diet comprised mostly local foods and modern commercial products. The study revealed that the Nigerian community experiences few cases of heart disease and cancer, with a life expectancy of six more years compared to that of blacks in the US (Cooper, Rotimi, & Ward, 1999).
The US study was conducted in a region of Chicago that comprises mostly African Americans. Most of the older adults were migrants from lower sections of the US. It is possible that their migration to the north enhanced their health and income level due to the job opportunities in the heavily industrialized region. Both genders contribute to the household income. Their diet comprised foods that are high in fat and salt, which are some of the risk factors for cardiovascular disease (Cooper, Rotimi, & Ward, 1999).
“The study group shared a common genetic composition with 75% of the US and Jamaican study population sharing their genetic heritage with the Nigerians” (Cooper, Rotimi, & Ward, 1999). From the study population, it was noted that about 7% of the Nigerian sample population had high blood pressure. Higher levels of hypertension were noted in the Nigerian urban towns. “The study also revealed that 26% of black Jamaicans and 33% of black Americans had high blood pressure or were under medication” (Cooper, Rotimi, & Ward, 1999).
This regional increase was due to a variety of reasons including the steady increase in body mass index from Nigeria to Jamaica to the US. The same increment across various regions was observed in average salt intake. Hence, about 50% of the increased risk of hypertension in American Americans compared with Nigerians was due to their lack of physical activity and poor diet causing them to be overweight (Cooper, Rotimi, & Ward, 1999).
Based on the increasing susceptibility to hypertension as the geographical setting changed, it can be said that the human cardiovascular system has evolved from the rural setting in Africa, where the diet was low in fat, and there was a lot of physical activity. For people who have maintained this lifestyle, there was no increase in hypertension with age, as seen in rural Nigeria.
This provided a suitable control group for comparison in the study of the risk of African Americans to hypertension based on living conditions (environment). Living conditions also accounted for variation in blood sugar level between rural and urban Nigeria, whereby the risk was higher in Nigerian towns.
Environmental and biological causes of hypertension
The role of kidneys in the human body is to regulate the level of sodium ions in the blood stream, which controls blood pressure. The kidneys can hold up to 98% of sodium; however, they also release it back into the blood causing blood pressure.
Absorbing too much sodium also destroys the kidneys’ filtering mechanism, preventing them from adequately regulating the blood sugar levels. To identify the efficiency of the organs in regulating body sodium, an experiment was conducted to evaluate the activity of rennin-angiotensin-aldosterone system (RAAS), which is a vital pathway in the regulation of blood pressure.
RAAS controls the level of protein angiotensin II present in the bloodstream, whose role is to constrict blood vessels causing the pressure to rise. It also promotes the release of aldosterone, which enhances the ability of kidneys to absorb sodium from the blood. To evaluate the activity of RAAS, the experiment assessed the level of angiotensinogen-one in blood, which remains fairly constant.
The study revealed that higher angiotensinogen levels correspond to higher blood pressure. This was supported by the increase in average level of angiotensinogen for the sample population from Nigeria to Jamaica to the US, just as the rate of hypertension increased. The higher level of angiotensinogen was attributed to the risk factors such as excessive body fat and obesity (Cooper, Rotimi, & Ward, 1999).
Increased vulnerability due to genes
Studies show that the 235T gene variant is twice as common in African Americans as it is among the European Americans. This was supported by the fact that 90% of the sample population in Nigeria had the gene variant. However, the presence of the gene did not suggest an increased risk of hypertension since only 7% of the sample was diagnosed with high blood pressure. Hence, the deduction that hypertension is not induced by angiotensinogen levels, but rather physiologic or environmental factors (Cooper, Rotimi, & Ward, 1999).
The assessment of the impact of the environment on the rate of blood pressure on Africans in Diaspora was effective, due to the stability of the gene of the sample population. More studies should be conducted to identify the role psychological and social stress in increasing the rate of high blood pressure across various cultures. Such a study could explore the risk posed by racial discrimination on blood pressure. More research should also be conducted on isolated genetic and environmental effects on hypertension (Cooper, Rotimi, & Ward, 1999).
Cooper, R. S., Rotimi, C. N., & Ward, R. (1999). The Puzzle of Hypertension in African-Americans. Scientific American, 56-62.