Disposition to Diseases Among Blacks in the Diaspora
Summary When Compared to other ethnic groups,
epidemiological evidence for blacks who live in the diaspora suggest an
increase in prevalence for a number of diseases viz. hypertension, diabetes,
prostate cancer, HIV, Trichomoniasis, sickle cell disease and hepatitis C.
Besides the genetic predisposition which may be a contributive factor, there
are sociodemographic factors such as lower standards of education and income,
along with dietary patterns which accentuate the risk within this ethnicity. Introduction Peoples of African descent primarily
originating from the Sub Sahara, have significant populations in the Caribbean,
North and South America, including the United Kingdom. Among this ethnicity,
there is an apparent increase in prevalence of hypertension and its’ related
cardiovascular effects, diabetes, prostate cancer, HIV, Trichomoniasis, sickle
cell disease and hepatitis C. This article represents a review of the
literature reflecting the predisposition that we are subjected to in the
diaspora. The observed racial disparity for the
predisposition to these diseases appears to be genetically based, however,
there are lifestyle and sociodemographic factors which need some consideration.
Within the American context, African
Americans have a lower dietary potassium intake, significantly lower median
income and education, and are less likely to have private group insurance
compared with non-African Americans, while a greater proportion are disabled,
unemployed, in receipt of Medicaid, unmarried, divorced and separated (Table
1). These social circumstances, lead to a lack of resources, knowledge and
access to care, which in turn influence treatment efficacies. [1,2,3]
Table 1: Risk Factors Among Blacks in the Diaspora Increased frequencies Reduced frequencies obesity education basal metabolic index
(BMI) median income impaired vascular
response private group insurance impaired salt excretion access to health care salt sensitivity available resources disabled knowledge unemployed stop smoking unmarried renin divorced dietary potassium separated smokers medicaid recipients Hypertension Hypertension is a serious issue in
black populations as studies reveal that
people of African descent in North and South America have higher mean
blood pressures and higher rates of hypertension than populations of European
descent or populations in Africa. Whether examined within or between
populations, there is an interaction between skin color and socioeconomic
status (SES) in relation to blood pressure, with persons of dark skin color and
low SES having the highest blood pressures.[4] 33% of adult African Americans are
hypertensive, and this ethnicity suffer disproportionately high morbidity and
mortality as compared with whites, earlier onset, and possibly more cardiovascular
risk factors associated with hypertension than other American ethnic groups. Also, African American
women have a higher body mass index (BMI) and reported higher rates of
hypertension, angina, and diabetes.[1] Studies of hypertensive
pathophysiology in black patients indicate that low renin profiles, salt
sensitivity, and impaired salt excretion are more prevalent, while white
patients tend toward moderate to high renin levels. [5] With respect to
antihypertensive therapy, the Joint National Committee on Prevention,
Detection, Evaluation, and Treatment of High Blood Pressure (JNC V), advises
low doses of a thiazide diuretic as the agent of first choice for hypertensive
black patients. When ß blockers are used as first-line therapy, they are less
predictable than diuretics in black patients, however, labetalol is equally
effective in both black and Caucasian populations. Calcium channel blockers
are also an excellent choice for black patients with salt
sensitivity, especially those who are not responsive to diuretics. On the other hand, for
those patients who cannot take thiazide diuretics or calcium channel blockers,
angiotensin-converting enzyme inhibitors and ß blockers may be useful to lower
blood pressure, even though studies indicate that these agents may not be quite
as effective. The apparent minimal
efficacy observed with nitrates in black Americans is due to an impairment of
adequate vasodilation, while there may be an impaired vascular response to the
ß receptor agonist isoproterenol. In a prospective study
utilizing six categories of antihypertensive agents among black patients,
diltiazem produced the best blood pressure control, with a 64% rate of
response. Considering the
armamentarium of antihypertensive medications available, most hypertensive
black patients will need two or more medications to attain adequate blood
pressure control, as only 46% of black patients achieved a diastolic blood
pressure <90 mm Hg while on one antihypertensive medication.[,6] Smoking One of the risk factors for
hypertension is smoking, and data indicates that the rate for inner-city
African Americans is higher than in the general population (45% vs. 25%), and
they attempt to quit smoking more frequently, but their success rate at
quitting is 34% lower.[5] Kidney disease African Americans have a
higher risk for chronic kidney disease (CKD), with one study revealing that the
incidence being 2.7 times higher than whites. Specifically, middle-aged
African-Americans were 4.23 times more likely to develop CKD than their white
peers, while among older adults, the risk for African-Americans was 27%.
Investigators pointed out that "much of the racial disparity in CKD in the
United States is explained by potentially modifiable sociodemographic,
lifestyle and clinical factors such as diabetes mellitus and
hypertension". [3] Vascular nephropathies such as
arterionephrosclerosis are a steadily increasing cause of end-stage renal
failure, and this is especially true for blacks in whom hypertension and
nephrovasculopathies are a major cause of renal insufficiency. There is the
consideration that nephroangiosclerosis might stem from a genetic defect in the
renal vascular bed and that this defect is strongly associated with the
hypertensive trait. [7] Diabetes When compared to Caucasians, African
Americans have a higher dietary fat consumption, and obesity
is more prevalent in black women as compared to other black or white adults.
Hence it is not surprising that among African-American women,
diabetes is considered epidemic; the rate is 11.8% among women ≥ 20 years
of age, and 25% among women > 55 years of age. This is nearly twice the rate
of Caucasian women. In addition, African-Americans
experience higher rates of diabetes-related complications, such as nephropathy,
lower extremity amputations and retinopathies. The frequency of diabetic
retinopathy is 40–50% higher, and end-stage renal disease is four times more
likely among African Americans than Caucasians. In the United States, people of black
African descent with diabetes have 2 to 3 times the amputation risk compared to
whites and it is being suggested that this may be due to differences in care or
pathophysiological characteristics.[8] In the United Kingdom on the other
hand, where care delivery is more equitable, diabetes-related amputation rates
in African Caribbeans vs Europeans found no ethnic difference among women, but
in men, amputation risk was one third that of Europeans. This was wholly
accounted for by low smoking, neuropathy, and peripheral vascular disease
rates. [7] Moreover, the overall mortality rate
among African-American diabetic women is 40% higher compared with their
Caucasian counterparts. [8] Stroke Individuals of African Caribbean
descent who live in the United Kingdom have an increased risk of stroke. The
reasons are not fully understood, however,
differences in genetic predispositions or other novel stroke risk
factors could play a role. One of the possible risk factors could be the
increased incidence of common carotid artery wall thickness or intima-media
thickness (IMT), which is also found among US blacks. [9] When comparing females, African American women have a higher prevalence of stroke,
and their life expectancy is 6 years less than white women. [2] One study determined the role of
prothrombotic polymorphisms in the early onset of arterial Ischemic stroke or
cerebral venous thrombosis (CVT) in a group of young Brazilian adults of
Caucasian and African descent. Brazilians of African descent demonstrated
significant elevations, being 10.3% homozygous for the thermolabile
methylenetetrahydrofolate reductase MTHFR-T.[10] Prostate Cancer Considering the
distribution of trinucleotide CAG sizes in men from African American ethnic
background, whites, or Asians living in Los Angeles County, one study revealed
that at any cutoff, African American men had a much higher quantity of androgen
receptors with shorter CAG repeats followed by whites, then Asians, in a manner
very similar to their relative risk of getting the disease. This CAG repeat
translates in a polyglutamine repeat in the protein, and consequently, it is
hypothesized that it has an effect in the phenotypic function of the protein. [11]
While studies have implicated alleles
at the CAG and GGC trinucleotide repeats of the androgen receptor gene with
high-grade, aggressive prostate cancer disease, little is known about the
normal range of variation for these two loci which are separated by about 1.1
kb. Results reveal that populations of African descent possess significantly
shorter alleles for the two loci than non-African populations (P<0.0001). [12]
A very high screening-detected
prevalence of prostate cancer was obtained in
the predominantly Afro-Caribbean population in Tobago. Elevated PSA
and/or abnormal DRE were observed in 31% (759 of 2484) overall, and in age
groups 40-49 (10%), 50-59 (28%), 60-69 (45%), and 70-79 (64%). 38% of 681 men
biopsied, or 10% of the 2484 screened, were diagnosed with prostate cancer.
These data support the hypothesis that populations of African descent share
genetic and/or lifestyle factors that contribute to their elevated risk for
prostate cancer. [13] There are intra and interracial
differences in prostate cancer incidence and mortality rates worldwide, and
environment and migration patterns seem to influence the disparities in cancer
statistics. The lowest incidence rate is recorded in Chinese, followed by other
Asians, South Americans, southern Europeans, and northern Europeans, in
ascending order. However, people of African descent have the highest incidence
so far. African Americans in Alameda County (California) had incidence rates of
(160/1000,000), while 314/100,000 was reported in African Caribbeans from
Jamaica. [12] Hepatitis
C Hepatitis C infection is the most
common cause of chronic liver disease and is the most common indication for
liver transplantation. Serious sequelae of hepatitis C infection include
cirrhosis, liver failure, and hepatocellular carcinoma. In the United States,
40% of chronic liver disease is related to hepatitis C, and while the highest
rate is in persons aged 30-49 years, hepatitis C is more prevalent in blacks than
in other racial groups. (Figure 1) [14]
Figure 1. Prevalence of HCV infection by age and race/ethnicity in the
United States, 1988-1994. HCV, hepatitis C. Centers for Disease Control and
Prevention. MMWR Recomm Rep.
1998;47(No. RR-19):1-39. HIV
and Trichomoniasis African-Americans make up
just 12% of the population in the United States, but they account for an
estimated 54% of all new HIV infections. Among African-Americans, young women,
gay and bisexual men are at greatest risk of HIV infection. [15] In many jurisdictions in
the United States, HIV is increasingly affecting low-income groups,
particularly African-Americans and women. In fact, the Center for Disease
Control (CDC) estimates that of all new HIV infections in women, 64% are among
African-American women, and it has hypothesized that part of this phenomenon
may result from the amplifying effect of T.
vaginalis. The available
data suggest that T. vaginalis is a
highly prevalent infection, and for
each study that has presented information on ethnicity, the prevalence of Trichomonas has been highest in
African-Americans (23%-51%), ranging from approximately 1.5 to nearly 4 times
greater than other ethnic groups. In several studies in which very high
prevalences of infection were observed, the population consisted exclusively or
predominantly of African-Americans.
The apparent elevated rate
of trichomoniasis in black women may be indicative of a high prevalence of Trichomonas infection among their sex
partners, and lower use of condoms because of a higher frequency of condom
breakage and slippage. Drug use, its association
with high-risk sexual behaviors, including trading sex for money or drugs,
along with douching, which is reportedly more common in black women, (which can
increase susceptibility to other STIs), could predispose to trichomoniasis and
explain the observed racial association. It could also reflect lack
of access to care and distrust of the health-care system, which could manifest
as failure to seek care, noncompliance with treatment recommendations, and
hesitation to refer partners for treatment. [16] Sickle
Cell Disease Sickle cell disease is a recessively
inherited condition in which synthesis of haemoglobin is abnormal. The disease,
which occurs mainly in people of African, African-Caribbean, Indian,
Mediterranean and Middle Eastern descent, is characterised by chronic anaemia,
susceptibility to infection, bouts of severe pain and organ dysfunction. [17] Homozygous sickle cell anaemia (Hb S)
is the most common major haemoglobinopathy in the United States, occurring in
approximately 1 in 626 African Americans. [18] Systemic
Lupus Erythrematosus (SLE) SLE has a high prevalence in Afro-Caribbean
populations. The prevalence of SLE in women in an area of south London was
estimated it to be 177/100000 (95% CI 135-220) in Afro-Caribbeans, 110 (58-63)
in West Africans, and 35 (26-43) in Europeans, suggesting a genetic
predisposition. [19]
Bibliography