Hypertension treatment and control in sub-Saharan Africa: the epidemiological basis for policy.
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Adult↗
Biomedical subjects
C N Rotimi
Publications and source records attributed to C N Rotimi.
Weight-height relationships among eight populations of West African origin: the case against constant BMI standards.
OBJECTIVE: To ascertain whether constant body mass index (BMI) standards are appropriate in genetically similar populations. DESIGN: Data are taken from the International Collaborative Study of Hypertension in Blacks (ICSHIB), an observational study. SUBJECTS: Individuals of African descent who were included in ICSHIB. Subjects lived in eight different sites: Barbados; Cameroon (urban and rural); Jamaica; Manchester, UK; Maywood, IL; urban Nigeria; and St Lucia. MEASUREMENTS: Weight and height. RESULTS: Constant BMI standards effectively argue for the constancy of slope of the linear regression equations of In(weight) on In(height) across populations. Linear regression results indicate that the height/weight relationship implied by the use of constant BMI standards, is not found in these populations and that there is much variation across groups. CONCLUSION: The use of constant BMI standards in classifying individuals prognostically may be unwise, even in genetically similar populations.
Africa, Western↗
Leptin and body composition of Nigerians, Jamaicans, and US blacks.
The role of leptin in humans remains controversial. Leptin concentrations are highly correlated with body fat stores. We tested whether or not this relation was consistent across the range of body composition encompassing the lean as well as the obese. Individuals participating in community-based comparative research in Nigeria (n = 363), Jamaica (n = 372), and the United States (Maywood, IL; n = 699) had their plasma leptin concentrations and body compositions (with bioelectrical impedance analysis) measured. All participants identified themselves as being black. Body mass index (in kg/m2) ranged from 14 to 62. Large differences in mean plasma leptin were noted across populations for both men and women in Nigeria, Jamaica, and the United States, respectively (men: 2.8, 3.9, and 6.8 microg/L; women: 10.3, 18.6, and 27.7 microg/L). An exponential function fit the relation between percentage body fat or total fat mass and leptin for men and women at each site. For women and men the exponential function with either percentage body fat or total fat mass was of the same shape, but increased by a constant in women, yielding higher leptin concentrations than in men at every level of body fat. On the basis of this broad distribution of body composition, the data suggest an exponential response of leptin to increases in body fat stores, consistent with the development of leptin resistance in individuals developing obesity. These findings likewise confirm that men and women exhibit different set points in terms of leptin production.
Adipose Tissue↗
Association of waist circumference with risk of hypertension and type 2 diabetes in Nigerians, Jamaicans, and African-Americans.
OBJECTIVE: Prior studies have supported that waist circumference correlates better with visceral adipose tissue and is a better predictor of cardiovascular disease than are BMI and waist-to-hip ratio. In this study, we reexamine the role of waist size on the risk of hypertension and type 2 diabetes in African-origin populations from three contrasting environments. RESEARCH DESIGN AND METHODS: A cross-sectional survey was conducted of 5,042 men and women 25-74 years of age from Nigeria, Jamaica, and the U.S. The relationship between waist, blood pressure, and fasting blood glucose was assessed using multiple linear regression analyses. Logistic regression analyses using sex-specific empirical waist cut-points were used to determine the risks of hypertension and type 2 diabetes. RESULTS: Waist circumference was positively correlated with blood pressure and fasting blood glucose (P < 0.05). Increasing waist quartiles were significantly associated with higher risks of hypertension in the three populations, as estimated from age-adjusted odds ratios obtained from sex-specific logistic regression models. A highly elevated risk of type 2 diabetes-10-fold for Jamaican men and 23-fold for African-American women-was observed in the comparison of lowest to highest quartiles of waist circumference. CONCLUSIONS: Substantial reduction in hypertension and diabetes in men and women is achievable if the waist size is decreased in these populations. Intervention programs designed to reduce waist circumference through lifestyle modification, including exercise and diet, may have significant public health significance in reducing the incidence of hypertension and adult-onset diabetes in these populations.
Adult↗
Serum distribution of lipoprotein(a) in African Americans and Nigerians: potential evidence for a genotype-environmental effect.
Differences in lipoprotein(a) [Lp(a)] levels across populations have been described and blacks are known to have higher Lp(a) values compared to whites. However, environmental factors which influence Lp(a) levels have been difficult to identify. We took advantage of the large environmental contrast which exists against a common genetic background between U.S. and Nigerian blacks to examine the relationship between Lp(a) and apolipoprotein(a) magnitude of apo(a) isoforms. Although the distribution of Lp(a) and apo(a) isoforms was nearly Gaussian in both populations, mean serum Lp(a) values were significantly higher in the United States than in Nigeria (20.5 vs. 12.7 mg/dl; P = 0.0001) and U.S. blacks had a higher frequency of the large molecular weight isoforms compared to Nigerians. Similar trends in the relationship between apo(a) isoform and Lp(a) concentration were seen in both populations; however, the magnitude of the effect was different. Compared to the Nigerians, U.S. blacks had significantly higher mean Lp(a) values for the same apo(a) isoform. The association of Lp(a) with low density lipoprotein-cholesterol (LDL-C) level was not significant after correcting for the contribution of Lp(a) cholesterol to LDL-C in both populations. Surprisingly, the association between Lp(a) and total-C remained significant (r = 0.20, P = 0.04) after similar correction for the contribution of Lp(a) cholesterol in the U.S. sample. Understanding the relationship between other factors including lifestyle characteristics capable of influencing total-C may help explain the unusually high Lp(a) level observed in this U.S. population.
Adult↗
Prevalence of NIDDM among populations of the African diaspora.
OBJECTIVE: Rates of non-insulin-dependent diabetes mellitus have risen sharply in recent years among blacks in the U.S. and the U.K. Increases in risk have likewise been observed in the island nations of the Caribbean and in urban West Africa. To date, however, no systematic comparison of the geographic variation of NIDDM among black populations has been undertaken. RESEARCH DESIGN AND METHODS: In the course of an international collaborative study on cardiovascular disease, we used a standardized protocol to determine the rates of NIDDM and associated risk factors in populations of the African diaspora. Representative samples were drawn from sites in Nigeria, St. Lucia, Barbados, Jamaica, the United States, and the United Kingdom. A total of 4,823 individuals aged 25-74 years were recruited, all sites combined. RESULTS: In sharp contrast to a prevalence of 2% in Nigeria, age-adjusted prevalences of self-reported NIDDM were 9% in the Caribbean and 11% in the U.S. and the U.K. Mean BMI ranged from 22 kg/m2 among men in West Africa to 31 kg/m2 in women in the U.S. Disease prevalence across sites was essentially collinear with obesity, pointing to site differences in the balance between energy intake and expenditure as the primary determinant of differential NIDDM risk among these populations. CONCLUSIONS: In ethnic groups sharing a common genetic ancestry, these comparative data demonstrate the determining influence of changes in living conditions on the population risk of NIDDM.
Adult↗
Prevalence of adult diabetes in Ibadan, Nigeria.
Within the framework of an international collaborative network, we measured the prevalence of diabetes mellitus in a traditional Yoruba community in the city of Ibadan, Nigeria. Using a random sampling technique we enrolled a community sample of 247 men and women. Fasting blood glucose (FBG) was measured at the community clinic from a fingerstick using the Companion2 Medisense blood glucose meter. The mean FBG was 4.7 mmol/L and 4.9 mmol/L for men and women, respectively. Using the 1985 WHO criteria, the prevalence of diabetes was 2.8%. There was no significant rise in FBG with age. Compared to the lowest quartile of the body mass index (BMI), there was about a 1.5 fold increased risk of developing elevated FBG. The test of trend between FBG and BMI was however not statistically significant. Despite a modest hypertension rate (22.3%), there was no significant difference in the FBG for hypertensives compared to normotensives. The findings of this study show that the prevalence of diabetes mellitus in this West African community remains low compared to nations in Western societies. However, in comparison to previous estimates from sub-Saharan Africa, the prevalence of adult onset diabetes seems to be on the increase.
Adult↗
The absence of adult mortality data for sub-Saharan Africa: a practical solution.
Information on cause of death among adults in sub-Saharan Africa is essentially nonexistent. Published sources provide statistics on both cause-specific and overall rates of mortality, but closer examination reveals that these data consist mostly of extrapolations and outright guesses. In the absence of accurate and comprehensive registries of vital events for the majority of the region's inhabitants, longitudinal studies of defined population-based cohorts represent the only realistic strategy to fill this void in basic public health information. The advantage of longitudinal studies is particularly clear for chronic diseases, the category for which the least is known. Noncommunicable diseases account for a significant portion of adult deaths in sub-Saharan Africa, yet the empirical bases for public health policies and interventions are essentially absent. Verbal autopsy has great potential to contribute to understanding about the cause of death among African adults. This method is discussed in the present article, and practical considerations for longitudinal studies using this methodology are reviewed.
Adolescent↗
Determinants of hypertension in West Africa: contribution of anthropometric and dietary factors to urban-rural and socioeconomic gradients.
The determinants of hypertension in West Africa have not been well defined. The authors sampled 598 participants aged 45 years or more from a recent population-based survey in southwest Nigeria (190 rural men and women, 205 urban poor men and women, and 203 retired railway workmen). The estimated mean age was 61 (10) years. Mean pressures were low relative to westernized societies: systolic blood pressure = 124 (24) mmHg, diastolic blood pressure = 72 (13) mmHg. Both men and women were remarkably lean: body mass index = 21.3 (3.6) and 23.0 (5.2) kg/m2, respectively. Hypertension prevalence increased across the gradient from rural farmers to urban poor to railway workers: 14, 25, and 29 percent, respectively, had a blood pressure of 140/90 mmHg or greater, and 3, 11, and 14 percent, respectively, had a blood pressure of 160/95 mmHg or greater (p for trend < 0.01 for both cutpoints). On the basis of a 24-hour urine sample, daily electrolyte excretion was 110 (57) mEq of sodium and 46 (24) mEq of potassium. Mean sodium:potassium ratio was 2.6 (1.0) and was higher among the urban residents (p < 0.01) and correlated with systolic and diastolic pressures (r = 0.16-0.18, p < 0.01). These findings provide quantitative estimates of the impact of known hypertension risk factors in West Africa and demonstrate the basis for increased prevalence with urbanization and associated economic and dietary change. These results also provide support for recommendations for prevention in West Africa and provide a benchmark against which to compare populations in the African diaspora.
Aged↗
Obesity and hypertension prevalence in populations of African origin. The Investigators of the International Collaborative Study on Hypertension in Blacks.
Obesity has been shown to be associated with hypertension in Africa, the Caribbean, and the United States, but there has not previously been an opportunity to compare the magnitude of this relation and estimate the contribution of obesity to hypertension risk across these populations. The International Collaborative Study on Hypertension in Blacks (ICSHIB) used age-stratified sampling and a standardized protocol to measure blood pressure and hypertension risk factors. We analyzed data on 9,102 men and women, age 25-74 years, from seven sites. We studied hypertension (140/90 mmHg or medication) in relation to body mass index (BMI) and sex-specific BMI cut-points designating "overweight" and "obesity." The prevalence of these conditions ranged from 6% to 63% for overweight, from 1% to 36% for obesity, and from 12% to 35% for hypertension. Adjusted relative risks were similar in most sites, ranging from 1.3 to 2.3 for both cut-points. We found that 6-29% of hypertension in each population was attributable to overweight and 0-16% to obesity. Comparing rural Africa with the United States, 43% of the difference in hypertension prevalence for women was attributable to overweight, and 22% for men, whereas respective values for obesity were 14% and 11%. These results indicate that the association between adiposity and hypertension is roughly constant across a range of environments, with little evidence for variation in susceptibility to effects of overweight in these groups.
Adult↗
The mortality risk associated with hypertension: preliminary results of a prospective study in rural Nigeria.
The contribution of hypertension to adult mortality in Africa has not been well studied. Although cross-sectional surveys have provided data on the prevalence of this condition, the relative risk of death associated with hypertension has not been defined. In the face of high levels of competing mortality from infectious disease among the general population, and the virtual absence of atherosclerotic precursors, estimates of risk derived from industrialised countries may not be generalisable to this setting. We conducted a 2-year prospective study among 1344 mean and women in a rural community in south-western Nigeria. The prevalence of hypertension (140/90 mm Hg) at baseline was 9.3%. In the observational phase, 3.0% of the survey participants died each year. Among the 74 decedents, hypertension was nearly twice as common as among those who survived (14.9% vs 8.4%). In multivariate analysis the risk of death increased over 60% for a 20 mm Hg increase in diastolic blood pressure. The population attributable risk, or the reduction in mortality that would have been observed if hypertension were not present in this community, was estimated as 7%. These findings document an identifiable impact of hypertension on all-cause mortality in rural Africa and demonstrate that programs to evaluate potential treatment options are needed.
Adult↗
Questions on adult mortality.
The technique of verbal autopsy is being used to investigate the causes of adult deaths in part of Ibadan, Nigeria. The problems encountered in the first year of the study and the measures taken to overcome them are described below.
Adolescent↗
Distribution of anthropometric variables and the prevalence of obesity in populations of west African origin: the International Collaborative Study on Hypertension in Blacks (ICSHIB).
A survey of the prevalence of hypertension and associated risk factors including obesity was carried out among persons of West African heritage currently living in societies at different stages of social, economic and technological development. We present here the distribution of several anthropometric variables and the prevalence of obesity in these populations. Using a standard protocol with centralized training of field staff, 7,439 men and women aged 24 to 75 from six multinational sites were recruited and examined. Although men were taller, women were more obese across sites. Body mass index (BMI) and consequently the prevalence of overweight and obesity increased with westernization from rural African subsistence farming communities to suburban Chicago. Average BMI increased with age until about age 54, and then began to decline or at least level off. The mean BMI for African-American men and women was 27.1kg/m2 and 30.8kg/m2, respectively. Men displayed high levels of centripetal fatness, measured as the waist-to-hip ratio (WHR), compared to the women across site. Based on the US Department of Agriculture guidelines, 22.6% and 56.9% of the African-American men and women had elevated WHR. Although account must be taken of the important contribution of an individual's genetic background, this multinational study of persons with similar heritage clearly shows the potent impact of current environmental factors on the distribution and level of obesity.
Adult↗
Absence of black-white differences in sodium and calcium in platelets.
Consistent differences in sodium transport in red blood cells are observed in blacks compared to whites and have been the basis for speculation regarding physiologic differences in the vascular bed as well. The theoretical link between these metabolic markers and the risk of hypertension generally assumes a secondary effect on calcium. Calcium metabolism in red cells is difficult to study, however, so this proposition has never been tested directly. Given the growing importance of platelets in this area of research, and the availability of sensitive laboratory methods, we carried out a systematic examination of calcium and sodium homeostasis in this cell line among black and white normotensive subjects. No differences were noted in resting cytosolic calcium, mobilizable stores, agonist-induced response, or sodium-calcium exchange. In addition, resting sodium was not different between groups, nor was the increase in sodium induced by ouabain. A correlation of 0.3 was observed between blood pressure and both resting and stimulated cytosolic calcium (P < .05). Red cells may be atypical for studies of calcium and sodium homeostasis, and their relevance for interethnic studies of causal pathways in hypertension should be reconsidered.
Adult↗
Students' attitudes toward university health services.
This study measured students' attitudes toward a university's student health services (SHS) and identified factors that were related to their attitudes. A questionnaire surveying students' attitudes was administered to a sample of 150 students at the Oxford Campus of the University of Mississippi. Analysis of the data revealed that students' attitudes had a statistically significant correlation with the following variables: perceived medical care cost, amount of health information/education received during medical encounters, time spent in the waiting room of the SHS, sex of the student, and income of the student. There was no significant relationship between attitude and age.
Adult↗
Production of aflatoxin by Aspergillus flavus (UBMI) in some Nigerian indigenous beverages and foodstuffs.
Sixteen samples of some Nigerian indigenous beverages and foodstuffs were analyzed for their aflatoxin content. All the eight samples of beverages tested were found to be contaminated with aflatoxin. Of the eight samples of foodstuffs tested, all contained aflatoxin except ewedu, dawadawa and shoko yokoto. All the beverages used as culture media for Aspergillus flavus (UBMI) supported the growth of the fungus and aflatoxin elaboration. A. flavus was found to grow luxuriantly on all samples of foodstuffs, except dawadawa. However, growth of the fungus on foodstuffs was not synonymous with aflatoxin production.
Aflatoxins↗
Prevalence of diabetes and impaired glucose tolerance in Nigerians, Jamaicans and US blacks.
The prevalence of type 2 diabetes, impaired glucose tolerance and associated risk factors were compared in sample surveys in Africa and the Caribbean with the Third National Health and Nutrition Survey (NHANES-III) from the United States. A total of 856 Nigerians, 1286 Jamaicans, and 1827 US blacks were included in the study. Body mass index (BMI) increased in a stepwise fashion across the three populations groups, ie, 23 kg/m2 in Nigerians, 26 kg/m2 in Jamaicans, and 28 kg/m2 in US blacks. The corresponding age-adjusted prevalences of type 2 diabetes among persons aged 25-74, were 1%, 12%, 13%. Jamaican women were found to have the same prevalence of type 2 diabetes as US women (14 vs 13%, respectively); mean BMI was likewise very similar (28 kg/m2 in Jamaican and 29 kg/m2 in US women). BMI and waist-to-hip ratio were both associated with type 2 diabetes prevalence. Findings of this study confirm the marked gradient in type 2 diabetes risk among these genetically related populations and suggest that the blacks in the island nations of the Caribbean and the United States are at particularly high risk. Nigerians exhibited remarkably well-preserved glucose tolerance. Understanding the factors that limit the risk of type 2 diabetes in West Africa, beyond relative absence of obesity, would have considerable public health significance.
Adult↗
The relation of central adiposity to components of the insulin resistance syndrome in a biracial US population sample.
The higher rates of type 2 diabetes mellitus, hypertension, and many others factors of the insulin resistant syndrome (IRS) often seen in African Americans compared to whites do not seem to be explained by differences in central obesity. Reasons for this may be due, in part, to the validity of the commonly used anthropometric surrogate of central adiposity. Recent findings have shown that waist circumference is a better surrogate of total body and visceral adipose tissue and is better correlated with CVD than the traditionally used anthropometric indexes of the body mass index or waist/hip ratios. In this study, waist circumference was employed to determine the association between central adiposity and components of the insulin resistance syndrome in blacks (N=1963) and whites (N=4894) from the US national population-based samples. Sex-specific correlation coefficients were used to estimate the association between waist circumference and factors of the IRS. Multiple linear regression analyses were used to determine racial differences in waist circumference and the independent association of waist circumference to some known factors of IRS adjusting for age, BMI, alcohol use, and smoking. Waist circumference was positively correlated with plasma glucose, DBP, SBP, LDL cholesterol, fasting insulin, serum triglyceride, total cholesterol and total cholesterol/HDL ratio in black and white men and women (P<0.01). In both biracial groups, waist circumference was significantly associated with increases in glucose, DBP, LDL cholesterol, total cholesterol, triglyceride and fasting insulin levels controlling for age, BMI, and behavioral risk factors, such as alcohol use and smoking (P<0.05). Our data shows that central adiposity assessed with waist girth did not wholly explain the higher prevalence of IRS components often seen among blacks. The results of this study reinforce the need to encourage the use of waist measure as a public health tool in screening for CVD risks.
Abdomen↗