Hypertension in a black population: prevalence and biosocial determinants of high blood pressure in a group of urban Nigerians

AIMS

To define the prevalence of hypertension, a major cause of morbidity and mortality in blacks, and related biosocial factors in an urban African population group.

METHODS

The setting was that of a civil service population in Ibadan, a major city in Southwestern Nigeria. Nine hundred and ninety-eight civil servants selected by multistage sampling participated in the survey. Biosocial data including smoking history, alcohol use and level of physical activity; anthropometry, blood pressure and plasma glucose measurements were obtained. Diagnosis of hypertension was based on blood pressure of > or =160/95 mm Hg or known hypertensive on treatment.

RESULTS

The overall prevalence rate of hypertension was 10.3% (CI, 8.4%, 12.2%), rates of 13.9% and 5.3% were obtained in men and women respectively in spite of a much higher rate of generalised obesity in the latter. Hypertension was associated with higher salary grade level, but there was no relationship found with regular exercise, smoking and alcohol. Obesity (body mass index (BMI) > or =30 kg/m2) was associated with hypertension only in women. A two-sided t-test demonstrated age, waist circumference, waist to hip ratio (WHR) and plasma glucose level as significant variables. In multivariate ANOVA models of systolic blood pressures, age, male sex and BMI were highly significant factors (P < 0.0001) and plasma glucose was also significant (P < 0.016); the same variables (except plasma glucose) were associated with diastolic blood pressures. In logistic regression models the variables which predicted hypertension were WHR, plasma glucose, age, sex and family history of diabetes.

CONCLUSIONS

Prevalence of hypertension in the study was comparable to recently reported rates in urban Nigeria and similar populations in Africa. The biosocial determinants of hypertension in the urban black population were age, male gender, higher socio-economic status, BMI, plasma glucose, generalised and central adiposity. Regional fat distribution was a stronger predictor of hypertension than generalised obesity in the population.

Alcohol intake and mortality: findings from the National Health Interview Surveys (1988 and 1990)

The authors used prospective data from two supplemental studies of the National Health Interview Survey, the 1988 Alcohol Supplement and the 1990 Health Promotion and Disease Prevention Supplement, to examine the relation between alcohol intake and mortality. Their study included 17,821 men and 25,874 women aged 40 years or older at baseline; during an average of 6 years of follow-up, 5,540 deaths occurred. The alcohol-mortality relation was U-shaped for men and J-shaped for women. On the basis of categorical analyses adjusted for age, race, smoking, and baseline diseases, men who drank 2 drinks per day had a significantly lower risk of death compared with abstainers (relative risk = 0.60, 95% confidence interval (CI): 0.45, 0.82). The relative risk was 0.75 (95% CI: 0.55, 1.03) after further adjustment for marital status, education, and self-perceived health status. For women, the corresponding relative risks were 0.69 (95% CI: 0.61, 0.78) and 0.79 (95% CI: 0.70, 0.90) for those who drank less than 1 drink per day. When drinking category was considered as an ordinal variable and fitted with a quadratic function in the Cox model, the estimated optimal alcohol intake was approximately less than 1 to 1 drink per day for men and lifetime infrequent to less than 1 drink per day for women. Data from these representative US cohorts demonstrated that less than 2 drinks per day for men and less than 1 drink per day for women are associated with the lowest all-cause mortality.

Predictive values of waist circumference for dyslipidemia, type 2 diabetes and hypertension in overweight White, Black, and Hispanic American adults

Waist circumferences (WC) >/=102 cm for men and >/=88 cm for women have been proposed by an expert panel as cut-points for identifying increased risk for the development of obesity comorbidities for most adults. The aim of this investigation was to examine the predictive values of these WC cut-points for hypercholesterolemia, low concentration of high (HDL-C), and high concentration of low (LDL-C) density lipoprotein cholesterol, hypertriglyceridemia, type 2 diabetes, and hypertension in overweight American adults. Data from NHANES III were utilized for the analysis. Predictive abilities were determined by calculating sensitivity, specificity, positive (PV+) and negative (PV-) predictive values in overweight subjects with BMI 25-29.9 kg/m(2). Sensitivity of WC cut-point was stronger for high LDL-C compared to other risk factors with the highest values recorded in the 40-59 and 60-69 year age groups in men and women, respectively. PV+ of WC cut-points for dyslipidemia, type 2 diabetes, and hypertension were low in men compared to women. PV+ tended to increase with age, from 19-39, 40-59 to 60-90 year age groups in Whites, Blacks, and Hispanic men. In men, the highest PV+ were recorded for hypertriglyceridemia in the 60-90 years old groups, with values of 71.6%, 52.5%, and 43.3% in Whites, Blacks, and Hispanics, respectively. The CVD risk factor associated with the highest PV+ in women was diabetes with values of 97.2% in Whites and 88.9% in Blacks, and hypertriglyceridemia with a value of 93.8% in the 17-39 year age group in Hispanics. Among Black men 40-59 years of age, only 32% of a population of overweight hypertensives were detected by the WC cut-points, and among Black women, 40-59 years of age, only 54% were detected. Given the low sensitivity of these cut-points for detecting hypertension, one of the major co-morbidities of obesity, these cut-points failed to provide adequate evidence for the use of WC in determining or evaluating patients as to co-morbid states. We recommend further studies to determine a set of specific cut-points associated with increased risk of CVD in different population groups.

Impact of birth weight on ethnic variations in subcutaneous and central adiposity in American children aged 5-11 years. A study from the Third National Health and Nutrition Examination Survey

OBJECTIVE

To determine the types of subcutaneous adiposity represented by different measurements of skinfold thickness that are associated with birth weight in white (n=759), Black (n=916) and Hispanic (n=813) American children aged 5-11 y. We also determined the contribution of birth weight to ethnic differences in subcutaneous and central adiposity.

DESIGN AND METHODS

Data for this analysis were from the Third US National Health and Nutrition Examination Survey. The outcome measures were triceps, subscapular, suprailiac and thigh skinfold thicknesses at 5-11 y of age. Central adiposity was defined as ratios of subscapular to triceps (STR) and central-peripheral (CPR) (subscapular+suprailiac)/(triceps+thigh) skinfolds. Partial correlation analyses were used to determine the association between birth weight and measures of subcutaneous fatness, while multiple linear regression analyses were used to determine the independent contribution of birth weight to ethnicity variations in subcutaneous and central adiposity adjusting for sex, age and BMI.

RESULTS

Overall, birth weight was negatively associated with subscapular skinfold and central adiposity in White, Black and Hispanic American children (P < 0.05). Birth weight was also negatively associated with suprailliac skinfold in both Blacks and Hispanics (P < 0.01) and with sum of the four skinfolds in Blacks (P < 0.05). Compared with White, Black ethnicity was negatively associated with triceps, suprailliac thigh and sum of skinfold thicknesses controlling for birth weight, sex, age and BMI (P < 0.01). Compared with White, Hispanic ethnicity was negatively associated with triceps, thigh and sum of skinfold thicknesses (P < 0.01). Both Black and Hispanic ethnicity was positively associated with STR and CPR (P < 0.01).

CONCLUSIONS

In this population of American children, the association of birth weights with subcutaneous and central fat accumulation may be due to fetal programming. Since the impact of fetal conditions is likely to be modified by life course, defining the interaction between factors that are present at birth and subsequent exposures is one of the essential challenges for future research.

Ethnic differences in the rates of low birth weight attributable to differences in early motherhood: a study from the Third National Health and Nutrition Examination Survey

OBJECTIVE

To estimate the impact of early motherhood (being a mother at < 20 years of age) on ethnic differences in the risk of low birth weight (LBW) in a representative sample (n = 9141) of American infants and children.

METHODS

Risks for LBW and the population-attributable fraction due to early motherhood were estimated adjusting for maternal smoking and education in logistic regression models. The contribution of early motherhood to ethnic differences in the risks of LBW was determined using a relative attributable risk estimate that compared Hispanics and Blacks with Whites.

RESULTS

Early motherhood was independently associated with increased risk of LBW in each of the three ethnic groups, adjusting for maternal smoking during pregnancy and education. Hispanic and Black ethnicity were each associated with 15% and 123% increased risk of LBW relative to Whites. The population-attributable fractions of LBW due to early motherhood were 6.2%, 7.4%, and 2.3%, for Whites, Hispanics, and Blacks, respectively. The responses of early motherhood for LBW were different among the three ethnic groups (p < 0.05). Adjusting for maternal smoking and education, 4.8% and 7.4% of the differences in the risk of LBW between Whites and Hispanics and between Whites and Blacks, respectively, were due to differences in early motherhood.

CONCLUSION

The result of this study underscores the risk of LBW due to early motherhood. Because early motherhood is preventable and avoidable, appropriate public health strategies to educate young women on the need to delay childbearing in these ethnic groups, particularly among Hispanics and Blacks, are warranted.

Predictive value of abdominal obesity cut-off points for hypertension in blacks from west African and Caribbean island nations

BACKGROUND

Waist circumferences (WC) >/=94 cm for men and >/=80 cm for women (action level I) and >/=102 cm for men and >/=88 cm for women (action level II) have been suggested as limits for health promotion purposes to alert the general public to the need for weight loss. In this analysis we examined the ability of the above cut-off points to correctly identify subjects with or without hypertension in Nigeria, Cameroon, Jamaica, St Lucia and Barbados. We also determined population- and gender-specific abdominal adiposity cut-off points for epidemiological identification of risk of hypertension.

METHODS

Waist measurement was made at the narrowest part of the torso as seen from the front or at midpoint between the bottom of the rib cage and 2 cm above the top of the iliac crest. Sensitivity and specificity of the established WC cut-off points for hypertension were compared across sites. With receiver operating characteristics (ROC), population- and gender-specific cut-off points associated with risk of hypertension were determined over the entire range of WC values.

RESULTS

Predictive abilities of the established WC cut-off points for hypertension were poor compared to the specific cut-off points estimated for each population. Different values of WC were associated with increased risk of hypertension in these populations. In men, WC cut-off points of 76, 81, 80, 83 and 87 cm provided the highest sensitivity for identifying hypertensives in Nigeria, Cameroon, Jamaica, St Lucia and Barbados, respectively. The analogous cut-off points in women were 72, 82, 85, 86 and 88 cm.

CONCLUSIONS

The waist cut-off points from this study represent values for epidemiological identification of risk of hypertension. For the purpose of health promotion, the decision on what cut-off points to use must be made by considering other additional factors including overall impact on health due to intervention (e.g. weight reduction) and potential burden on health services if a low cut-off point is employed. There is a need to develop abdominal adiposity cut-off points associated with increased risks for cardiovascular diseases in different societies, especially for those populations where the distribution of obesity and associated risk factors tends to be very different from those of the technologically advanced nations. International Journal of Obesity (2000) 24, 180-186

Quality of the last year of life of older adults: 1986 vs 1993

CONTEXT

The population is aging and life expectancy is increasing, but whether morbidity and disability late in life also increase is unknown.

OBJECTIVE

To examine whether the use of health care services, disability and cognitive function, and overall quality of life in the year before death among older adults has changed over time.

DESIGN AND SETTING

The 1986 and 1993 National Mortality Followback Surveys, which were probability samples of all deaths in the United States with response rates of next of kin of 90% and 88% for those aged 65 years and older.

PARTICIPANTS

Next of kin were asked to report the health status of a total of 9179 decedents who were 65 years and older in 1986 and 6735 in 1993, representing 1.5 and 1.6 million decedents aged 65 years and older.

MAIN OUTCOME MEASURES

Days of hospital or nursing home stays, number and length of disability in 5 activities of daily living, duration of impairment in 3 measures of cognitive function, and an overall sickness score among individuals aged 65 through 84 years and those aged 85 years and older.

RESULTS

Women used significantly fewer hospital and nursing home services in the last year of life in 1993 vs 1986 (mean reduction, 3.3 nights for both age groups for hospital services; mean reduction 18.4 nights for nursing home for women aged 65-84 years and 42.3 nights for women > or =85 years). Men had no changes except those aged 85 years and older had a decline in nursing home nights of 32.6. The proportion of women aged 85 years and older with restriction of at least 2 activities of daily living decreased from 62.5% in 1986 to 52.1% in 1993 (P<.01), and those with normal cognitive function increased from 50.3% to 56.2% (P<.05). Their mean overall sickness score decreased and quality-of-life improved. Among women aged 65 through 84 years, the number with normal cognitive function increased and the mean sickness score decreased, but those with at least 2 activities of daily living impairments increased and the overall quality of life declined. A similar pattern of change was found in the oldest-old men except that cognitive function worsened. Most parameters for men aged 65 through 84 years did not change significantly.

CONCLUSIONS

Men and women at least 85 years old in the US experienced a better overall quality of life in the last year of life in 1993 than those in 1986. Most measures for men and women aged 65 through 84 years improved or did not change.

Influence of the I/D polymorphism of the angiotensin-converting enzyme gene on the outcome of microalbuminuria in essential hypertension

The objective of the present study was to analyze the influence of the I/D polymorphism of the ACE gene on the outcome of microalbuminuria in essential hypertensive patients who were receiving antihypertensive treatment. One hundred thirty-six essential hypertensive patients who were <50 years old and had never previously received treatment with antihypertensive drugs were included in the study. During a 3-year period, patients received nonpharmacological treatment consisting of moderate salt restriction and a low-calorie diet they were obese, with or without a regimen of antihypertensive drugs based on beta-blockers or ACE inhibitors. Hydrochlorothiazide was added when necessary to maintain the blood pressure goal of <135/85 mm Hg. At the beginning of the study and at yearly intervals, systolic and diastolic blood pressures (SBP and DBP, respectively), 24-hour urinary albumin excretion (UAE), renal function, and biochemical profile measurements were made. The insertion/deletion (I/D) polymorphism of the ACE gene was determined through the use of polymerase chain reaction. The variables used in the statistical analysis were the measurements at the start of the study and the increase or decrease detected during the follow-up, estimated as individual specific regression line slope values. At baseline, no differences in blood pressure or UAE values were observed among genotypes. Likewise, the genotype or allele frequency was not significantly different between normoalbuminurics and microalbuminurics. After the 3 treatment years, significant reductions in SBP, DBP, and UAE were found (SBP 151.6+/-17.3 reduced to 137.2+/-14.3 mm Hg, P<0.001; DBP 96.6+/-8.9 reduced to 84.5+/-9.8 mm Hg, P<0.001; UAE 36.7+/-71.5 reduced to 28.3+/-78.6 mg/24 h, P<0. 05). The slopes of these parameters over time did not differ significantly among genotypes. The slope of SBP was the main factor related to the slope of logUAE (P<0.003). A significant positive correlation coefficient between the SBP and logUAE slopes was observed for the DD patients (r=0.57, P<0.0001) but was absent in patients carrying the I allele (II r=-0.03, P=NS; I/D r=0.01, P=NS). Follow-up studies should be used to achieve a better understanding of the impact of candidate gene polymorphisms on the development of hypertension-induced organ damage. Assessment of the I/D polymorphism of the ACE gene may identify subjects who require a greatly lowered blood pressure to prevent organ damage and to reduce hypertension-associated complications and death.

Mortality among US adult Asians and Pacific Islanders: findings from the National Health Interview Surveys and the National Longitudinal Mortality Study

OBJECTIVES

To assess the mortality of the adult Asian and Pacific Islander population in the United States.

METHODS

Cohort study using data from the National Health Interview Survey (1986 to 1994) and the National Longitudinal Mortality Study. Deaths were ascertained by matching the National Death Index with average follow-ups of 5.3 and 9 years, respectively, for the two studies.

RESULTS

Respondents from the pooled National Health Interview Surveys included 532,794 non-Hispanic whites, 94,242 blacks, 52,725 Hispanics, and 16,936 Asians and Pacific Islanders, all of whom were at least 18 years of age at baseline. The National Longitudinal Mortality Study included 373,397 non-Hispanic whites, 41,262 blacks, 23,356 Hispanics, and 8,390 Asians and Pacific Islanders. Overall age-standardized mortality was the lowest in Asians/Pacific Islanders, whose risk of death was about 40% lower than whites'. Adjustment for differences in education levels had a minimal influence on the mortality advantage in Asians/Pacific Islanders.

CONCLUSIONS

Longitudinal cohorts provide an important source of health status information on Asians and Pacific Islanders. These two studies from representative national samples suggest that overall mortality is substantially lower among Asians and Pacific Islanders than in all other major ethnic groups.

Diabetes in the Caribbean: results of a population survey from Spanish Town, Jamaica

AIMS

To characterize the prevalence of diabetes and associated risk attributes in the Jamaican population.

METHODS

A random population sample was recruited by door-to-door canvassing (n = 1303). A final participation of 60% was achieved. Oral glucose tolerance testing was conducted after an overnight fast and standard anthropometric and demographic data were collected.

RESULTS

The prevalence of Type 2 diabetes mellitus was 9.8% (95% confidence interval (CI) 7.2-12.4) among men and 15.7% (95% CI 13.1-18.3) among women with an overall prevalence of 13.4% (95% CI 11.5-15.2). Impaired glucose tolerance was found among 12.3% of men and 14.7% of women. The sex patterns were consistent with a fourfold excess of obesity in women compared to men. The odds ratios for diabetes, fourth vs. first quartiles were 5.42 (95% CI 2.02-16.88) in men and 3.32 (95% CI 1.73-6.63) in women for body mass index (BMI) and 17.39 (95% CI 3.86-78.27) in men and 5.48 (95% CI 2.84-11.00) in women for WHR in a logistic model controlling for age. The population attributes risk percentage, for diabetes, of being overweight and having waist-to-hip ratio (WHR) greater than the median (0.80) were 66% and 80%, respectively. The contribution of central obesity, as characterized by WHR, was also significant in sex-specific multivariate models that included age and BMI. Prevalent hypertension and family history of diabetes were likewise associated with increased odds of having the disease.

CONCLUSIONS

The prevalence of diabetes in Jamaica now exceeds that observed among European-origin populations and reflects the emerging epidemic of obesity. The excess risk for this population could not be attributed entirely to relative weight. The pronounced sexual dimorphism in diabetes prevalence most likely reflects the substantial excess of obesity among women compared to men. Like many other island nations, Caribbean societies now appear to be at substantial risk of diabetes.

Genetic and physiologic analysis of the role of uncoupling protein 3 in human energy homeostasis

By virtue of its potential effects on rates of energy expenditure, uncoupling protein 3 (UCP3) is an obesity candidate gene. We identified nine sequence variants in UCP3, including Val9Met, Val102Ile, Arg282Cys, and a splice site mutation in the intron between exons 6 and 7. The splice mutation results in an inability to synthesize mRNA for the long isoform (UCP3L) of UCP3. Linkage (sib pair), association, and transmission disequilibrium testing studies on 942 African-Americans did not suggest a significant effect of UCP3 on body composition in this group. In vastus lateralis skeletal muscle of individuals homozygous for the splice mutation, no UCP3L mRNA was detectable; the short isoform (UCP3S) was present in an increased amount. In this muscle, we detected no alterations of in vitro mitochondrial coupling activity, mitochondrial respiratory enzyme activity, or systemic oxygen consumption or respiratory quotient at rest or during exercise. These genetic and physiologic data suggest the following possibilities: UCP3S has uncoupling capabilities equivalent to UCP3L; other UCPs may compensate for a deficiency of bioactive UCP3L; UCP3L does not function primarily as a mitochondrial uncoupling protein.

Abdominal adiposity in six populations of West African descent: prevalence and population attributable fraction of hypertension

OBJECTIVES

The objective of this investigation was to examine the prevalence of abdominal adiposity and its association with the prevalence of hypertension among African descent populations in Nigeria, Cameroon, Jamaica, St. Lucia, Barbados, and the United States (US).

RESEARCH METHOD

The data for this investigation were obtained from the International Collaborative Study on Hypertension in Blacks. Hypertension was defined as mean diastolic blood pressure > or =90 mmHg, systolic blood pressure > or = 140 mmHg or current treatment with prescribed anti-hypertension medication. Abdominal overweight was defined as waist circumference (WC) > or =94 and > or =80 cm for men and women, respectively. Abdominal obesity was defined as WC > or =102 and > or =88 cm for men and women, respectively. We estimated the site-specific prevalence of abdominal overweight and obesity across age and body mass index cut-points. We also calculated the population attributable fraction (AF) of hypertension due to abdominal adiposity.

RESULTS

The prevalence of hypertension in these populations was tightly linked to abdominal adiposity. Increases in abdominal overweight accompanied an increasing degree of Westernization, rising from 6.4% and 26.3% in Nigeria, 16.5% and 62.8% in Cameroon, 15.8% and 58.6% in Jamaica, 14.3% and 62.1% in St. Lucia, 21.4% and 70.3% in Barbados to 38.9%, and 76.4% in the US for men and women, respectively. The corresponding values for abdominal obesity were 1.6% and 12.3% in Nigeria, 5.1% and 38.9% in Cameroon, 5.5% and 34.0% in Jamaica, 2.7% and 40.7% in St. Lucia, 7.8% and 44.7% in Barbados to 21.7% and 54.1% in the US for men and women, respectively. Body mass index-adjusted estimates of AF suggest that in most of these populations, especially in females, avoidance of abdominal overweight or obesity would help to curb the development of hypertension.

DISCUSSION

An important public health challenge is to clarify how lifestyle factors influence risks of abdominal adiposity and ultimately the increased risk of cardiovascular diseases.

Evidence for the involvement of JAK/STAT pathway in the signaling mechanism of interleukin-17

Interleukin-17 is a T-cell-derived pro-inflammatory cytokine, exhibiting multiple biological activities in a variety of cells and believed to fine tune all general phases of hematopoietic response. However, the signaling mechanism of this novel cytokine remains unknown. Here, we report for the first time that the early signaling events triggered by interleukin-17 involve tyrosine phosphorylation of several members of the JAK and STAT proteins in human U937 monocytic leukemia cells. Immunoprecipitation with specific antibodies followed by Western blot analysis with antiphosphotyrosine antibody has shown that in U937 cells, interleukin-17 induces time-dependent stimulation of tyrosine phosphorylation of JAK 1, 2 and 3, Tyk 2 and STAT 1, 2, 3 and 4 within 0.5 to 30 min. Interleukin-17-mediated tyrosine phosphorylation of these proteins strongly suggests that the JAK/STAT signaling pathway may play a major role in transducing signals from interleukin-17 receptors to the nucleus.

Blood pressure change in Africa: case study from Nigeria

Studies of migrants and comparisons of rural versus urban communities are potentially informative study designs because they allow examination of genetically similar population subgroups exposed to diverse environmental conditions. These designs have been underused in Africa, where recent urbanization has created many situations in which nearby communities of common ethnicity and culture live under different social and economic circumstances. The International Study of Hypertension in Blacks (ICSHIB) conducted several overlapping surveys in Nigeria starting in 1993. These surveys were based primarily in the rural village of Idere and the urban community of Idikan, both inhabited by people defined ethnically as Oyo Yoruba and sharing a common language and culture. Survey teams collected standardized blood pressure and anthropometric measurements, and some study participants provided 24-hr urine samples and questionnaire data on psychosocial stress and social integration. Rural and urban groups differed substantially in blood pressure and related characteristics. Age-adjusted prevalence of hypertension (blood pressure > or = 140/90 mm Hg) for participants aged 25 years and older was 7-8% in Idere and 24-27% in Idikan. The distributions of overweight, sodium/potassium ratio, perceived stress, and social integration scores all contributed to lower hypertension risk in Idere. The effects and interactions of these identified risk factors remain poorly understood, even among people who share a common genetic background, similar diet, and many other lifestyle features. Nonetheless, the rural-urban distinction is sufficiently salient to engender a nearly threefold difference in hypertension prevalence. This disparity in disease prevalence demonstrates the sensitivity of human beings to the environmental determinants of disease and provides a sobering example of the difficulty in identifying subtle genetic effects, which can be easily overwhelmed by small differences in environmental exposures.

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.

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.

Seeking causal explanations in social epidemiology

Social factors are associated with a wide variety of health outcomes. Social epidemiology has successfully used the traditional methods of surveillance and description to establish consistent relations between social factors and health status. Epidemiology as an etiologic science, however, has been largely ineffective in moving toward causal explanations for these observed patterns. Using the counterfactual approach to causal inference, the authors describe several fundamental problems that often arise when researchers seek to infer explanatory mechanisms from data on social factors. Contrasts that form standard causal effect estimates require implicit unobserved (counterfactual) quantities, because observational data provide only one exposure state for each individual. Although application of counterfactual arguments has successfully advanced etiologic understanding in other observational settings, the particular nature of social factors often leads to logical contradictions or misleading inferences when investigators fail to clearly articulate the counterfactual contrasts that are implied. For example, because social factors are often attributes of individuals and are components of structured social relations, random assignment is not plausible even as a hypothetical experiment, making typical epidemiologic contrasts inappropriate and the inference equivocal at best. Accordingly, more deliberate and creative approaches to causal inference in social epidemiology are required. Infectious disease epidemiology and systems analysis provide examples of approaches to causal inference that can be used when statistical mimicry of simple experimental designs is not tenable. In an era of increasing social inequality, valid approaches for the study of social factors and health are needed more urgently than ever.

Abdominal obesity in the United States: prevalence and attributable risk of hypertension

OBJECTIVE

The aim of this study was to determine the prevalence of abdominal obesity and its impact on the risks of hypertension in the US adult population.

DESIGN AND METHODS

Data from the third US National Health and Nutrition Examination Surveys, 1988-1994, were utilised. Abdominal obesity was defined as waist circumference > or =102 cm in men and > or =88 cm in women. Hypertension was defined as mean diastolic blood pressure > or =90 mm Hg, systolic blood pressure > or =140 mm Hg or current treatment with prescribed hypertension medication. Prevalences of abdominal obesity were estimated in non-Hispanic White, non-Hispanic Black and Hispanic Americans. Gender-specific logistic regression analysis using empirical waist cut-off points was used to determine the risks of hypertension. The impact of abdominal adiposity on risk of hypertension was estimated from population-attributable risk adjusting for age, current smoking and alcohol intake.

RESULTS

The prevalences of abdominal obesity were 27.1%, 20.2% and 21.4% in White, Black and Hispanic men, respectively. The corresponding values in women were 43.2%, 56.0% and 55.4%. Abdominal obesity was found to be associated with a two to three-fold increased risk of hypertension in this population. In men, the attributable risk percent ranged from 20.9% in Hispanics to 27.3% in Whites and in women ranged from 36.5% in Whites to 56.5% in Hispanics. We estimated that 24 million adult men and 40 million adult women of Hispanic and non-Hispanic Black and White ethnicity were suffering from abdominal obesity.

CONCLUSIONS

In this population, hypertension appears to be associated with abdominal obesity. The estimates of population attributable risks suggest that the risk of hypertension could be potentially reduced if waist size were reduced to <102 cm in men and <88 cm in women.

Limitations in the use of race in the study of disease causation

Tremendous variation exists in the rates of many chronic diseases across racial groups. However, serious technical and conceptual limitations hamper the ability of racial comparisons to illuminate the causative pathways. First, race is confounded by social class, which is complex, and like other confounders of race, may not be measured with equal validity across racial groups. Second, statistical "adjustments" for race effects can be misleading since residual confounding may be misconstrued as a genetic effect. Third, the biologic concept of race tempts us to ignore the context dependency of genetic expression. When trying to detect genetic effects, both the environmental and genetic contributions must be measured and potential gene-environment interactions accounted for. Unfortunately, this process is beyond our current technical capabilities. To move forward on the problem of prostate cancer and other diseases distinguished by marked ethnic differentials, investigators need a more comprehensive understanding of the factors that mediate the apparent effect of race combined with valid measures of those factors, as well as novel strategies that can help overcome the technical and interpretive limitations of statistical adjustment. Finally, the "grand" theories of race-based genetic susceptibility must be replaced with rigorous criteria to determine when a trait can be ascribed to some genetic origin.

Prediction of coronary heart disease mortality in blacks and whites: pooled data from two national cohorts

Statistical models used to predict personal risk of death from coronary heart disease (CHD) have been based on studies among white populations. We compared the predictive functions derived from black and white men and women, using the pooled data of 2 national cohorts: the First National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Follow-up Study and the Second National Health and Nutrition Examination Survey (NHANES II) Mortality Study. The participants included 6,937 white men, 940 black men, 9,202 white women, and 1,463 black women aged 30 to 74 years who were free of CHD at baseline. The 2 cohorts were followed for 20 and 15 years, respectively. There were no significant differences between blacks and whites in the magnitude of the Cox coefficients for most of the personal risk factors (i.e., age, systolic blood pressure, serum total cholesterol, smoking, and diabetes mellitus status) for men and women. The receiver operating characteristic (ROC) analyses, with all risk factors considered collectively, suggest that the models have similar ability to rank personal relative risk among blacks and whites. The areas under the ROC curve were 0.77 and 0.76 for white and black men, respectively, and 0.84 and 0.82 for white and black women, respectively. However, the equation derived from white men overestimated the 15-year cumulative CHD mortality in black men by about 60%. Thus, predictive functions derived from 1 demographic group (e.g., whites) can be applied to another subgroup (e.g., blacks) to rank personal risk. However, prediction of absolute risk is less accurate.

Black-white differences in disability and morbidity in the last years of life

To assess black-white differences in disability and morbidity in the last years of life, the authors analyzed data from the National Health Interview Survey from 1986 to 1994, with mortality follow-up through December 1995. A baseline household interview was conducted for 10,187 decedents aged 50 years and over within 2 years before death. Data collected included long-term limitation of activity, number of chronic conditions, number of bed days, doctor visits, and days of short hospital stay during the year preceding the interview. For both blacks and whites, educational attainment was inversely associated with disability/morbidity indices. Black decedents had greater morbidity compared with whites, and this difference was consistent across educational levels. Adjustment for education reduced the black-white difference in limitation of activity score by 32%, bed days by 59%, and hospital stay days by 40%. This study from a national representative US sample indicates that black decedents experienced greater disability/morbidity and worse quality of life through their last few months or years of life. Educational attainment was associated with morbidity before death and accounted for much of the black-white difference.

The long isoform uncoupling protein-3 (UCP3L) in human energy homeostasis

The biological role(s) proposed for UCP3 in energy homeostasis have been based primarily upon amino acid sequence homology to UCP1. Spontaneous mutations of UCP3> have been described in humans, but not in rodents. The functional consequences-or lack thereof-of these mutations in humans will be of great importance in elucidating the biology of this protein. The results of two such studies are summarized here.

How generalizable are coronary risk prediction models? Comparison of Framingham and two national cohorts

BACKGROUND

Previous models used to predict individual risk of death from coronary heart disease (CHD) were developed from data of 3 decades ago from the Framingham Heart Study. CHD mortality rates have declined markedly since that period as a result of improvement in both risk factor status and medical interventions. Generalization of the results from this one study to the population at large remains a matter of concern. We compared predictive functions derived from the major risk factors for CHD from Framingham and 2 more recent national cohorts, the First and Second National Health and Nutrition Examination Survey (NHANES I and NHANES II).

METHODS AND RESULTS

The participants included 1846 men and 2323 women 35 to 69 years of age and free of CHD at the fourth examination (1954 to 1958) from the Framingham Study; 2753 men and 3858 women from the NHANES I (1971 to 1975); and 2655 men and 3050 women from NHANES II (1976 to 1980). The 3 cohorts were monitored for 24, 20, and 15 years, respectively. Significant heterogeneity existed among studies in the magnitude of the Cox coefficients for the individual factors (ie, age, systolic blood pressure, serum total cholesterol, and smoking status), especially among men. When risk factors were considered collectively, however, functions derived from and applied to different cohorts had a similar ability to rank individual risk. The areas under the receiver operating characteristic curves were 0. 71 to 0.76 in men and 0.76 to 0.81 in women when different risk functions were applied to their own population or to a second population. The cumulative CHD survival observed in women in the 2 national cohorts was close to what was predicted from the Framingham equation. However, Framingham overestimated the cumulative CHD mortality rates in men in NHANES I and NHANES II.

CONCLUSIONS

The Framingham risk model for the prediction of CHD mortality rates provides a reasonable rank ordering of risk for individuals in the US white population for the period 1975 to 1990. However, prediction of absolute risk is less accurate.