Abstract
We analyzed cardiovascular disease mortality risks associated with obesity using participant-level meta-analysis of data from the Black Pooling Project for Black and White individuals. The adjusted relative risks (ARRs) were stronger among White participants than among Black participants for coronary heart disease AAR=1.21 (95% confidence interval [CI]=1.07, 1.36) versus 0.87 (95% CI=0.69, 1.09), respectively, and cardiovascular disease ARR=1.18 (95% CI=1.07, 1.29) versus 0.91 (95% CI=0.77, 1.05), repectively. The results suggest that obesity is an independent risk factor in White people, and additional study of body size and disease progression is necessary in the assessment of racial disparities.
Increased body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) has been associated with increased risks for cardiovascular disease.1–4 Likewise, the racial disparities in obesity, cardiovascular disease, and stroke have left Black patients with a particularly heavy disease burden.5–7 However, the disease risks attributed to obesity are inconsistent and less clear for Black individuals than for White individuals.1,3,4,8–22 The association between obesity and cardiovascular disease is limited because of the relative paucity of long-term follow-up outcomes for Black men and women. We examined the association between BMI and coronary heart disease (CHD), stroke, and cardiovascular disease mortality by reviewing data from the Black Pooling Project, which includes more than 450 000 person-years of follow-up.
METHODS
Data Source
The Black Pooling Project includes participant-level data on 27691 persons (4853 Black and 22 838 White) from 4 studies: Evans County Heart Study, Charleston Heart Study, and National Health and Nutrition Examination Survey I and II (NHANES I and II). Baseline values, collected between 1960 and 1980, included height, weight, blood pressure, cholesterol, diabetes status, and smoking status.23–27 Mortality follow-up ranged from 15 to 30 years and included more than 450 000 person-years (82 893 Black and 368069 White).
Analysis
We used 3 Cox proportional hazards regression models to calculate the relative risk of CHD, stroke, and cardiovascular disease mortality associated with obesity (BMI ≥ 30 kg/m2), with normal weight (BMI = 18.5–24.9 kg/m2) as the referent group. The covariates in each of these models were chosen a priori. Model 1 was adjusted for age; model 2 for age and smoking status; and model 3 for age, smoking status, hypertension, cholesterol, and diabetes. We ran these models for each race group (Black and White) and each gender in both race groups (Black and White men and women) separately in each of the 4 cohorts and then pooled them according to participant-level meta-analysis to obtain an overall estimate. We tested the racial differences in the association between obesity and mortality with a z statistic—calculated as the difference in the estimated regression coefficients for obesity in Black and White individuals divided by the standard error of the difference.
RESULTS
Table 1 ▶ presents descriptive characteristics of participants in the Black Pooling Project.
TABLE 1—
Sample Characteristics for Black and White Women and Men: Black Pooling Project
| Black | White | |||||
| Total | Women | Men | Total | Women | Men | |
| Total sample, No. | 4853 | 2843 | 2010 | 22 838 | 12 739 | 10 099 |
| Deaths, No. (%) | ||||||
| Cardiovascular disease deaths | 1165 (24) | 636 (22) | 529 (26) | 3738 (16) | 1654 (13) | 2084 (21) |
| Coronary heart disease deaths | 569 (12) | 297 (10) | 272 (14) | 2388 (10) | 980 (8) | 1408 (14) |
| Stroke deaths | 302 (6) | 174 (6) | 128 (6) | 631 (3) | 343 (3) | 288 (3) |
| Person-years | 82 893 | 50 881 | 32 012 | 368 069 | 215 400 | 152 669 |
| Age, y, mean (SD) | 51.1 (14) | 50.1 (14) | 52.7 (14) | 51.3 (14) | 50.4 (15) | 52.4 (14) |
| Blood pressure, mm Hg, mean (SD) | ||||||
| Systolic blood pressure | 148 (32) | 149 (34) | 147 (29) | 134 (23) | 133 (25) | 136 (21) |
| Diastolic blood pressure | 91 (16) | 90 (16) | 92 (16) | 83 (12) | 82 (12) | 85 (12) |
| Cholesterol, mg/dL, mean (SD) | 220 (48) | 223 (49) | 216 (46) | 224 (48) | 227 (51) | 221 (45) |
| BMI,a % | ||||||
| Underweight | 4 | 5 | 4 | 4 | 4 | 3 |
| Normal weight | 38 | 31 | 48 | 47 | 51 | 42 |
| Overweight | 32 | 31 | 34 | 34 | 27 | 43 |
| Obese | 17 | 21 | 11 | 11 | 12 | 11 |
| Morbidly obese | 9 | 13 | 3 | 4 | 6 | 2 |
| Diabetes, % | 6 | 7 | 5 | 4 | 4 | 4 |
| Smoking status, % | ||||||
| Nonsmoker | 54 | 66 | 36 | 46 | 59 | 29 |
| Former smoker | 9 | 6 | 13 | 21 | 13 | 31 |
| Current smoker | 37 | 28 | 51 | 33 | 28 | 40 |
aBMI = body mass index; weight in kilograms divided by height in meters squared, Underweight was defined as <18.5 kg/m2, normal weight as 18.5–24.9 kg/m2, overweight as 25–29.9 kg/m2, obese as 30–34.9 kg/m2, and morbidly obese as ≥ 35 kg/m2.
Among White persons, obesity was independently associated with CHD, stroke, and cardiovascular disease mortality in models 1 and 2 and with CHD and cardiovascular disease mortality in model 3 (Table 2 ▶). In model 2, which controlled for age and smoking, obesity had a significantly stronger association with CHD (P = .002), stroke (P = .012), and cardiovascular disease (P < .001) mortality among White individuals than among Black individuals. Similar results were obtained when the association between obesity and CHD, stroke, and cardiovascular disease mortality was calculated for each gender–race group.
TABLE 2—
Relative Risk (RRs) and 95% Confidence Intervals (CIs) of Coronary Heart Disease (CHD), Stroke, and Total Cardiovascular Disease Mortality Associated With Obesity Among Black and White Men and Women: Black Pooling Project
| CHD, RR (95% CI) | Stroke, RR (95% CI) | Cardiovascular Disease, RR (95% CI) | |
| Total population | |||
| Model 1 | |||
| Blacks | 1.12 (0.91, 1.38) | 0.81 (0.61, 1.09) | 0.97 (0.84, 1.12) |
| Whites | 1.33a (1.19, 1.48) | 1.33a (1.08, 1.65) | 1.34a (1.22, 1.46) |
| Model 2 | |||
| Blacks | 1.01 (0.81, 1.26) | 0.84 (0.63, 1.13) | 1.02 (0.88, 1.20) |
| Whites | 1.50a (1.34, 1.69) | 1.40a (1.12, 1.73) | 1.48a (1.35, 1.62) |
| Model 3 | |||
| Blacks | 0.87 (0.69, 1.09) | 0.84 (0.61, 1.16) | 0.91 (0.77, 1.05) |
| Whites | 1.21a (1.07, 1.36) | 1.14 (0.91, 1.44) | 1.18a (1.07, 1.29) |
| Women | |||
| Model 1 | |||
| Blacks | 1.21 (0.90, 1.61) | 0.98 (0.68, 1.43) | 1.12 (0.93, 1.36) |
| Whites | 1.55a (1.32, 1.81) | 1.37a (1.04, 1.81) | 1.52a (1.34, 1.72) |
| Model 2 | |||
| Blacks | 1.18 (0.88, 1.60) | 1.08 (0.73, 1.60) | 1.14 (0.94, 1.39) |
| Whites | 1.67a (1.42, 1.97) | 1.42a (1.07, 1.60) | 1.61a (1.42, 1.82) |
| Model 3 | |||
| Blacks | 1.03 (0.76, 1.42) | 0.96 (0.64, 1.45) | 1.02 (0.83, 1.25) |
| Whites | 1.32a (1.12, 1.57) | 1.15 (0.85, 1.54) | 1.27a (1.12, 1.45) |
| Men | |||
| Model 1 | |||
| Blacks | 0.94 (0.65, 1.34) | 0.73 (0.40, 1.33) | 0.96 (0.74, 1.24) |
| Whites | 1.32a (1.12, 1.54) | 1.46a (1.04, 2.07) | 1.32a (1.16, 1.51) |
| Model 2 | |||
| Blacks | 0.96 (0.65, 1.40) | 0.74 (0.39, 1.40) | 0.99 (0.76, 1.31) |
| Whites | 1.43a (1.21, 1.69) | 1.50a (1.05, 2.14) | 1.42a (1.24, 1.63) |
| Model 3 | |||
| Blacks | 0.86 (0.57, 1.28) | 0.65 (0.34, 1.25) | 0.88 (0.66, 1.17) |
| Whites | 1.18a (1.00, 1.41) | 1.23 (0.85, 1.78) | 1.16a (1.01, 1.34) |
Note. Model 1 was adjusted for age. Model 2 was adjusted for age and smoking status. Model 3 was adjusted for age, smoking status, cholesterol, diabetes, and hypertension. Obese was defined as having a body mass index (weight in kilograms divided by height in meters squared) as 30.0–34.9 kg/m2.
aP = .05.
Given that a previous report suggested that cardiovascular disease risk begins at a higher BMI for Black than for White individuals,21,28 we also examined risk associated with morbid obesity (BMI ≥ 35 kg/m2). Among Black individuals, morbid obesity was not independently associated with cardiovascular disease mortality (relative risk [RR] = 1.09; 95% confidence interval [CI] = 0.89, 1.36), whereas among White individuals, the risk of cardiovascular disease mortality increased further (RR = 1.51; 95% CI = 1.29, 1.76).
DISCUSSION
Although significant differences in body size and cardiovascular disease mortality have been confirmed between Black and White persons, the association between obesity and mortality remains inconsistent. The Black Pooling Project enhanced the findings of previous studies that suggested that the risk of death associated with a high BMI is stronger among White than among Black people1,12 by identifying a significantly greater association between obesity and CHD, stroke, and cardiovascular disease mortality among White individuals. Among White participants, obesity was independently associated with CHD, stroke, and cardiovascular disease mortality after adjustment for age and for age and smoking, and with CHD and cardiovascular disease mortality after adjustment for multiple comorbid risk factors. The association between obesity and stroke among White participants was attenuated in the fully adjusted model; however, the association remained significant when hypertension was removed from the model.
These results were limited by several factors, including the lack of data on body fat pattern, particularly measures of waist circumference and abdominal visceral fat, which have been shown to be strongly associated with cardiovascular disease mortality.14,29,30 This study was also limited by the use of only baseline measures for BMI and other covariates. This analysis was limited to CHD, stroke, and cardiovascular disease mortality and did not consider competing causes of mortality.
These findings confirm a stronger association between BMI and CHD, stroke, and cardiovascular disease mortality among White than among Black individuals. Nonetheless, obesity should be considered a significant risk factor for both Black and White people, and weight loss and management strategies should be used to reduce the racial disparities in cardiovascular disease. Clearly, comorbid conditions, including hypertension and diabetes, are strongly associated with obesity and have significant racial differences in severity and prevalence. Nonetheless, our results suggested that obesity does not explain the racial disparities in CHD, stroke, and cardiovascular disease. Additional longitudinal studies are needed to investigate the mechanisms of obesity and cardiovascular disease progression as well as the risks attributed to race in disease outcomes. Likewise, the results of this long-term follow-up study support the implementation of public health intervention strategies targeting all segments of the population.
Acknowledgments
This work was supported by a predoctoral fellowship from the American Heart Association. The Black Pooling Project was funded by the National Institutes of Health (grant 1R01HL072377).
Note. All analyses, interpretations, and conclusions based on data from the National Center for Health Statistics were made by the authors only.
Human Participant Protection This study was approved by the Medical University of South Carolina institutional review board.
Peer reviewed
Contributors J. E. Abell developed the data analysis plan, performed all data analysis, and drafted and reviewed the brief. B. M. Egan assisted with the interpretation of the data and writing of the brief. P.W.F. Wilson assisted with the interpretation of the data. R. F. Woolson and S. Lipsitz provided statistical expertise. D. T. Lackland assisted with study origination and interpretation of the data.
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