Samson Y. Gebreab

A Review of Spatial Methods in Epidemiology, 2000–2010

Understanding the impact of place on health is a key element of epidemiologic investigation, and numerous tools are being employed for analysis of spatial health-related data. This review documents the huge growth in spatial epidemiology, summarizes the tools that have been employed, and provides in-depth discussion of several methods. Relevant research articles for 2000-2010 from seven epidemiology journals were included if the study utilized a spatial analysis method in primary analysis (n = 207). Results summarized frequency of spatial methods and substantive focus; graphs explored trends over time. The most common spatial methods were distance calculations, spatial aggregation, clustering, spatial smoothing and interpolation, and spatial regression. Proximity measures were predominant and were applied primarily to air quality and climate science and resource access studies. The review concludes by noting emerging areas that are likely to be important to future spatial analysis in public health.

Perceived Discrimination and Hypertension Among African Americans in the Jackson Heart Study

OBJECTIVES Using Jackson Heart Study data, we examined whether perceived discrimination was associated with prevalent hypertension in African Americans. METHODS Everyday discrimination, lifetime discrimination, burden of discrimination, and stress from discrimination were examined among 4939 participants aged 35 to 84 years (women = 3123; men = 1816). We estimated prevalence ratios of hypertension by discrimination, and adjusted for age, gender, socioeconomic status, and risk factors. RESULTS The prevalence of hypertension was 64.0% in women and 59.7% in men. After adjustment for age, gender, and socioeconomic status, lifetime discrimination and burden of discrimination were associated with greater hypertension prevalence (prevalence ratios for highest vs lowest quartile were 1.08 [95% confidence interval (CI) = 1.02, 1.15] and 1.09 [95% CI = 1.02,1.16] for lifetime discrimination and burden of discrimination, respectively). Associations were slightly weakened after adjustment for body mass index and behavioral factors. No associations were observed for everyday discrimination. CONCLUSIONS Further understanding the role of perceived discrimination in the etiology of hypertension may be beneficial in eliminating hypertension disparities.

The socioeconomic gradient of diabetes prevalence, awareness, treatment, and control among African Americans in the Jackson Heart Study.

PURPOSE Little research has focused on the social patterning of diabetes among African Americans. We examined the relationship between socioeconomic status (SES) and the prevalence, awareness, treatment, and control of diabetes among African Americans. METHODS Education, income and occupation were examined among 4,303 participants (2,726 women and 1,577 men). Poisson regression estimated relative probabilities (RP) of diabetes outcomes by SES. RESULTS The prevalence of diabetes was 19.6% in women and 15.9% in men. Diabetes awareness, treatment, and control were 90.0%, 86.8%, and 39.2% in women, respectively, and 88.2%, 84.4%, and 35.9% in men, respectively. In adjusted models, low-income men and women had greater probabilities of diabetes than high-income men and women (RP, 1.94; 95% confidence interval [CI], 1.28-2.92; and RP, 1.35; 95% CI, 1.04-1.74, respectively). Lack of awareness was associated with low education and low occupation in women (RP, 2.28; 95%CI 1.01-5.18; and RP, 2.62; 95% CI, 1.08-6.33, respectively) but not in men. Lack of treatment was associated with low education in women. Diabetes control was not patterned by SES. CONCLUSIONS Diabetes prevalence is patterned by SES, and awareness and treatment are patterned by SES in women but not men. Efforts to prevent diabetes in African Americans need to address the factors that place those of low SES at higher risk.

The Contribution of Stress to the Social Patterning of Clinical and Subclinical CVD Risk Factors in African Americans: The Jackson Heart Study

It is often hypothesized that psychosocial stress may contribute to associations of socioeconomic position (SEP) with risk factors for cardiovascular disease (CVD). However, few studies have investigated this hypothesis among African Americans, who may be more frequently exposed to stressors due to social and economic circumstances. Cross-sectional data from the Jackson Heart Study (JHS), a large population-based cohort of African Americans, were used to examine the contributions of stressors to the association of SEP with selected cardiovascular (CVD) risk factors and subclinical atherosclerotic disease. Among women, higher income was associated with lower prevalence of hypertension, obesity, diabetes and carotid plaque and lower levels of stress. Higher stress levels were also weakly, albeit positively, associated with hypertension, diabetes, and obesity, but not with plaque. Adjustment for the stress measures reduced the associations of income with hypertension, diabetes and obesity by a small amount that was comparable to, or larger, than the reduction observed after adjustment for behavioral risk factors. In men, high income was associated with lower prevalence of diabetes and stressors were not consistently associated with any of the outcomes examined. Overall, modest mediation effects of stressors were observed for diabetes (15.9%), hypertension (9.7%), and obesity (5.1%) among women but only results for diabetes were statistically significant. No mediation effects of stressors were observed in men. Our results suggest that stressors may partially contribute to associations of SEP with diabetes and possibly hypertension and obesity in African American women. Further research with appropriate study designs and data is needed to understand the dynamic and interacting effects of stressors and behaviors on CVD outcomes as well as sex differences in these effects.

Exploring racial disparities in CHD mortality between blacks and whites across the United States: a geographically weighted regression approach.

Coronary heart disease (CHD) mortality is one of the major contributors to racial disparities in health in the United States (US). We examined spatial heterogeneity in black-white differences in CHD mortality across the US and assessed the contributions of poverty and segregation. We used county-level, age-adjusted CHD mortality rates for blacks and whites in the continental US between 1996 and 2006. Geographically weighted regression was employed to assess spatial heterogeneity. There was significant spatial heterogeneity in black-white differences in CHD mortality (median black-white difference 17.7 per 100,000, 25th-75th percentile (IQR): 4.0, 34.0, P value for spatial non-stationarity <0.0001) before controlling for poverty and segregation. This heterogeneity was no longer present after accounting for county differences in race-specific poverty and segregation and interactions of these variables with race (median black-white difference -13.5 per 100,000, IQR: -41.3, 15.7,P value for spatial non-stationarity=0.4346). The results demonstrate the importance of spatial heterogeneity in understanding and eliminating racial disparities in CHD mortality. Additional research to identify the individual and contextual factors that explain the local variations in racial disparities is warranted.

Geographic Variations in Cardiovascular Health in the United States: Contributions of State‐ and Individual‐Level Factors

Background Improving cardiovascular health (CVH) of all Americans by 2020 is a strategic goal of the American Heart Association. Understanding the sources of variation and identifying contextual factors associated with poor CVH may suggest important avenues for prevention. Methods and Results Cross-sectional data from the Behavioral Risk Factor Surveillance System for the year 2011 were linked to state-level coronary heart disease and stroke mortality data from the National Vital Statistics System and to state-level measures of median household income, income inequality, taxes on soda drinks and cigarettes, and food and physical activity environments from various administrative sources. Poor CVH was defined according to the American Heart Association definition using 7 self-reported CVH metrics (current smoking, physical inactivity, obesity, poor diet, hypertension, diabetes, and high cholesterol). Linked micromap plots and multilevel logistic models were used to examine state variation in poor CVH and to investigate the contributions of individual- and state-level factors to this variation. We found significant state-level variation in the prevalence of poor CVH (median odds ratio 1.32, P<0.001). Higher rates of poor CVH and cardiovascular disease mortality were clustered in the southern states. Minority and low socioeconomic groups were strongly associated with poor CVH and explained 51% of the state-level variation in poor CVH; state-level factors explained an additional 28%. State-level median household income (odds ratio 0.89; 95% CI 0.84–0.94), taxes on soda drinks (odds ratio 0.94; 95% CI 0.89–0.99), farmers markets (odds ratio 0.91; 95% CI 0.85–0.98), and convenience stores (odds ratio 1.09; 95% CI 1.01–1.17) were predictive of poor CVH even after accounting for individual-level factors. Conclusions There is significant state-level variation in poor CVH that is partly explained by individual- and state-level factors. Additional longitudinal research is warranted to examine the influence of state-level policies and food and physical activity environments on poor CVH.

Relation of Obesity to Circulating B-Type Natriuretic Peptide Concentrations in Blacks The Jackson Heart Study

Background— Lower plasma B-type natriuretic peptide (BNP) concentrations in obese individuals (“natriuretic handicap”) may play a role in the pathogenesis of obesity-related hypertension. Whether this phenomenon may contribute to hypertension in blacks is unknown. We tested the hypothesis that body mass index is inversely related to BNP concentrations in blacks. Methods and Results— We examined the relation of plasma BNP to body mass index in 3742 Jackson Heart Study participants (mean age, 55±13; 62% women) without heart failure using multivariable linear and logistic regression, adjusting for clinical and echocardiographic covariates. The multivariable-adjusted mean BNP was higher for lean participants compared with obese participants in both normotensive (P<0.0001) and hypertensive (P<0.0012) groups. In sex-specific analyses, the adjusted mean BNP was higher in lean hypertensive individuals compared with obese hypertensive individuals for both men (20.5 versus 10.9 pg/mL, respectively; P=0.0009) and women (20.0 versus 13.8 pg/mL; P=0.011). The differences between lean and obese participants were more pronounced in normotensive participants (men, 9.0 versus 4.4 pg/mL; P<0.0001; women, 12.8 versus 8.4 pg/mL; P=0.0005). For both hypertensive and normotensive individuals in the pooled sample, multivariable-adjusted BNP was significantly related to both continuous body mass index (P<0.05 and P<0.0001, respectively) and categorical body mass index (P for trend <0.006 and <0.0001, respectively). Conclusion— Our cross-sectional study of a large community-based sample of blacks demonstrates that higher body mass index is associated with lower circulating BNP concentrations, thereby extending the concept of a natriuretic handicap in obese individuals observed in non-Hispanic whites to this high-risk population.

Socioeconomic Position Is Positively Associated With Blood Pressure Dipping Among African-American Adults: The Jackson Heart Study

BACKGROUND Blunted nocturnal blood pressure (NBP) dipping is a significant predictor of cardiovascular events. Lower socioeconomic position (SEP) may be an important predictor of NBP dipping, especially in African Americans (AA). However, the determinants of NBP dipping are not fully understood. METHODS The cross-sectional associations of individual and neighborhood SEP with NBP dipping, assessed by 24-h ambulatory BP monitoring, were examined among 837 AA adults (Mean age: 59.2 ± 10.7 years; 69.2% women), after adjustment for age, sex, hypertension status, body mass index (BMI), health behaviors, office, and 24-h systolic BP (SBP). RESULTS The mean hourly SBP was consistently lower among participants in the highest category of individual income compared to those in the lowest category, and these differences were most pronounced during sleeping hours. The odds of NBP dipping (defined as >10% decline in the mean asleep SBP compared to the mean awake SBP) increased by 31% (95% confidence interval: 13-53%) and 18% (95% confidence interval: 0-39%) for each s.d. increase in income and years of education, respectively, after multivariable adjustment. CONCLUSIONS NBP dipping is patterned by income and education in AA adults even after accounting for known risk factors. These results suggest that low SEP is a risk factor for insufficient NBP dipping in AA.

Social Patterning of Cumulative Biological Risk by Education and Income Among African Americans

OBJECTIVES We examined the social patterning of cumulative dysregulation of multiple systems, or allostatic load, among African Americans adults. METHODS We examined the cross-sectional associations of socioeconomic status (SES) with summary indices of allostatic load and neuroendocrine, metabolic, autonomic, and immune function components in 4048 Jackson Heart Study participants. RESULTS Lower education and income were associated with higher allostatic load scores in African American adults. Patterns were most consistent for the metabolic and immune dimensions, less consistent for the autonomic dimension, and absent for the neuroendocrine dimension among African American women. Associations of SES with the global allostatic load score and the metabolic and immune domains persisted after adjustment for behavioral factors and were stronger for income than for education. There was some evidence that the neuroendocrine dimension was inversely associated with SES after behavioral adjustment in men, but the immune and autonomic components did not show clear dose-response trends, and we observed no associations for the metabolic component. CONCLUSIONS Findings support our hypothesis that allostatic load is socially patterned in African American women, but this pattern is less consistent in African American men.

Perceived discrimination is associated with health behaviours among African-Americans in the Jackson Heart Study

Background Using Jackson Heart Study data, we examined associations of multiple measures of perceived discrimination with health behaviours among African-Americans (AA). Methods The cross-sectional associations of everyday, lifetime and burden of discrimination with odds of smoking and mean differences in physical activity, dietary fat and sleep were examined among 4925 participants aged 35–84 years after adjustment for age and socioeconomic status (SES). Results Men reported slightly higher levels of everyday and lifetime discrimination than women and similar levels of burden of discrimination as women. After adjustment for age and SES, everyday discrimination was associated with more smoking and a greater percentage of dietary fat in men and women (OR for smoking: 1.13, 95% CI 1.00 to 1.28 and 1.19, 95% CI 1.05 to 1.34; mean difference in dietary fat: 0.37, p<0.05 and 0.43, p<0.01, in men and women, respectively). Everyday and lifetime discrimination were associated with fewer hours of sleep in men and women (mean difference for everyday discrimination: −0.08, p<0.05 and −0.18, p<0.001, respectively; and mean difference for lifetime discrimination: −0.08, p<0.05 and −0.24, p<0.001, respectively). Burden of discrimination was associated with more smoking and fewer hours of sleep in women only. Conclusions Higher levels of perceived discrimination were associated with select health behaviours among men and women. Health behaviours offer a potential mechanism through which perceived discrimination affects health in AA.