The Contribution of Baseline Weight and Weight Gain to Blood Pressure Change in African Americans

Abstract

PURPOSE: The positive association between obesity and blood pressure has been less consistent in African Americans than whites. This is especially true for African American men. This study investigated the sex-specific associations between baseline body mass index (BMI), weight change (kilograms), and five-year hypertension incidence and changes in blood pressure in a cohort of African Americans ages 25–50 years at baseline.

METHODS: The Pitt County Study is a longitudinal investigation of anthropometric, psychosocial, and behavioral predictors of hypertension in African Americans. Data were obtained through household interviews and physical examinations in 1988 and 1993.

RESULTS: Baseline BMI was positively and independently associated with changes in blood pressure after controlling for weight change and other covariates. When participants were stratified by sex-specific overweight vs. nonoverweight status at baseline, weight gain was significantly associated with increases in blood pressure only among the initially nonoverweight.

CONCLUSIONS: Baseline weight for all respondents, and weight gain among the nonoverweight at baseline, were independent predictors of blood pressure increases in this cohort of African Americans.

Introduction

Extensive epidemiologic evidence supports a positive association between relative weight, or obesity, and elevated blood pressure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. The strength of this association among African Americans is of particular interest because of the increased risk for hypertension (11) as well as obesity (especially for women) in this population 12, 13. Some inconsistency exists in the epidemiologic literature on weight and blood pressure in African Americans 3, 7, 14, 15, 16, 17, 18, 19, 20, 21. For example, data from the Coronary Artery Risk Development in Adults study (3), Evans County (17), Charleston (19), Lipid Research Clinic screenees (8), and the Hypertension Detection and Follow-up Program screenees (22), indicated a weaker association between excess weight and elevated blood pressure in blacks compared to whites. Quetelet’s index was not a statistically significant predictor of the incidence of hypertension among black residents of inner-city Baltimore, and weight change was associated with hypertension among only black women (23). In contrast, the relation between overweight and elevated blood pressure was essentially the same for blacks and whites in the Chicago Heart Association Detection Project in Industry (24) and the National Health and Nutrition Examination Follow-up Study (25). The majority of published studies on obesity and blood pressure are cross-sectional. For African Americans, especially, data are limited on the associations between baseline weight, weight change, and changes in blood pressure.

In the cross-sectional analysis of 1988 baseline data from the Pitt County Study (26), body mass index (BMI) was positively associated with systolic blood pressure (SBP), diastolic blood pressure (DBP), and hypertension prevalence among African Americans ages 25–50. In covariate adjusted analyses, a one standard deviation unit increase in BMI (4.2 for men and 6.8 for women) was associated with an increase of 2.7 mmHg in SBP for men and 3.4 mmHg in SBP for women. The corresponding values for DBP were 2.2 mmHg and 2.7 mmHg, respectively. In the current study, data from the 1993 follow-up survey were used to determine: 1) if baseline BMI was associated with five-year changes in blood pressure and hypertension incidence; and 2) if weight change over five years was independently associated with changes in blood pressure and incidence of hypertension.