Heightened risk of hypertension among black males: the masking effects of covariables.

Abstract

This study examines the extent to which a set of 10 demographic, behavioral, and medical risk factors explain black/white differences in hypertension. Data are from a cross-sectional examination of San Francisco transit drivers aged 25-65 years surveyed during 1983-1985 as part of an occupational health study. The inherent restriction of the study population to bus drivers and the further restriction to males in this population (764 blacks and 224 whites) controlled for factors related to occupation and sex. Control of 10 additional potential risk factors, including age, education, body mass index, smoking, and intake of caffeine and alcohol was possible in the analytic phase of the study. The unadjusted prevalence of hypertension (systolic blood pressure greater than or equal to 140 mmHg, diastolic blood pressure greater than or equal to 90 mmHg, or current use of antihypertensive medications) was 36.1 per cent for black males compared with 30.8 per cent for white males. The greatest difference in prevalence was observed for black males aged 55-64 years, for whom the prevalence was 46 per cent higher than for white males the same age. Despite higher rates of hypertension, blacks in all age groups exhibited lower levels of most major risk factors for hypertension. As a result, the independent effect of race on hypertension was increased rather than attenuated when the 10 covariables were taken into account (odds ratio of 1.27 in the unadjusted analysis, increasing to 1.54 in the adjusted, multivariate analysis). That this set of risk factors did not explain the higher rates of hypertension among blacks suggests that racial differences may arise from as yet unrecognized environmental and/or individual factors. The results also indicate that the association between race and blood pressure may have been underestimated in past studies that have relied on unadjusted analyses, in which negative confounding or masking effects of covariables have not been considered.