In our examination of a nationally-representative cohort representing 37.7 million adult individuals in the United States, we found that racial disparities in the prevalence of uncontrolled BP among Non-Hispanic Blacks when compared to Whites persist even after adjustment for demographic, socioeconomic status, clinical characteristics, and modifiable health behaviors in both the overall sample. Among a subsample with self-reported prior diagnoses of hypertension, the disparity in blood pressure control persisted for both Non-Hispanic Blacks and Mexican-Americans after adjustment for all covariates of interest. Further, among known hypertensive subjects, medication adherence was strongly associated with BP control, but did not explain the racial/ethnic disparity in the prevalence of uncontrolled BP. Last, after multivariate adjustment, only participants with self-reported levels of physical activity above 50 MET-hours/week had significantly lower odds of uncontrolled BP. To our knowledge, this is the first study to document the threshold of leisure-time physical activity associated with BP control among a nationally-representative sample utilizing a measure that incorporates duration as well as intensity and frequency of activity.
Differences in hypertension prevalence, treatment, and outcomes between minorities and non-Hispanic Whites have long been noted in the U.S. In a recent study, only 50% of hypertensive participants in NHANES were noted to have controlled hypertension, and Mexican-Americans were found to have higher prevalence of uncontrolled BP compared to non-Hispanic Whites.43
Our findings are consistent with prior literature, showing that age, race/ethnicity, and diabetes were associated with uncontrolled BP overall and among the subsample of known hypertensives.1, 31, 44, 45
We also noted that the minority groups did report lower sodium and alcohol intake as well as lower total energy intake than Whites; however, this did not impact the racial/ethnic disparity in BP control in multivariate regression modeling.
Furthermore, increasing levels of physical activity were associated with improved BP control overall and among hypertensives in NHANES, with extremely high levels of exercise (>50 MET-hrs/week) reaching statistical significance. Although a prior study examining NHANES III showed that greater than five episodes per week of moderate to vigorous activity was associated with decreased hypertension prevalence, frequency of activity was not assessed at that time.31
To put our findings in perspective, the current recommendation for exercise is equivalent to 7.5–12.5 MET-hours per week.46
White men in the highest quartile of leisure activity in the Atherosclerosis Risk in Communities (ARIC) study had 34% lower odds of developing hypertension over six years compared to the least active in multivariate models.10
Further, data from the Nurses’ Health Study, a sample of predominately White professional women, suggest that only the highest levels of activity were associated with decreased risk of incident hypertension.13
None of the self-reported health behaviors, including physical activity, mitigated the disparity in BP control in our study. This is consistent with findings in the ARIC study that although White men who reported high physical activity levels had lower odds of developing hypertension over time, baseline activity was not associated with incident hypertension in white women or blacks, even after controlling for other health behaviors.10
In the Coronary Artery Risk Development in (Young) Adults Study (CARDIA), accounting for lifestyle behaviors narrowed, but did not eliminate, the racial disparity in BP incidence that appeared after seven years of follow-up.47
However, this study did not include sodium intake in the analyses, and utilized a sample of adults who were relatively young (ages 18–30) at study entry. Thus, it is plausible that differences in dietary sodium intake (particularly if higher among Whites as was the case in the current study) may attenuate their findings. Alternatively, the influence of lifestyle behaviors on BP disparities may not persist as these individuals continue to age.
This study is subject to some limitations. First, NHANES is a cross-sectional study and thus temporal associations cannot be established. Second, the nutrient intakes were taken from a single 24-hour dietary recall for each subject. Since dietary recalls only cover one 24-hour period, it may not represent an individual’s usual intake if this period is not a typical diet day for the individual. However, the mean of the population’s distribution of usual intake can be estimated from a sample of individuals’ 24-hour recalls without sophisticated statistical adjustment.48
Third, in addition to nutrient intakes, many of the other behavioral and sociodemographic variables were from subject self-report, and therefore misclassification and reporting bias is a concern. Age, sex, obesity, and socioeconomic status have been associated with under-reporting dietary intakes and other self-reported health behaviors; however, it is unclear how this may relate to racial differences in self-reported nutrient intakes.49–52
For example, if racial/ethnic minority groups are more likely to under-report their caloric intake compared to non-Hispanic whites, and higher caloric intake is inversely related to blood pressure control, our findings of racial/ethnic disparities in control may underestimate the true magnitude of the racial/ethnic differences. Alternatively, if minorities are less likely to under-report caloric intake compared to non-Hispanic whites, our findings may overestimate the gap between minorities and non-Hispanic whites in rates of blood pressure control. Our findings should be interpreted in light of these limitations.
Last, there may be other variables that were not measured and/or included in our study that may impact the association of race with uncontrolled BP; i.e., occupational-related physical activity53
and/or exposure to psychosocial stressors such as discrimination. A recent study at a single academic medical center reported that Blacks reported more discrimination and concern about antihypertensive medications than Whites; after accounting for these factors, race was no longer a significant predictor of BP control.54
We also could not evaluate differences in health care provider behaviors such as adherence to prescribing guidelines or intensification of antihypertensive medications which may have a role in addressing racial/ethnic health disparities.55
In addition, racial/ethnic differences in genetic susceptibility, gene-environment interactions, and regional/geographic variations also may be more important contributors to the racial disparity in hypertension as well as other metabolic states (i.e., diabetes, obesity) that are associated with poor BP control.11, 56