Vitamin D as a Mediator of Racial Differences in Blood Pressure

Abstract

H ypertension is a cardinal risk factor for myocardial infarction, congestive heart failure, stroke, and death. Despite unfavorable trends in the prevalence of diabetes, obesity, and sedentary lifestyles, overall hypertension prevalence was stable at~29% between the 1999-2000 and 2007-2008 time periods 1,2 . This phenomenon has been attributed to improved hypertension awareness, higher treatment rates, and more intense regimens for hypertension. Unfortunately, overall hypertension prevalence among black Americans remains close to 40%, significantly higher than the level observed for whites and Hispanic groups 2,3 . Similar patterns of persistent racial differences despite overall improvement have been observed in cross-sectional studies of blood glucose levels and cholesterol levels 4 . Longitudinal studies also show increased odds of poor blood pressure control over time among Non-Hispanic blacks compared to whites 5 . In addition to increased prevalence of cardiovascular risk factors, mortality from coronary heart disease and stroke remain higher for blacks than other racial/ethnic groups 6 . Therefore, substantial interest exists to explain these persistent disparities and to devise interventions that can address them. In this issue of the Journal, Fiscella and colleagues present evidence that vitamin D deficiency is a potential mediator of racial differences in blood pressure between blacks and whites 7 . In an analysis of NHANES data from [2001][2002][2003][2004][2005][2006], they demonstrated that 25-hydroxyvitamin D (25-OH D) levels appeared to account for approximately one quarter of the difference in mean systolic blood pressure observed between black and white subjects. This study is notable because it is the largest and most robust to date to examine the effect of Vitamin D on racial disparities in blood pressure. The analysis is strengthened by a relatively large sample size with adequate power to detect differences between races based on vitamin D levels. The investigators also extensively adjusted for potential confounders of the relationship between black and white blood pressure measures.In addition to known effects on bone metabolism, Vitamin D has been the subject of intense investigation in recent years given interest in its other systemic effects. Observational studies have associated low vitamin D levels with increased risk for cancer, autoimmune diseases, diabetes, and cardiovascular disease including hypertension [8][9][10][11] While the findings in the present study are provocative, care should be taken in their interpretation. First, the crosssectional nature of the analysis precludes causal inferences. Though the investigators adjusted for key socio-demographic factors, patient-specific health conditions/behaviors, and biomarkers; the potential for bias and confounding remains. For example, information on psychosocial stress, medication non-adherence, and health literacy were not available for inclusion in this analysis. These factors have previously been implicated as mediators of rac...