Understanding the Relationship between Skin Color, Vitamin D, and Blood Pressure.

Abstract

Understanding the intersection of skin color, behavioral factors and chronic disease risk is important in addressing underlying causes of race/ethnic disparities in blood pressure. Literature suggests that vitamin D impacts the renin-angiotensin system, vascular remodeling, and insulin resistance and thus, by extension, blood pressure. Previous research has identified that skin color is important to the cutaneous production of vitamin D, with the higher melanin content in darker skin reducing the amount produced from sun exposure. It is hypothesized that the high burden of hypertensive disease among African Americans as compared to Caucasians may be due in part to low serum vitamin D owed to darker skin color. This dissertation extends the research about health-related effects of vitamin D by examining its influence on blood pressure over time and quantifying its mediating effect on the relationship between skin color and blood pressure. This research used data from a population-based sample of mid-life African American and Caucasian women in southeastern Michigan enrolled in the Study of Women’s Health Across the Nation (SWAN) and followed annually from 1996 to 2010. The study found that skin color was an important contributor to circulating serum vitamin D in mid-life women over a 14-year period, with lighter skin color associated with higher vitamin D levels and higher odds of optimal vitamin D, defined as 75 nM. Independent of race, a skin color threshold for optimal vitamin D was identified. Additionally, vitamin D was an important correlate with baseline systolic blood pressure in African American and Caucasian women, however the change in vitamin D was not associated with systolic blood pressure over the study period. No association was observed between vitamin D and diastolic blood pressure. There was evidence that 11% of the relationship between skin color and systolic blood pressure was mediated by vitamin D. The relationship between skin color and systolic blood pressure was mediated by vitamin D. Establishing the effect of vitamin D on systolic blood pressure identifies a modifiable target for interventions aimed at ameliorating the high prevalence of hypertensive disease in the United States and the disproportionate burden among African Americans.