Abstract P037: Independent and Joint Associations of 25-Hydroxy Vitamin D and Parathyroid Hormone Levels With Cardiometabolic Biomarkers Among American White and Black Postmenopausal Women

Abstract

Introduction: Despite evidence of racial disparities in independent relationships of 25-hydroxyvitamin D (25[OH]D) and parathyroid hormone (PTH) status with cardiovascular risk, little is known about their joint associations with intermediate cardiovascular biomarkers. Hypothesis We hypothesized that there are White-Black differences in the direction and shape of the associations of total 25(OH)D and PTH with cardiovascular biomarkers of insulin resistance, beta cell function, systemic inflammation, and renal function among postmenopausal women. Methods: A random subcohort of 2,800 American White (n=1,500) and Black (n=1,300) postmenopausal women without cardiovascular disease (CVD) at baseline was selected from the Women’s Health Initiative Observational Study (N=93,676). We assessed plasma total 25(OH)D, PTH, high-sensitive C-reactive protein (hs-CRP), as well as creatinine-based glomerular filtration rate (GFR). Fasting glucose and insulin were measured to derive the homeostasis model assessment of insulin resistance (HOMA-IR) and beta cell function (HOMA-B). Weighted linear regression analyses were performed to assess independent and joint associations after adjusting for age, race/ethnicity, clinical center, education, body mass index, season of blood draw, smoking status, physical activity, alcohol consumption, postmenopausal hormone therapy use, and family history of CVD. Results: Total 25(OH)D levels were inversely associated with HOMA-IR among White women only (5.6% decrease per 1 SD increase in 25[OH]D; P for linear trend = 0.001). This association persisted among White women with PTH ≤65 pg/mL (5.9% decrease per 1 SD increase in 25[OH]D; P for linear trend = 0.001). While there was a linear trend towards higher 25(OH)D levels associated with lower GFR levels among White women with PTH ≤65 pg/mL (P for linear trend = 0.045), we found a non-linear relationship between total 25(OH)D and GFR among Black women with PTH >65 pg/mL (P for non-linearity = 0.001). Conclusions: Higher levels of total 25(OH)D, independently and jointly with PTH, were associated with lower HOMA-IR in White postmenopausal women. The shapes of the associations between total 25(OH)D and GFR markedly differed between White and Black women after accounting for PTH, suggesting potential racial disparities in vitamin D/PTH mechanisms underlying cardiovascular health.