25-Hydroxyvitamin D, Parathyroid Hormone, and Mortality in Black and White Older Adults: The Health ABC Study

Abstract

Previous 25-hydroxyvitamin D [25(OH)D] and mortality studies have included mostly individuals of European descent. Whether the relationship is similar in Blacks and to what extent differences in 25(OH)D explain racial disparities in mortality is unclear. The objective of the study was to examine the relationship between 25(OH)D, PTH, and mortality in Black and white community-dwelling older adults over 8.5 yr of follow-up. Health ABC is a prospective cohort study conducted in Memphis, TN, and Pittsburgh, PA. Well-functioning Blacks and whites aged 71-80 yr with measured 25(OH)D and PTH (n = 2638; 49% male, 39% Black) were included in the study. Multivariate-adjusted proportional hazards models estimated the hazard ratios (HR) for all-cause, cardiovascular, cancer, and noncancer, noncardiovascular mortality (n = 691 deaths). Mean 25(OH)D concentrations were higher in whites than in Blacks [mean (sd): 29.0 (9.9) and 20.8 (8.7) ng/ml, respectively; P < 0.001]. Serum 25(OH)D by race interactions were not significant, however. Lower 25(OH)D concentrations were associated with higher mortality in Blacks and whites combined [HR (95% confidence interval [CI] 2.27 (1.59-3.24), 1.48 (1.20-1.84), and 1.25 (1.02-1.52) for < 10, 10 to < 20, and 20 to < 30 vs. ≥30 ng/ml]. In the multivariate model without 25(OH)D, Blacks had 22% higher mortality than whites [HR (95% CI) 1.22 (1.01, 1.48)]; after including 25(OH)D in the model, the association was attenuated [1.09 (0.90-1.33)]. The mortality population attributable risks (95% CI) for 25(OH)D concentrations less than 20 ng/ml and less than 30 ng/ml in Blacks were 16.4% (3.1-26.6%) and 37.7% (11.6-55.1%) and in whites were 8.9% (3.9-12.7%) and 11.1% (-2.7 to 22.0%), respectively. PTH was also associated with mortality [HR (95% CI) 1.80 (1.33-2.43) for ≥70 vs. <23 pg/ml]. Low 25(OH)D and high PTH concentrations were associated with increased mortality in Black and white community-dwelling older adults. Because 25(OH)D concentrations were much lower in Blacks, the potential impact of remediating low 25(OH)D concentrations was greater in Blacks than whites.