A Prospective Study of Serum 25-Hydroxyvitamin D Levels and Mortality Among African Americans and Non-African Americans

Lisa B. Signorello; Xijing Han; Qiuyin Cai; Sarah S. Cohen; Elizabeth L. Cope; Wei Zheng; William J. Blot

Disclosures

Am J Epidemiol. 2013;177(2):171-179. 

In This Article

Abstract and Introduction

Abstract

The beneficial biologic effects attributed to vitamin D suggest a potential to influence overall mortality. Evidence addressing this hypothesis is limited, especially for African Americans who have a high prevalence of vitamin D insufficiency. The authors conducted a nested case-control study within the prospective Southern Community Cohort Study to relate baseline serum levels of 25-hydroxyvitamin D (25(OH)D) with subsequent mortality. Cases were 1,852 participants who enrolled from 2002 to 2009 and died >12 months postenrollment. Controls (n = 1,852) were matched on race, sex, age, enrollment site, and blood collection date. The odds ratios for quartile 1 (<10.18 ng/mL) versus quartile 4 (>21.64 ng/mL) levels of 25(OH)D were 1.60 (95% confidence interval (CI): 1.20, 2.14) for African Americans and 2.11 (95% CI: 1.39, 3.21) for non-African Americans. The effects were strongest for circulatory disease death, where quartile 1 versus quartile 4 odds ratios were 2.53 (95% CI: 1.44, 4.46) and 3.25 (95% CI: 1.33, 7.93) for African Americans and non-African Americans, respectively. The estimated odds of total mortality were minimized in the 25(OH)D range of 35–40 ng/mL. These findings provide support for the hypothesis that vitamin D status may have an important influence on mortality for both African Americans and non-African Americans.

Introduction

Vitamin D, in addition to its established role in maintaining bone health, has been cited as a potential protective factor for a number of diseases, including certain cancers, cardiovascular disease, diabetes, and autoimmune disease.[1] A therapeutic role for vitamin D is being explored for many of these conditions.[2–6] Among the wide-ranging biologic effects attributed to vitamin D are the regulation of inflammation, cellular proliferation, cellular differentiation, angiogenesis, and apoptosis, which are key cancer-related mechanisms.[7] Vitamin D is also thought to play a role in regulating the immune and renin-angiotensin systems, insulin secretion, and thrombogenic activity.[8–10] Thus, it is reasonable to assume that vitamin D status, given its broad ramifications, may have the potential to influence overall mortality. The existing body of work addressing this question is still limited, and observational studies of circulating 25-hydroxyvitamin D (25(OH)D), the clinical measure of vitamin D status, in relation to all-cause mortality have, with few exceptions,[11–13] been relatively small, involving anywhere from 50 to 750 deaths.[14–21] Furthermore, African Americans are recognized as being at high risk for vitamin D insufficiency[1] and have mortality rates higher than any other racial group in the United States.[22] Yet the association between vitamin D status and overall mortality among African Americans is particularly understudied. The importance of vitamin D as a potential mediator of racial health disparities in the United States merits its exploration in relation to mortality in studies involving large numbers of African Americans.

Without randomized controlled trials designed to specifically address mortality endpoints, prospective cohort studies with baseline assessment of 25(OH)D can currently provide some of the most informative data to assess a potential link between vitamin D and mortality risk. Our objective was therefore to investigate the association between baseline serum 25(OH)D levels and subsequent mortality in a large, multiracial prospective cohort study.

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