Prospective association of vitamin D concentrations with mortality in postmenopausal women: results from the Women's Health Initiative (WHI).

BACKGROUND: Prospective epidemiologic data on the association between vitamin D and all-cause and cause-specific mortality are limited.
OBJECTIVE: This study aimed to determine whether 25-hydroxyvitamin D [25(OH)D] concentrations were prospectively and independently associated with cardiovascular disease (CVD), cancer, and all-cause mortality in postmenopausal women.
DESIGN: A substudy in 2429 postmenopausal women within the Women's Health Initiative (WHI) with measured baseline 25(OH)D concentrations were followed for 10 y for death from CVD, cancer, and all-cause mortality. Proportional hazards models were performed to evaluate quartiles of month-adjusted 25(OH)D concentrations, with adjustment for potential confounders. Sequential model building and analysis for multiplicative interaction were performed to evaluate the effects of central adiposity on the association of low 25(OH)D with all-cause mortality.
RESULTS: Of the 2429 women, 224 deaths occurred, with 79 deaths from CVD and 62 deaths from cancer. Multivariate-adjusted HRs that compared quartiles 1 (lowest) to 4 (highest) of 25(OH)D for all-cause mortality (HR: 1.25; 95% CI: 0.80, 1.95), CVD mortality (HR: 1.27; 95% CI: 0.81, 1.99), and cancer mortality (HR: 1.39; 95% CI: 0.88, 2.19) were not significant. There was a potential interaction (P = 0.08) between abdominal obesity and low 25(OH)D concentrations that showed an increased risk of the lowest quartile of 25(OH)D concentrations (HR: 1.85; 95% CI: 1.00, 3.44) with increased mortality in women with a normal waist circumference but no increased risk in women with abdominal obesity (HR: 0.96; 95% CI: 0.52, 1.76).
CONCLUSION: Body fat distribution may play an important role in the modulation of the effect of low vitamin D concentrations on health. This trial was registered at clinicaltrials.gov as NCT 00000611.