Effects of Vitamin D3 Supplementation on Cardiovascular and Cancer Outcomes by eGFR in VITAL

Background Reduced 25-hydroxyvitamin D (25[OH]D) metabolism and secondary hyperparathyroidism are common with lower estimated glomerular filtration rate (eGFR) and may contribute to cardiovascular disease and cancer risk. Methods We assessed for heterogeneity by baseline eGFR of the effects of vitamin D-3 on cardiovascular and cancer outcomes in the Vitamin D and Omega-3 Trial (VITAL). Participants were randomized to 2000 IU vitamin D(3 )and/or 1 g omega-3 fatty acids daily using a placebo-controlled, two-by-two factorial design (5.3 years follow-up). Primary study end points were incident major cardiovascular events and invasive cancer. Changes in serum 25(OH)D and parathyroid hormone (PTH) were examined. Results Baseline eGFR was available for 15,917 participants. Participants' mean age was 68 years, and 51% were women. Vitamin D3 resulted in higher serum 25(OH)D compared with placebo (difference in change 12.5 ng/ml; 95% CI, 12 to 13.1 ng/ml), without heterogeneity by eGFR (P interaction, continuous eGFR=0.2). Difference in change in PTH between vitamin D3 and placebo was larger with lower eGFR (P interaction=0.05): -6.9 (95% CI, -10.5 to -3.4), -5.8 (95% CI, -8.3 to -3.4), -4 (95% CI, -5.9 to -2.2), and -3.8 (95% CI, -5.6 to -2) pg/ml for eGFR < 60, 60-74, 75-89, and >= 90 ml/min per 1.73 m(2), respectively. Effects of vitamin D3 supplementation on cardiovascular events (P interaction=0.61) and cancer (P interaction=0.89) did not differ by eGFR: HR=1.14 (95% CI, 0.73 to 1.79), HR=1.06 (95% CI, 0.75 to 1.5), HR=0.92 (95% CI, 0.67 to 1.25), and HR=0.92 (95% CI, 0.66 to 1.27) across eGFR categories for cardiovascular events and HR=1.63 (95% CI, 1.03 to 2.58), HR=0.85 (95% CI, 0.64 to 1.11), HR=0.84 (95% CI, 0.68 to 1.03), and 1.11 (95% CI, 0.92 to 1.35) for cancer, respectively. Conclusions We observed no significant heterogeneity by baseline eGFR in the effects of vitamin D3 supplementation versus on cardiovascular or cancer outcomes, effects on 25(OH)D and PTH concentrations.