Vitamin D Metabolite Ratio as a Marker of Bone Turnover and Change in Volumetric Bone Mineral Density in Older Men

Background: The vitamin D metabolite ratio(VMR), calculated by the ratio of 24,25-dihydroxyvitamin D3 to 25-hydroxyvitamin D(25[OH]D3), is a marker of vitamin D stores that may be a better predictor of bone health outcomes than 25(OH)D. Previously, we found that a higher VMR was cross-sectionally associated with higher volumetric bone mineral density (vBMD) in older men. In this analysis we examined the relationship between the VMR and 25(OH)D with biomarkers of bone turnover (BTM’s) and changes in vBMD in older men in the Osteoporotic Fractures in Men (MrOS) study. Methods: We used multiple linear regression models to evaluate the relationship between the VMR and 25(OH)D with BTM’s, including parathyroid hormone(PTH), C-terminal telopeptide of type I collagen(CTX-I) and N-terminal propeptide of type I procollagen(PINP). vBMD was assessed at the distal radius and tibia by high resolution peripheral quantitative computed tomography (HRpQCT). We similarly evaluated the relationship of the same vitamin D measures with annualized percent change in vBMD. Results: 254 men with repeat measures of vBMD were included in this analysis. Mean time (SD) between scans was 6(0.6) years. Mean age of participants was 83(3.3) years, with a mean eGFR of 71(14)mL/min/1.73m2, and 22% had chronic kidney disease (eGFR < 60). Mean VMR and 25(OH)D were 6.5(2.2)[(ng/mL)/(ng/mL)] and 39(14)ng/mL, respectively. Mean PTH, CTX-I and P1NP were 50(30) pg/mL, 0.29 (0.18) ng/mL and 50(23) ng/mL, respectively. In fully adjusted models both VMR and 25(OH)D were inversely associated with parathyroid hormone concentrations (Table), but only the VMR was inversely associated with CTX-I. Neither VMR nor 25(OH)D was associated with a marker of bone formation or annualized change in vBMD. Conclusion: In community living older men, only the VMR was inversely associated with a marker of bone resorption, CTX-I. Neither VMR nor 25(OH)D was associated with a marker of bone formation or annualized change in vBMD. Further studies are needed to evaluate how the VMR may affect bone longitudinally. Funding: NIDDK Support - NIDDK Support, NIDDK Support