The vitamin D metabolite ratio (VMR) as a predictor of functional biomarkers of bone health

Summary Context The vitamin D metabolite ratio ( VMR ) (serum 24,25( OH ) 2 D 3 /25( OH )D 3 ) has been proposed as a biomarker of vitamin D sufficiency to replace serum 25( OH )D. Objective To examine the relationships of 24,25( OH ) 2 D 3 and VMR to functional biomarkers of bone health following vitamin D supplementation. Setting An ambulatory research centre. Design Serum from a previous research study of dose response of PTH , calcium absorption and bone turnover to vitamin D supplementation was analysed for vitamin D metabolites (25( OH )D, 24,25( OH ) 2 D 3 ). Outcome The relationship of serum 24,25( OH ) 2 D 3 and VMR to calcium absorption, PTH and bone turnover markers was examined. Results Although there were strong correlations of serum 25( OH )D with 24,25( OH ) 2 D 3 and free 25( OH )D, its correlation with VMR was lower. After vitamin D supplementation, the change in 25( OH )D, 24,25( OH ) 2 D 3 and VMR was associated with the change in calcium absorption, PTH and CTX . The correlation of the change in PTH with the change in metabolites was the lowest for VMR . Moreover, estimated dose response for standardized values of vitamin D metabolites showed a beta‐coefficient for VMR that was significantly less in magnitude compared to other metabolites. Conclusion Serum 24,25( OH ) 2 D 3 is closely associated with the dose response of serum 25( OH )D to vitamin D supplementation. However, the VMR does not appear to be equivalent to either of these metabolites in its response to increasing vitamin D intake or its association with PTH . It is unlikely that VMR will replace 25( OH )D as a biomarker for vitamin D sufficiency.