Summary: Substantial variability exists in the serum 25(OH)D increase observed in response to vitamin D supplementation. Measurement of circulating cholecalciferol and 24,25(OH)<inf>2</inf>D, as indicators of vitamin D absorption and degradation, respectively, account for approximately half of the variation in serum 25(OH)D observed following supplementation.Introduction: Vitamin D supplementation produces a variable response in serum 25(OH)D. This variability likely reflects, in part, differences in vitamin D absorption and/or degradation. Despite this variation in response, virtually all expert recommendations endorse a fixed vitamin D supplementation dose, an approach also used in most prospective studies. Such utilization of a single vitamin D dose does not assure attaining any pre-specified target 25(OH)D level, thereby compromising clinical care and prospective supplementation trials. This study begins addressing this weakness by exploring the feasibility of vitamin D metabolite measurements to predict serum 25(OH)D level attained following supplementation.Methods: Ninety-one community-dwelling postmenopausal women with baseline 25(OH)D of 10–30 ng/mL received oral vitamin D<inf>3</inf>, 2300 or 2500 IU, daily for 4–6 months. Serum 25(OH)D, cholecalciferol (D<inf>3</inf>), and 24,25(OH)<inf>2</inf>D were measured before and at the end of supplementation to determine if metabolite concentrations allow prediction of the 25(OH)D level attained.Results: From baseline and follow-up data, we derived a multiple linear regression model predicting posttreatment 25(OH)D as follows: final 25(OH)D = 8.3 + (1.05*initial 25(OH)D) − (7.7*initial 24,25(OH)<inf>2</inf>D) + (0.53*final D<inf>3</inf>) + (4.2*final 24,25(OH)<inf>2</inf>D). This model has an adjusted R<sup>2</sup> = 0.55, thus accounting for approximately half of the observed variance in the final 25(OH)D level.Conclusions: The contributions of circulating cholecalciferol and 24,25(OH)<inf>2</inf>D to this predictive model can be considered as indicators of intestinal absorption and clearance, respectively. This paradigm requires further study; it may allow efficient “treat-to-25(OH)D-target” strategies useful in optimizing prospective studies and clinical practice.
- 24,25-Dihydroxyvitamin D
- 25-Hydroxyvitamin D
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism