The role of C‐3 α epimer of 25‐hydroxyvitamin D on maintenance of bone mineral density

Abstract

The function of C‐3 α epimer (C‐3 Epi) of 25‐hydroxyvitamin D (25(OH)D) in vivo is unknown. In in vitro studies, C‐3 Epi is less potent in stimulating calcium transport but equivalent in suppressing parathyroid hormone. The objective was to compare C‐3 Epi to 25(OH)D and cholecalciferol in maintaining bone mineral density (BMD). Adult Sprague Dawley rats (12 weeks, n=36 female n=36 male) were randomized to: control AIN93‐M diet (2 IU vitamin D3/g food) or experimental diets for 8 weeks: C‐3 Epi at 0.5 and 1 IU/g food and a 25(OH)D group (0.5 IU/g food) reference group. Body weights and food consumption were measured weekly. Blood samples were collected at week 0, 4 and 8 as well as whole body dual‐energy X‐ray absorptiometry (DXA; QDR 4500A, Hologic). Differences were tested using a mixed model ANOVA. There were no differences among groups for weight or dietary intake. In females, the 1 IU C‐3 Epi group had higher whole body BMD compared to the cholecalciferol and 25(OH)D groups (Table 1); similar differences were observed in males (data not shown). These preliminary data suggest that C‐3 Epi is not detrimental to growth or bone. Future analyses including regional DXA and micro computed tomography plus biomarkers of bone metabolism are required to clarify the physiological responses. Research supported by NSERC and Dairy Farmers of Canada.