Does 1,25-dihydroxyvitamin D contribute to vitamin D paradox in healthy black women?

Document Type

Conference Proceeding

Publication Date

2-1-2022

Publication Title

J Bone Miner Res

Abstract

Vitamin D nutritional (VDN) status, as assessed by serum 25-hydroxyvitamin D (25- OHD) levels, is considered important for optimal bone health. However, a vitamin D paradox, characterized by lower 25(OH)D levels but superior bone health is usually seen in blacks. In contrast, 1,25-dihydroxyvitamin D (1,25(OH)2D) levels in blacks are increased. Since 1,25(OH)2D is an active vitamin D metabolite, we hypothesized that higher 1,25(OH)2D may stimulate bone formation and contribute to higher bone mass and strength in blacks.Accordingly, we studied 50 black and white women (25 in each group) matched for age, menstrual status, and BMI. Serum biochemical tests included 25-OHD, 1,25(OH)2D, calcium and parathyroid hormone (PTH). Bone histomorphometry was performed in cancellous bone in trans-iliac bone biopsies. The variables included bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), erosion surface (ES/BS), osteoclast surface (Oc.S/ BS), osteoid surface (OS/BS), osteoid thickness (O.Th), wall thickness (W.Th), osteoblast surface (Ob.S/BS), mineralizing surface (MS/BS), mineral apposition rate (MAR), mineralization lag time (Mlt), bone formation rate (BFR/BS) and activation frequency (Ac.f). The indices were compared between black and white groups using student t tests and ANCOVA analysis (Table 1).25-OHD was significantly lower but 1,25(OH)2D was significantly higher in blacks than in whites. There was no significant difference in calcium and PTH levels between the 2 groups. The bone histomorphometric results are shown in Table. Except for Tb.Th, which was significantly higher in blacks, there were no significant differences in other indices between the 2 races. The statistical results of bone histomorphometric indices from ANCOVA test (adjusted mean) were the same as those from t test (unadjusted mean). In ANCOVA model, serum 1,25(OH)2D level significantly affected OS/BS, W.Th, and ObS/ BS.The results of unadjusted means suggest that lower 25-OHD levels in black women do not compromise bone health. Adjusting for both 25-OHD and 1,25(OH)2D did not alter the statistical results for bone histomorphometry, implying that the bone health in black women is maintained by factors independent of VDN status. However, 1,25(OH)2D significantly affected the values of OS/BS, W.Th, and ObS/BS. We provisionally propose that 1,25(OH)2D is involved in the maintenance of bone health in blacks despite lower 25-OHD.

Volume

37

First Page

70

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