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This product is a vitamin drug. Vitamin D2 promotes the absorption of calcium by the brush border of the small intestinal mucosa and the reabsorption of phosphorus by the renal tubules, increases the concentrations of blood calcium and phosphorus, and cooperates with parathyroid hormone and calcitonin to promote the release of calcium phosphate from old bones, maintaining and regulating normal plasma calcium and phosphorus concentrations. Vitamin D2 promotes the deposition of calcium in new bone formation sites, deposits citrate in bones, promotes bone calcification and the maturation of osteoblast function and bone-like tissue. After vitamin D2 is ingested, it is catalyzed by the 25-hydroxylase system in the cell microsomes to produce calcidiol (25-OHD3), which is catalyzed by the 1-hydroxylase system in the renal proximal tubular cells to produce biologically active calcitriol (1-25-(OH)2D3).