Which of the following decreases the conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol?

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[VII C 1]. $\mathrm{Ca}^{2+}$ deficiency (low $\mathrm{Ca}^{2+}$ diet or hypocalcemia) activates $1 \alpha$-hydroxylase, which catalyzes the conversion of vitamin $\mathrm{D}$ to its active form, 1,25-dihydroxycholecalciferol. Increased parathyroid hormone (PTH) and hypophosphatemia also stimulate the enzyme. Chronic renal failure is associated with a constellation of bone diseases, including osteomalacia caused by failure of the diseased renal tissue to produce the active form of vitamin $\mathrm{D}$.

Which of the Following Decreases the Conversion of 25-Hydroxycholecalciferol to 1,25-Dihydroxycholecalciferol