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Vitamin D Pro-Hormone

Meaning

Vitamin D is accurately classified as a pro-hormone, meaning it is a precursor substance that must undergo two sequential metabolic conversions to become the fully active steroid hormone, calcitriol (1,25-dihydroxyvitamin D). The initial form, cholecalciferol (Vitamin D3), is acquired from sun exposure or diet and is biologically inert until these metabolic steps are completed. This classification underscores its systemic role in gene regulation and calcium homeostasis, extending far beyond simple vitamin function.