Is vitamin D a hormone or vitamin? ResearchGate Aug 2014
- Vitamin D itself - neither cholecalciferol (Vitamin D3) nor ergocalciferol (Vitamin D2)
- is not a hormone, but rather a biomodulator vitamin (capable of gene regulation);
- the primary active form 1,25-dihydroxyvitamin D (calcitriol) is a calcium-regulating hormone;
- the primary circulating non-active form 25-hydroxy-VitaminD is a prehormone,
converted peripherally to the active hormone 1,25-dihydroxyvitamin D (calcitriol).
Vitamin D is the structural raw material that one or more hormones or prehormones (not prohormones) are made from, and meets the strict definition of a vitamin, namely an organic substance present in minute amounts in the natural diet (foodstuffs, not supplements) that is essential to normal metabolism, and insufficient amounts of which in the diet may cause deficiency diseases
From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health
Dr. Norman 2008, full text online
Why "Vitamin D" is not a hormone, and not a synonym for 1,25-dihydroxy-vitamin D, its analogs or deltanoids.
Vieth R. 2004
Download the PDF from VitaminDWiki.