[Update on recent progress in vitamin D research. Treatment of metabolic bone disorders by vitamin D.]

Vitamin D is indispensable for bone health and calcium metabolism, and decreased action of vitamin D causes various abnormalities in bone metabolism. Severe vitamin D deficiency causes osteomalacia/rickets. Even milder vitamin D insufficiency could still be harmful for bone health via secondary hyperparathyroidism and bone loss, and could also lead to increased risk of falling. Osteomalacia/rickets associated with impaired vitamin D action should be treated by either native or active vitamin D ₃ , depending on its etiology. As for osteoporosis, vitamin D repletion is important to adequate therapeutic effects of anti-resorptives. As a monotherapy, eldecalcitol, active vitamin D ₃ analogue, has been shown to increase bone mineral density and to decrease the incidence of vertebral fractures with significantly greater efficacy compared to active vitamin D ₃ .