Vitamin D deficiency exists when the concentration of 25-hydroxy-vitamin D (25-OH-D) in the blood serum occurs at 12ng/ml (nanograms/millilitre) or less.

• 维生素D缺乏时，血清中25 -羟基维生素D （ 25羟D ）的浓度为12毫微克/毫升或更少。