[Update on recent progress in vitamin D research. Vitamin D insufficiency/deficiency.]

Serum 25(OH)D level reflects bodily vitamin D store. Recently published "Assessment criteria for vitamin D deficiency/insufficiency in Japan" defines vitamin D sufficiency as 25(OH)D level of 30 ng/mL or more, vitamin D insufficiency as that of 20 to 30 ng/mL, vitamin D deficiency as that of less than 20 ng/mL. The lower the serum 25(OH)D level is, the higher the risks are, of secondary hyperparathyroidism, low bone mineral density, fall, fracture, rickets/osteomalacia, and hypocalcemia, as well as lower response to anti-osteoporosis medications. Beyond musculoskeletal disorders, vitamin D insufficiency/deficiency has been shown to be associated with various immunological, metabolic, and malignant disorders mainly by basic and epidemiological studies.