Vitamin D requirement and setting recommendation levels: long-term perspectives.

Target intakes of vitamin D to prevent rickets and osteomalacia are difficult to estimate because of the dual sources of vitamin D with dermal production and absorption from the intestine. However, vitamin D deficiency is associated with other diseases, e.g., myopathy, falls, fractures, autoimmune disorders, cardiovascular diseases, and malignancies, which underlines the necessity of redefining recommendations. A plasma level of 25-hydroxyvitamin D (25OHD) <50 nmol/L increases the risk of secondary hyperparathyroidism, whereas levels between 75 and 100 nmol/L appear optimal for maintaining general health. In adults, a minimum dietary intake of 17.5-25 microg/day is necessary to achieve these levels. Perspectives of future research are outlined here.