| [ Summary ] |
Vitamin D is essential for calcium homeostasis and formation of skeletal tissue. Dietary intake and synthesis in the skin are the sources of vitamin D. Vitamin D requirements can be met if the skin is exposed to an appropriate amount of sunlight. However if there is a lack of exposure to sunlight, induced vitamin D synthesis in the skin will not be a good source of vitamin D. To meet the vitamin D requirements without depending on sunlight exposure, dietary reference intakes and dietary intake guidelines for vitamin D have been set in Japan and other countries. Serum 25-OH-D concentrations are considered to be an appropriate indicator for judging the state of vitamin D levels. It is difficult to determine cut-off values for this nutrient. At the present time, 50 nmol/l and 75 nmol/l are proposed as the normal cut-off levels. According to a survey conducted in the United States, if the former values were used for analysis, more than half of the population would be classified as being deficient. If the latter figure is used, most of the population would be classified as deficient. Precise and reliable measurements of 25-OH-D are required. Controversy concerning this issue is being waged in many scientific journals. |