[Vitamin D supplementation for everybody everytime?]

Only few foods contain vitamin D in higher concentrations. Therefore, the main source of vitamin D is the dermal synthesis under the influence of UVB-light. By enzymatic hydroxylation vitamin D is converted to 25-hydroxy-vitamin D and finally to the active hormone 1,25-dihydroxy-vitamin D, which plays an important role in calcium- and bone metabolism. Vitamin D-deficiency can result in demineralisation of the bone. The vitamin D-receptor is expressed by all nucleated cells of the body and vitamin D regulates many cellular functions. Sublinical vitamin D-deficiency is common even in the normal population resulting in a risk situation for at least osteoporosis and falls in older people. This is the reason for fortification of food in some countries by vitamin D. Also in Germany vitamin D-deficiency can be detected in many people leading to the question: is vitamin D supplementation necessary for everyone?