VitaminDBildung

VitaminDBildung refers to the formation and activation of vitamin D in humans. It encompasses cutaneous synthesis, dietary intake, and the metabolic steps that convert vitamin D into its active forms. The term is a coinage that combines vitamin D with the German word Bild­ung (formation) to describe this process.

Endogenous synthesis begins in the skin, where ultraviolet B (UVB) radiation converts 7-dehydrocholesterol to previtamin D3, which then becomes vitamin D3. Vitamin D is transported to the liver, where it is hydroxylated to 25-hydroxyvitamin D (25(OH)D), the main circulating form and common biomarker for status. In the kidneys, 25(OH)D undergoes further hydroxylation to 1,25-dihydroxyvitamin D (calcitriol), the biologically active hormone that binds the vitamin D receptor and regulates calcium and phosphate homeostasis. Local production of active vitamin D can also occur in other tissues.

Sources of vitamin D include sunlight, fatty fish, fortified foods, and dietary or over-the-counter supplements. The amount of cutaneous vitamin D production depends on latitude, season, time of day, skin pigmentation, age, and sunscreen use.

Functions of VitaminDBildung extend to calcium and phosphate absorption, bone mineralization, and modulation of immune function and cellular growth. Deficiency can lead to rickets in children and osteomalacia in adults; excessive intake can cause toxicity, though that is uncommon with typical dietary and sun exposure patterns.

Assessment relies on serum 25(OH)D levels, with guidelines varying by authority. Common recommendations for daily intake range around 600–800 IU for adults, adjusted for age, sun exposure, and individual risk factors.