Vitamin D activation is realized by means of complex mechanisms included within the physiological regulation of mineral metabolism. This review focuses on metabolic systems that lead to vitamin D synthesis. Evolution has made it necessary to satisfy the needs of increasingly complex organisms, which are moreover located in areas with in areas with ever less calcium availability. Although the mechanism is not yet completely clear, the outline that has emerged – in spite of its complexity – helps us understand the key role that nature has always attributed to this particular vitamin.
