Optimizing vitamin d concentrations for breast cancer risk reduction.

摘要

Vitamin D is a fat-soluble essential precursor to an active hormonal form that is an important regulator of numerous health conditions. Vitamin D is present naturally or is added to many foods, and is commonly taken as a dietary supplement. Vitamin D is converted to the active 25-hydroxyvitamin D form, or 25(OH)D, in the liver, and it is the form usually detected in serum as an indicator of vitamin D concentration. 25(OH)D is then converted in the kidney to the biologically active form 25-dihydroxyvitamin D (calcitriol). Food contains the vitamin D3 form, which is metabolized to 25(OH)D3. Vitamin D is also converted to the active form via sunlight exposure of unprotected skin to ultraviolet B radiation from the cutaneous 7-dehydrocholesterol to previtamin D3, which is then metabolized to vitamin D3. Calcitriol binds to the nuclear vitamin D receptor (VDR). The association of calcitriol to its receptor initiates normal transcription and leads to optimal gene expression.