Current International Osteoporosis Foundation guidelines [13] recommended a target level of 30 ng/mL (75 nmol/L), which is associated with maximal suppression of parathyroid hormone (PTH), and defined vitamin D insufficiency as 25 (OH)D levels less than 20 ng/mL (50 nmol/L) and deficiency as levels less than 10 ng/mL (25 nmol/L). This evidence concerns the gene PTH and osteoporosis.