Answer to Question 1
Vitamin K participates in the metabolism of bone proteins, most notably osteocalcin. Without vitamin K, osteocalcin cannot bind to the minerals that normally form bones, resulting in low bone density. An adequate intake of vitamin K helps to decrease bone turnover and protect against fractures. The effectiveness of vitamin K supplements on bone health is inconclusive.
Answer to Question 2
Vitamin D raises blood concentrations of bone minerals in three ways. When the diet is sufficient, vitamin D enhances mineral absorption from the GI tract. When the diet is insufficient, vitamin D provides the needed minerals from other sources: reabsorption by the kidneys and mobilization from the bones into the blood. The vitamin may work alone, as it does in the GI tract, or in combination with parathyroid hormone, as it does in the bones and kidneys.
