Osteoporosis is a condition characterized by low bone density and increased risk of bone fracture. Several dietary components have been shown to be associated with bone health. These include nutrients such as vitamin D, calcium, protein and vitamin K.
Vitamin K
According to "Advanced Nutrition and Human Metabolism," vitamin K, a fat-soluble vitamin, exists in several forms. Vitamin K-1, known as phylloquinone, is found in green leafy vegetables and plant oils. Vitamin K-2 is a group of compounds known as menaquinones. Vitamin K-2 is found in some animal products and is also produced by your own intestinal bacteria. The recommended daily intake of vitamin K is 90 mcg per day for women and 120 mcg per day for men.
Vitamin K Functions
A 2009 article published in the "Annual Review of Nutrition" states that the primary role of vitamin K in your body is as a facilitator of reactions that add carbon dioxide to specific proteins. The addition of carbon dioxide to proteins, known as protein carboxylation, activates and gives the protein its full functionality. Both vitamin K-1 and K-2 are equally effective in facilitating carboxylation reactions.
Vitamin K-dependent Proteins
Vitamin K is necessary for the carboxylation of proteins that are involved in a variety of biologic functions. For example, according to the "Annual Review of Nutrition," the proper function of proteins involved in the coagulation of blood is dependent on vitamin K. Other proteins involved in functions such as prevention of soft tissue calcification and bone metabolism are also dependent on vitamin K. Osteocalcin is one example of a vitamin K-dependent protein produced by the bone cells.
Bone
According to the National Osteoporosis Foundation, the risk of a bone fracture increases as you age. Fractures are greatly debilitating, painful and costly. It is important for older individuals to assess their fracture risk so preventative measures can be put in place. Bone health is most often assessed by measuring bone mineral density, or BMD. BMD is measured at several sites throughout your body including the hip, spine and wrist. A high BMD is associated with a lower risk of fracture.
Vitamin K and Bone
The "Annual Review of Nutrition" reports that large-population based studies have shown that low vitamin K status is associated with a low BMD and increased risk of fracture. The exact mechanism is not fully understood, but it is thought that osteocalcin, the vitamin K-dependent protein produced by bone cells, may not be fully functional when vitamin K concentration is low. Although observational studies suggest an association between vitamin K and bone health, an intervention study published in the "Journal of Clinical Endocrinology and Metabolism" did not shown a benefit of vitamin K supplementation on improving BMD. Current guidelines suggest a diet rich in green leafy vegetables, such as spinach, to obtain adequate vitamin K intake. Vitamin K supplementation, however, is not recommended to decrease the risk of bone fracture.
References
- "Annual Review of Nutrition";Roles for Vitamin K Beyond Coagulation; Sarah Booth; 2009
- "Journal of Clinical Endocrinology and Metabolism";Effect of Vitamin K Supplementation on Bone Loss in Elderly Men and Women; Sarah Booth, et al.;2008
- "Advanced Nutrition and Human Metabolism (fifth edition)"; 2009
- The National Osteoporosis Foundation
