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Department of Medicine and Institute on Aging and Adult Life of The Medical School * Departments of Biochemistry and Nutritional Sciences of the College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI 53706
Although the abundance of vitamin K-dependent proteins in bone suggests an important function, the precise role of vitamin K in skeletal health remains to be determined. Serum concentrations of vitamin K are reportedly reduced in older individuals and persons with osteoporotic fracture. Whether this is causally related to vitamin K insufficiency or simply reflects inadequate nutritional status is unclear. Circulating levels of undercarboxylated osteocalcin may be a sensitive marker of vitamin K inadequacy and have been reported to be increased in both postmenopausal women and individuals who sustain hip fracture. It is also possible that vitamin K indirectly affects the skeleton via control of renal calcium excretion. The effect of vitamin K antagonists (oral anticoagulants) on both renal calcium excretion and bone density is controversial. Thus, many of the reports implicating a role for vitamin K insufficiency in the development of osteoporosis are conflicting. This review summarizes current knowledge regarding a possible role of vitamin K insufficiency in the pathogenesis of osteoporosis.
KEY WORDS: bone Gla protein (BGP) vitamin K matrix Gla protein (MGP) osteocalcin osteoporosis
1 To whom correspondence should be addressed.
Manuscript received 13 October 1994. Revision accepted 21 February 1995.