The roles of vitamins D and K in bone health and osteoporosis prevention

M. Shearer • 11/1/1997

Abstract

Vitamins D and K are two fat-soluble vitamins that play different but essential roles in bone metabolism. Vitamin D, after its conversion to a dihydroxylated metabolite, acts as a classical steroid hormone that regulates the transcription of manifold target genes involved with Ca homeostasis in general and bone mineralization in particular. The role of vitamin D in promoting mineralization of bone has of course been appreciated for many years, together with the deficiency syndromes of rickets and osteomalacia that result from prolonged deficiency states in childhood and adulthood respectively. Vitamin K, on the other hand, is a cofactor for a carboxylase enzyme that resides in several tissues and promotes the post-translational carboxylation of a number of specialized proteins with Cabinding properties. They include at least three osteoblastic bone proteins whose functions remain unclear. The synthesis of the best studied vitamin K-dependent bone protein osteocalcin is also regulated by vitamin D. This protein is also one of the ten most abundant vertebrate proteins and represents an interesting point of convergence of the different actions of vitamins D and K. Osteoporosis is a condition characterized by a low bone mass and microarchitectural deterioration of bone tissue that results in an increased bone fragility and increased fracture susceptibility. Neither the nature of osteoporosis (Marcus, 1996) nor its relationship to nutrition in the broad sense (Heaney, 1996; Prentice, 1997) will be considered here. Instead the nutrition and biochemistry of vitamins D and K will be outlined, followed by a consideration of the possible roles of each micronutrient in the pathogenesis and prevention of osteoporosis. If osteoporosis is viewed as being inseparably bound to the normal ageing process, then in the context of the present article it is obviously important to consider the consequences of any ageing process to the nutrition and metabolism of vitamins D and K. There is...

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