Influence of vitamins on the bone homeostasis

Bone tissue is a metabolically active system, constantly influenced by series of endogenic and external factors. Homeostasis of the bone tissue, as being dependent on the balance between bone resorption and osteogenesis as well as calcium homeostasis in the organism are correlated processes It is controlled by various hormones like active forms of vitamine D3 and A (retinoid acids), parathormone, calcitonine, sex hormones, glycocortycosteroids, thyroid hormones and growth factors. Locally active growth and/or differentiation factors, and other cytokines are also involved in the bone homeostasis control. Vitamins also play a major role in this process, among which vitamin D3, its active metabolites, vitamin A and its derivatives (acidic metabolites and synthetic analogues), vitamin E, K, C and some of B group can be found. A most significant influence on bone homeostasis is of vitamin D3 and its hydroxyl derivatives: 25(OH)D3, 1,25(OH)2D3, 24,25(OH)2D3, 1,24,25(OH)3D3 , vitamin A and its metabolites – retinoid acids. Vitamin D3 is responsible for correct bone development and mineralization. It takes a major part in calcium-phosphate metabolism regulation. Increases their intestinal absorption and balances eventual incorrect Ca/P ratio. vitamin D3 is required for ossification and production of bone components. The influence of physiologic concentration of retionol in the blood on bone remodulation is poorly known, nevertheless disadvantageous effect of both excessive concentration and deficiency of retinol on bones are known. Clinical applications of retinoids in skin diseases and oncological therapy is linked with an until recently underestimated toxic influence on bone tissue. Vitamin C also takes part in bone remodulation, through hydroxylation of proline and lysine, and facilitates formation of type I collagen. Osteoprotective action of vitamin E on bone matrix proteins is realized in anti-oxydative activity and inhibition of pro-inflammatory cytokines. Of all the group B vitamins, a major role in bone metabolism belongs to thiamin (B1), riboflavin (B2), pyridoxine (B6), cobalamine (B12) and folic acid. These vitamins act on bones metabolism in an indirect manner, through regulation of homocysteine level. The term “vitamin K” covers both natural (K1, K2) and synthetic (K3, K4) derivatives of naphthoquinone, all of similar biological, mainly anti-hemorrhagic activity. Clinical studies proved a connection betweeen low vitamn K consumption and low BMD and higher risk of bone fractures.