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Clnical Research : Osteoporosis (3)
Vitamin K
Vitamin K has been known for many years to be involved in the synthesis of a number of proteins (vitamin K dependent proteins) by acting as a co-factor for their carboxylation 34. Vitamin K's most well understood function is as a co-factor for proteins involved in blood coagulation; however, vitamin K dependent proteins have also been identified in bone 35. One of these proteins, osteocalcin, is involved in regulating bone mineralization 36, and may require more vitamin K than the proteins involved in blood coagulation in order to function properly 37. This has lead to the concept that current intake of vitamin K may be less than adequate and supplemental vitamin K may be beneficial for optimal bone health.
A number of observations have related vitamin K to bone. Postmenopausal bone loss is associated with poor vitamin K intake, and patients with hip fractures have been reported to have very low circulating concentrations of vitamin K 38-39. Additionally, circulating concentrations of undercarboxylated osteocalcin have been reported to be inversely correlated with bone density in the hip 40. It has also been observed that supplementation of post-menopausal women with 1 mg vitamin K for 2 weeks increases serum markers of bone formation and may reduce urinary losses of calcium 41. However, data with respect to the effect of supplemental vitamin K on bone mass or fracture are limited. One Japanese study, 42 has shown a significant reduction in postmenopausal bone loss in women receiving supplemental vitamin K. Similar studies from Western countries assessing the effect of supplemental vitamin K are being awaited.
Manganese, Copper, Zinc and Vitamin C
The role that manganese, copper, zinc and vitamin C play in the metabolism of bone has been extensively investigated. Nonetheless, compared with calcium and vitamin D 3 their exact biochemistry with respect to bone metabolism is not as well understood. Copper and vitamin C are both required for the proper formation of collagen. Additionally, vitamin C plays a role in the formation of glycosaminoglycans. Manganese is involved in the synthesis of mucopolysacchrides that are essential for the formation of the bone matrix, and zinc deficiency causes a reduction in collagen synthesis and osteoblasts (cells involved in the formation of new bone) activity. Cross-sectional and animal data report the diets deficient in manganese and copper are associated with a lower bone mineral density. Saltman and Strause 43 supplemented post-menopausal women with either 1) 1000mg/d calcium citrate, 2) trace minerals (5mg/d copper, 2.5 mg/d manganese, and 15 mg/d zinc), 3) a combination of calcium and trace minerals, or 4) a placebo for 2 y. Women receiving the trace minerals plus calcium lost significantly less bone mineral density compared with placebo. Neither the minerals nor the calcium alone showed a significant difference compared with placebo. These data suggest an important interaction between calcium and trace minerals in the prevention of bone loss in postmenopausal women.
Magnesium
Given that sixty percent of all the magnesium in the body is located in bone, it is reasonable to conclude that magnesium is also closely related to bone structure and function. Magnesium status has been shown to influence various parameters that affect bone metabolism. Magnesium deficiency has been associated with the inhibition of parathyroid hormone release and increased resistance to parathyroid hormone. Additionally, magnesium deficiency is associated with a decreased concen-tration of serum vitamin D3 and results in tissue resistance to the action of vitamin D3 . Prospective studies examining the effect of supplemental magnesium on bone density are very limited. Rude and Olerich supplemented 5 patients with gluten sensitive enteropathy (who often have malabsorption problems) with 504 -576 mg/d magnesium. Supplementation for 2 years resulted in an increase in bone mineral density and an increase in serum parathyroid hormone. No other data on magnesium supplementation and bone parameters are available. |