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IOF World Congress Abstracts Experts discuss the potential role of vitamin K in the treatment of osteoporosis Vitamin K plays a pivotal role in bone metabolism and has been identified as a potential target for the treatment of osteoporosis and prevention of bone fractures, according to experts presenting today at a satellite symposium at the IOF World Congress on Osteoporosis, which brought together experts from Japan, the U.S. and France. Vitamin K is present in natto, a fermented soy product consumed in Japan, as well as in plant oils and some green vegetables such as alfalfa. Several recent observations have led to the theory that vitamin K deficiency may contribute to abnormal bone metabolism and bone fragility. Most significantly, epidemiological studies of Japanese subjects have established an inverse relationship between dietary intake of vitamin K and risk of hip fracture in both men and women. Furthermore, oral administration of vitamin K2 has been shown effective in increasing bone mineral density of patients with osteoporosis. Researchers at France's INSERM have confirmed the impact of vitamin K deficiency on bone metabolism by measuring serum levels of osteocalcin, a bone-specific protein that contains residues of the vitamin K-dependent amino acid GLA. They showed that levels of undercarboxylated osteocalcin in serum correlated negatively with hip bone marrow density (BMD), and were able to use this measurement to predict the risk of hip fracture in elderly women. Other studies described during the satellite symposium confirmed the relationship between low dietary intake of vitamin K and increased risk of hip fracture, but did not demonstrate a clear association between vitamin K intake and BMD. Furthermore, the putative mechanisms underlying the effects of vitamin K on bone are still unclear. Thus well-designed trials evaluating the effects of dietary vitamin K supplementation on age-related bone loss appear to be called for. Dr. Masataka Shiraki of the Research Institute and Practice for Involutional Diseases in Japan, reported the results of one such study: an open-label, randomized, prospective study in 362 osteoporotic women who were treated for three years with calcium (200 mg/day), with or without added vitamin K2 (as 45 mg/day menatetrenone). Patients were followed for three years and were assessed for measures of lumbar BMD, bone turnover markers and the incidence of clinical fractures. Lumbar bone mineral density, as measured by dual energy X-ray absorptiometry (DXA), decreased in both groups over the three-year treatment period; the difference was not statistically significant. In spite of this lack of difference in BMD, women in the vitamin K treatment group experienced significantly fewer clinical fractures (33 vertebral and 4 long bone fractures) as compared with those in the control group (54 vertebral and 10 long bone fractures). This suggests that vitamin K2 supplementation is effective in reducing the incidence of clinical fractures in women with osteoporosis, independent of its effects on bone mineral density. Vitamin K2 has been marketed in Japan since 1995 for the treatment of osteoporosis, but is not available in any other country at this time.
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