Japanese fermented soybean food as the major determinant of the large geographic difference in circulating levels of vitamin K2: possible implications for hip-fracture risk.

Increasing evidence indicates a significant role for vitamin K in bone metabolism and osteoporosis. In this study, we found a large geographic difference in serum vitamin K2 (menaquinone-7; MK-7) levels in postmenopausal women. Serum MK-7 concentrations were 5.26 +/- 6.13 ng/mL (mean +/- SD) in Japanese women in Tokyo, 1.22 +/- 1.85 in Japanese women in Hiroshima, and 0.37 +/- 0.20 in British women. We investigated the effect of Japanese fermented soybean food, natto, on serum vitamin K levels. Natto contains a large amount of MK-7 and is eaten frequently in eastern (Tokyo) but seldom in western (Hiroshima) Japan. Serum concentrations of MK-7 were significantly higher in frequent natto eaters, and natto intake resulted in a marked, sustained increase in serum MK-7 concentration. We analyzed the relation between the regional difference in natto intake and fracture incidence. A statistically significant inverse correlation was found between incidence of hip fractures in women and natto consumption in each prefecture throughout Japan. These findings indicate that the large geographic difference in MK-7 levels may be ascribed, at least in part, to natto intake and suggest the possibility that higher MK-7 level resulting from natto consumption may contribute to the relatively lower fracture risk in Japanese women.

[Serum concentration of vitamin K in elderly women with involutional osteoporosis].

Oral administration of vitamin K was reported to increase bone mineral density. However, the possible role of vitamin K in the pathogenesis of osteoporosis still remains unclear. Therefore, we measured the serum concentration of vitamin K1 and K2 (menaquinone-4, 7, 8) in 24 elderly women with osteoporotic vertebral compression fracture and in 36 elderly women without fracture. Major forms of vitamin K present in sera in this study were vitamin K1 and menaquinone-7. On the other hand, serum menaquinone-4 and -8 were undetectable in most women. Serum concentration of menaquinone-7 was significantly lower in women with fracture than in those without fracture (3.29 +/- 3.63 ng/ml vs 6.26 +/- 5.62, mean +/- SD, respectively), while no difference was found in serum vitamin K1 concentration (0.837 +/- 0.620 ng/ml vs 0.820 +/- 0.686, respectively). There was no difference between both groups in background data such as age, body height, body weight, and body mass index, as well as serum level of calcium, inorganic phosphate, creatinine, albumin, and alkaline phosphatase. These results suggest the possibility that deficiency of vitamin K, particularly that of menaquinone-7, is one of the risk factors for developing osteoporosis.