[Vitamin K2 (menatetrenone) treatment increased bone strength in rats given low-calcium diets]

Two experiments were carried out in 4-week-old rats. First, the effect of dietary calcium (Ca) content (0.05, 0.1, 0.2, 0.5 and 1.16%) on bone loss was assessed for 3 weeks. Dry weight of the femur showed a Ca-content-dependent decrease. Significant decrease in body weight and plasma Ca level was observed in the 0.05 and 0.1% Ca diet groups, but not in other groups. Second, the curative effect of V.K2 on bone strength was examined. After being fed a 0.2%-Ca diet for 3 weeks, rats were fed 0.2%- or 0.5%-Ca diets for the next 6 weeks with or without V.K2 treatment. At the beginning and after 3 and 6 weeks of treatment, femurs and lumbar vertebra (L3) were collected. In the 0.2%-Ca group, bone mineral density (BMD) and bone strength in the femur gradually increased, but were much lower than those in the intact group. In the 0.5%-Ca group, both parameters in the femur and L3 were rapidly increased. V.K2 treatment did not affect the BMD or bone strength in the femur at either point. However, the bone strength in L3 in the V.K2 group was higher than that in the 0.5%-Ca group at 3 weeks and in the 0.2%-Ca group at 6 weeks than that in the respective control group. These findings suggest that V.K2 has curative effect on bone strength in the vertebra.