[Effect of combined treatment with vitamin K2 and 1 alpha-(OH)-vitamin D3 on bone loss in ovariectomized rats].

Different types of therapeutic agents for osteoporosis are often simultaneously prescribed for the same patient, but limited experimental findings indicate the significance of combined treatment. In the present study, the inhibitory effect of combined vitamin K2(K2) and 1 alpha-(OH)-vitamin D3(D3) treatment on bone loss was compared to that of K2 or D3 alone in ovariectomized rats. Female rats (20-week-old) were ovariectomized and divided into 4 groups as follows: they were treated for 8 weeks with vehicle, K2 (30 mg/kg), D3 (0.3 microgram/kg) and K2 and D3 (K2 + D3) at the respective doses. K2 was given as a dietary supplement and D3 was orally administered 3 times a week. Bone density of the femurs was measured by peripheral quantitative computed tomography. Ovariectomy resulted in decreased bone density in proximal metaphysis, especially in the trabecular region, and treatment with K2, D3 or K2 + D3 inhibited this decrease. Moreover, in the K2 + D3 group, bone density and mineral content in the trabecular region in proximal metaphysis and cortical bone width in diaphysis were significantly higher than those in the D3 group. Consistent with these observations, bone strength in the femoral midshaft tended to increase only in the K2 + D3 group compared to that in the vehicle group. These findings indicate that combined K2 and D3 treatment is more effective for bone loss than that with K2 or D3 alone.