Vitamin K2 is widely used for the treatment of
osteoporosis in Japan. To understand the effects of
vitamin K2 on bone mass and bone metabolism, we reviewed its effects on the development of
osteopenia in rats, which characterizes models of
osteoporosis.
Vitamin K2 was found to attenuate the increase in
bone resorption and/or maintain bone formation, reduce bone loss, protect against the loss of trabecular bone mass and its connectivity, and prevent the decrease in strength of the long bone in ovariectomized rats. However, combined treatment of
bisphosphonates and
vitamin K2 had an additive effect in preventing the deterioration of the trabecular bone architecture in ovariectomized rats, while the combined treatment of
raloxifene and
vitamin K2 improved the bone strength of the femoral neck. The use of
vitamin K2 alone suppressed the increase in trabecular bone turnover and endocortical
bone resorption, which attenuated the development of cancellous and cortical
osteopenia in orchidectomized rats. In addition,
vitamin K2 inhibited the decrease in bone formation in
prednisolone-treated rats, thereby preventing cancellous and cortical
osteopenia. In sciatic neurectomized rats,
vitamin K2 suppressed endocortical
bone resorption and stimulated bone formation, delaying the reduction of the trabecular thickness and retarding the development of cortical
osteopenia.
Vitamin K2 also prevented the acceleration of
bone resorption and the reduction in bone formation in tail-suspended rats, which counteracted cancellous bone loss. Concomitant use of
vitamin K2 with a
bisphosphonate ameliorated the suppression of bone formation and more effectively prevented cancellous bone loss in tail-suspended rats.
Vitamin K2 stimulated renal
calcium reabsorption, retarded the increase in serum
parathyroid hormone levels, and attenuated cortical bone loss primarily by suppressing
bone resorption in
calcium-deficient rats while maintaining the strength of the long bone in rats with
magnesium deficiency. These findings suggest that
vitamin K2 may not only stimulate bone formation, but may also suppress
bone resorption. Thus,
vitamin K2 could regulate bone metabolism in rats, which represented the various models of
osteoporosis. However, the effects of
vitamin K2 on bone mass and bone metabolism seem to be modest.