Vitamin D interactions with soy isoflavones on bone after menopause: a review

Abstract

Vitamin D is known to increase Ca absorption in adults. However, the threshold vitamin D status to benefit Ca absorption is lower than the target vitamin D status for higher bone mineral density and lower fracture risk, pointing to another pathway for vitamin D to benefit bone. One possibility is by affecting osteoblast and osteoclasts directly. Vitamin D-related bone metabolism may also be affected by soy isoflavones, which selectively bind to the estrogen receptor β and may reduce bone loss in postmenopausal women. We discuss a possible synergistic effect of soy isoflavones and vitamin D on bone by affecting osteoblast and osteoclast formation and activity in postmenopausal women.

Figure 1

Possible mechanisms of the effect of soy isoflavones and vitamin D on bone metabolism. Soy isoflavones and vitamin D (VD) can synergistically stimulate bone formation through inducing 1,25-dihydroxyvitamin D synthesis and vitamin D receptor (VDR) expression. 1,25(OH)₂D bound to VDR can induce osteoblast activity and bone formation. Also, bone resorption may be reduced through inducing estrogen receptor (ER) expression, which is affected by VD and soy isoflavones. An increase in ER can lead to an increase in OPG formation and thus prevents osteoclast (OC) maturation, resulting in less bone resorption.