Postmenopausal women are prone to osteoporosis because their natural estrogen concentrations drop sharply, resulting in bone loss. Menopause is characterized by the loss of estrogen production by the ovaries. The lack of estrogen enhances the ability of osteoclasts to absorb bone. On the other hand the osteoblasts (the cells which produce bone) are not encouraged to produce more bone. Soy isoflavones act as a weak form of estrogen and may therefore play a role in prevention of bone loss.
Numerous studies have tested the effects of isoflavones on bone health, but obtained results are not always conclusive. These studies look at the effects of isoflavones intake on bone mineral density, specific bone resorption markers (such as urine deoxypyridinoline), and bone formation markers (such as osteocalcin).
A recent meta-analysis published in Maturitas reviewed randomized control studies about the effects of isoflavones on bone mineral density or bone turnover makers in menopausal women. This study found that soy isoflavones significantly increased the bone mineral density of the lumbar spine and moderately decreased urine deoxypyridinoline, a bone resorption marker.
Taku and co-workers of the National Institute of Health and Nutrition, Tokyo, reviewed three meta-analyses on the effect of soy isoflavones on bone mineral density. Intake of soy isoflavones for six months was adequate to exert a beneficial effect on bone mineral density, especially of the lumbar spine. They also looked at two meta-analyses evaluating the effects of soy isoflavones on bone turnover markers and found that soy isoflavones did significantly reduce the levels of urine deoxypyridinoline, but had no significant effect on other bone markers. The authors concluded that soy isoflavones may prevent osteoporosis and improve bone strength in postmenopausal women.
Taku et al. Soy isoflavones for osteoporosis: An evidence-based approach. Maturitas. 2011 Sep 27