Isoflavones and osteoporosisOsteoporosis, meaning "porous bone," is the degeneration of bone mineral density and bone strength. This process results in thinner and more porous bones and increases their susceptibility to fractures and deformations. Osteoporosis can develop anywhere in the skeleton, but most bone loss occurs in the spine, hips and ribs. The decline in estrogen levels associated with menopause puts women at increased risk for declining bone density and fractures. In the 5 years following menopause, women can lose up to 20 percent of their bone mass. But also older men can suffer from osteoporosis as their hormone levels also decrease. In order to fight osteoporosis it is important to practice sport and have adequate intake of vitamin D and calcium. Movements and physical activity are particularly important for the preservation of the bone mass because bones need some kind of resistance in order to become harder.
Effect of isoflavones on bone healthEstrogen is known to increase bone mass density and to improve bone turnover markers, but is associated with a higher risk of hormone related cancer. Therefore, many women seek alternatives to estrogen to improve their bone health. Studies show that, in spite of their significantly weaker estrogen action, isoflavones have bone building effects. This is the reason why in Asian countries osteoporosis is very rare after menopause, despite their low consumption of dairy products. Whereas genistein is mainly responsible for the reduction of menopausal symptoms, daidzein is the most protective isoflavone against osteoporosis. In the human body there is a constant process of breaking down and remaking of bones. The osteoclasts are cells which break down the bone, whereas the osteoblasts build up bone. If the activity of the osteoclasts is higher than that of the osteoblasts, there will be a gradual reduction of bone strength, leading to osteoporosis. Isoflavones inhibit the activity of osteoclasts, while stimulating the activity of osteoblasts. This moderate stimulus is sufficient enough to stimulate a continuous formation of bones.
ChenYu-Ming demonstrated that soy isoflavones have a beneficial effect on bone mineral content, especially in women who were over 4 years in menopause, had a lower body weight or a lower calcium intake . A study by Tsuang using quite large quantities of isoflavones (25mg/day) in ovariectomized rats, showed that isoflavones reduced bone loss and actually increased the bone mineral densities of long bones by up to 60% . A recent meta-analysis published in Maturitas and co-workers reviewed 5 studies about the effects of isoflavones on bone mineral density and bone turnover makers . They concluded that soy isoflavones significantly increased the bone mineral density of the lumbar spine and moderately decreased urine deoxypyridinoline, a bone resorption marker. Soy isoflavones may prevent osteoporosis and improve bone strength in postmenopausal women.
References Chen et al. Beneficial effect of soy isoflavones on bone mineral content was modified by years since menopause, body weight, and calcium intake: a double-blind, randomized, controlled trial. Menopause. 2004 May-Jun;11(3):246-54.
 Tsuang et al. Isoflavones prevent bone loss following ovariectomy in young adult rats. Journal of Orthopaedic Surgery and Research 2008, 3:12.
 Taku et al. Soy isoflavones for osteoporosis: An evidence-based approach. Maturitas. 2011 Sep 27
More literature about isoflavones and osteoporosisSoy isoflavones have a favorable effect on bone loss in Chinese postmenopausal women with lower bone mass: a double-blind, randomized, controlled trial. J Clin Endocrinol Metab. 2003 Oct;88(10):4740-7
The effects of phytoestrogen isoflavones on bone density in women: a double-blind, randomized, placebo-controlled trial. Am J Clin Nutr. 2004 Feb;79(2):326-33
Effects of Estrogen-Progestin on Risk of Fracture and Bone Mineral Density. JAMA. 2003;290:1729-1738
Soy Protein Has a Greater Effect on Bone in Postmenopausal Women Not on Hormone Replacement Therapy, as Evidenced by Reducing Bone Resorption and Urinary Calcium Excretion. The Journal of Clinical Endocrinology & Metabolism Vol. 88, No. 3 1048-1054
Effects of Phytoestrogens on Bone Turnover in Postmenopausal Women with a History of Breast Cancer. The Journal of Clinical Endocrinology and Metabolism Vol. 89, No. 3 1207-1212
Daidzein is more efficient than genistein in preventing ovariectomy-induced bone loss in rats. J Nutr. 2000 Jul;130(7):1675-81
The Soybean Isoflavone Genistein Induces Differentiation of MG63 Human Osteosarcoma Osteoblasts.. Journal of Nutrition. 2006 May;136(5):1166-70
Soy isoflavones attenuate bone loss in early postmenopausal Chinese women : A single-blind randomized, placebo-controlled trial.. Eur J Nutr. 2006 Jun 8