Osteoporosis is the thinning of bone tissue and loss of bone mineral density. About 1 out of 5 American women over the age of 50 suffer from osteoporosis. This disease occurs when the body fails to form enough new bone or when too much existing bone is reabsorbed. The main cause of osteoporosis in aging women is a drop in estrogen. An effective treatment of osteoporosis is hormone replacement therapy, but many women are unwilling to start this treatment because of increased risk of breast and endometrial cancer. With their chemical structure similar to that of estrogen, soy isoflavones have been widely studied for their effects on bone health. Epidemiological studies show that women with high soy food consumption have a lower risk of osteoporosis than those consume a Western diet. However, clinical trials with soy isoflavones show conflicting results, probably because of small sample size and short trial duration.
Pan Wei and co-workers of the Sichuan University, China, conducted a meta-analysis from existing clinical trials and came to the conclusion that soy isoflavones supplements increase bone mineral density, an important indirect indicator of osteoporosis and fracture risk. They also found that soy isoflavones supplements decrease urinary deoxypyridinoline, a reliable marker of bone resorption. The researchers combined the results of 14 randomized controlled trials regarding the effect of soy isoflavones on osteoporosis. Soy isoflavones consumed for 1 month to 2 years increased bone mineral density by 54%, whereas urinary deoxypyridinoline decreased by 23%. The researchers believe that the beneficial effects of soy isoflavones is a results of their chemical similarity to human estrogen, which is known to increase bone mineral density in menopausal women.
Pan Wei et al. Systematic review of soy isoflavone supplements on osteoporosis in women. Asian Pacific Journal of Tropical Medicine. 2012 Mar;5(3):243-8.