By Caroline Kanzaiza
varian hormone deficiency is a major risk factor for osteoporosis in postmenopausal women. Hormone replacement therapy (HRT) is one of the treatments used to alleviate postmenopausal symptoms; to lower the risk for coronary heart disease and perhaps it could be the most effective treatment for osteoporosis, since it has been demonstrated to both reduce the rate of bone loss and risk of fracture. However, more than 80% of postmenopausal women do not consent to hormone replacement therapy, either because of fear of increased risk of certain types of cancer or contraindications. As a result, postmenopausal women are more inclined to use natural remedies to alleviate these symptoms and help reduce their risk for chronic diseases such as osteoporosis. Recent reports show that certain bioactive constituents, such as phytoestrogens, which are non-steroidal plant compounds naturally found in fruits, vegetables, and grains play a role in maintaining or improving bone health. Phytoestrogens act like selective estrogen receptor modulators in tissues. Hence dietary intake of food sources high in phytoestrogens such as soybeans, flaxseed, and certain types of fruits and vegetables high in polyphenolic compounds may provide a practical and safe alternative treatment in postmenopausal women.
Several animal and human studies have been conducted to assess the role of soy or its isoflavones on bone health. For example, a six-month study conducted to examine the lipid-lowering properties of soy protein in postmenopausal women showed that isoflavone-rich soy protein increased lumbar spine bone mineral density (BMD) and bone mineral content (BMC). Another study of similar duration indicated that the percentage change in lumbar spine bone mineral density (BMD) or bone mineral content (BMC) in perimenopausal women did not decline from baseline in the isoflavone-rich soy group, but significantly declined in the control group that received isoflavone-poor supplement.
Results from a trial conducted to evaluate the effects of soy protein isolates with three levels of isoflavones on markers of bone turnover in 14 premenopausal and 17 postmenopausal women, concluded that, effects of soy isoflavones on markers of bone turnover were of small magnitude and unlikely to be clinically relevant. However, another study involving 50 postmenopausal women who received 60–70 mg of isoflavones in the form of soymilk for 12 weeks demonstrated reduction in the rate of bone resorption and enhanced the rate of bone formation. This is supported by unpublished data obtained from a trial, involving consumption of 40 g soy protein delivering 90 mg isoflavones daily for a period of three months which significantly indicated reduced urinary deoxypyridinoline (Dpd) excretion and elevated serum insulin-like growth factor I (IGF-I) concentrations in women under or above age 65 regardless of their estrogen status. The above results show inconsistencies that could be attributed to numerous confounding factors such as age, menopausal status and isoflavone content of the soy regimens provided.