Soy Isoflavone Increases Bone Mineral Density in Post-Menopausal Women

by | Jul 1, 2008 | 2007, Bone Health, Menopause, Soy Isoflavones, Women's Health - Bone Health

Written by Susan Sweeny Johnson, PhD, Biochem. In a review including ten researches with a total of 608 subjects, soy isoflavone significantly increased bone mineral density.

Osteoporosis, a decrease in the density of the bones leading to sensitivity to fracture, is very common among post-menopausal Caucasian women. Since before menopause, estrogen levels are higher, estrogen replacement therapy is sometimes prescribed for post-menopausal women at risk for osteoporosis who want to minimize bone mineral loss (1,2). However, the effects of estrogen on the body are complex, so estrogen replacement comes at a price, including increased risk for heart disease and breast cancer (3). Soy isoflavone can act as estrogen mimics and supplementation with them has become a popular alternative to hormone replacement therapy (4,5). However, studies examining the effectiveness of soy isoflavones in increasing bone mineral density in post-menopausal women have yielded contradictory results (6).

In an effort to determine if the combined results of the previously published studies on the increase in bone mineral density or content with intake of soy isoflavones are significant, the researchers recently selected 10 published studies out of 675 potential ones. The majority were eliminated from inclusion because they were not randomized or controlled. The ten studies (608 subjects) which were included in the meta-analysis examined soy protein intake (containing a known amount of isoflavones) over a period of six months or more in peri or post-menopausal women and included a control group.  Results were reported using changes in spine bone mineral density (SBMD) and spine bone mineral content (SBMC) from baseline.

When the 10 studies were analyzed together, intake of isoflavones significantly increased SBMD by 20.6 mg/cm2 (95% confidence interval, CI = 4.5–36.6 mg/cm2, p = 0.01). Subgroup analysis showed that more than 90 mg per day of isoflavone supplementation was necessary to see significant change, and that post-menopausal women benefited more significantly than peri-menopausal women. SBMC also improved with supplementation but to a less significant degree.

“More than 1.3 million hip, spine and wrist fractures each year are attributable to osteoporosis. Low bone density is a major cause of fractures. Data from the National Health and Nutrition Examination Survey, using a definition of osteoporosis developed by the World Health Organization, determined that up to 20% of white women over 50 have osteoporosis and up to 50% have low bone mass. Non-white women and men have lower rates of osteoporosis but contribute up to 25% of the fractures annually (7).

Low trauma fractures at any site in the elderly are largely due to low bone mass. Hip fractures are the most devastating and costly osteoporotic fractures. Death in the months immediately following hip fracture is not uncommon but is often attributed to other causes such as pneumonia. Fifty percent of surviving individuals will need help with daily living activities, and 15 to 25 percent will need to enter a long-term care institution shortly after the fracture (8). In 1995 the annual national cost of all osteoporosis-related fractures was estimated at $13.8 billion dollars (9). Some projections have forecast a more than 3-fold increase in the number of hip fractures due to the aging of the U.S. population (10)(11).

Source: Ma, De-Fu, et al. “Soy isoflavone intake increases bone mineral density in the spine of menopausal women: meta-analysis of randomized controlled trials.” Clinical nutrition 27.1 (2008): 57-64.

© 2007 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism.

 Posted July 1, 2008.

References:

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  11. See the National Institutes of Health website.