However, the isoflavones did not slow bone loss at common fracture sites, according to results published in the American Journal of Clinical Nutrition.
Over 400 postmenopausal women participated in the multicenter, randomised, double-blind, placebo-controlled two year, which used either 80 or 120 mg of soy hypocotyl aglycone isoflavones (Frutarum’s SoyLife) plus calcium (400 mg) and vitamin D (400 IU).
Only the 120 mg per day produced benefits, with significantly reduced loss of whole body bone mineral density (BMD) after both one and two years.
“The attenuated whole body bone mineral density in healthy postmenopausal women for 2 y probably translates to minimal clinical benefits; yet the long-term significance, particularly with regard to fracture prevention, remains to be determined,” wrote the researchers, led by William Wong from the USDA/ARS Children’s Nutrition Research Center at the Baylor College of Medicine in Texas.
“The benefit of soy isoflavone supplementation at 120 mg/d in reducing the loss of whole body BMD, however, was not reflected in bone mineral content values among the regional sites or among the serum biochemical markers of bone metabolism,” they added.
With the World Health Organisation calling osteoporosis its biggest global healthcare problem, limiting bone loss in post-menopausal women could ease the burden of osteoporosis. According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is €31.7 bn in Europe.
Previous studies have reported conflicting results concerning soy isoflavones (40 to 99 mg/d doses) and bone health for postmenopausal women.
Wong and his co-workers recruited 403 postmenopausal women aged between 40 and 60 were recruited to participate in the study. Smokers and women already suffering from osteoporosis were not allowed to participate.
The women were randomly assigned to receive daily supplementation of soy hypocotyl aglycone isoflavones (80 or 120 mg) or placebo for two years. All the women were given calcium and vitamin D supplements.
After two years, the researchers recorded statistically significant smaller reduction in whole body BMD in the women receiving the 120 mg soy isoflavones, compared to the placebo group.
However, when compared with the placebo, soy isoflavone supplementation had no effect on changes in regional BMD, bone mineral content, or other biochemical markers of bone metabolism, said the researchers.
“It is possible that lifetime intake of soy is needed to see a significant protective association on bone mass conservation,” wrote the researchers.
The study was funded by the USDA and by the National Institutes of Health (NIH).
A meta-analysis published in the European Journal of Clinical Nutrition (doi: 10.1038/sj.ejcn.1602748) concluded doses of soy isoflavones less than 90 mg per day may improve bone density.
Previous studies from China have linked soy isoflavones to increases in bone mineral density (BMD), while a recent large study in the Archives of Internal Medicine (2005, Vol. 165, pp. 1890-1895) reported that high soy consumption was linked with a 48 per cent decrease in fractures for women who had been menopausal for less than 10 years.
Source: American Journal of Clinical Nutrition
November 2009, Vol. 90, No. 5, 1433-1439, doi:10.3945/ajcn.2009.28001
“Soy isoflavone supplementation and bone mineral density in menopausal women: a 2-y multicenter clinical trial”
Authors: W.W. Wong, R.D. Lewis, F.M. Steinberg, M.J. Murray, M.A. Cramer, P. Amato, R.L. Young, S. Barnes, K.J. Ellis, R.J. Shypailo, J.K. Fraley, K.L. Konzelmann, J.G. Fischer, E. O'Brian Smith