Whether the effects are repeatable in humans is not currently known, but the study has potential implications for soy-based infant formula as a means of reducing osteoporosis later in life, a condition that affects half of all women over the age of 50, according to the International Osteoporosis Foundation
Jovana Kaludjerovic and Wendy Ward from the University of Toronto looked at the effects of the soy isoflavones genistein, daidzein, a combination of the two, or control on the bone health of male and female mice starting during the first five days of life, until the age of four months (adulthood).
Writing in the Journal of Nutrition, Kaludjerovic and Ward report that female mice receiving the soy isoflavones had greater bone mineral density in the spine, compared to female animals receiving the control.
“Exposure to soy isoflavones during the first five days of life improved bone development in female CD-1 mice at young adulthood,” they wrote. “Moreover, the circulating levels of isoflavones in our mouse model after five days of injections were similar to those in human infants fed soy protein-based infant formulas.”
Soy and bone health
The role of soy and soy isoflavones in bone health is controversial, with studies reporting conflicting results concerning soy isoflavones (40 to 99 mg/d doses) and bone health for postmenopausal women. But a recent meta-analysis added to the debate by reporting that such doses of soy isoflavones (less than 90 mg/d) may improve bone density (Clinical Nutrition, doi:10.1016/j.clnu.2007.10.012).
Moreover, other studies from China have linked soy isoflavones to increases in bone mineral density (BMD), and 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.
The Toronto-based researchers used eight to 16 pups per gender per group and randomly assigned them to receive injections of the soy isoflavones, including genistein (2 mg per kg body weight), daidzein (5 mg per kg body weight), a combination of the two (7 mg per kg), the synthetic oestrogen compound diethylstilbesterol (2 mg per kg), or a control.
After four months, the researchers analysed the bone mineral density (BMD), and biomechanical bone strength. The data indicated that females receiving all the active interventions had greater BMD in the spine, compared to the control group. While no effects were observed in the male animals.
Furthermore, for females superior resistance to compression fractures was observed in the groups receiving daidzein and diethylstilbesterol. No effect of the joint daidzein – genistein combination was observed.
Improvements in markers of improved bone quality were also observed, but the specific mechanism behind the apparent benefit of daidzein still requires elucidation.
“Future studies should investigate the mechanisms by which daidzein and genistein modulate bone metabolism and whether benefits to bone development at four months of age can provide protection against the deterioration of bone tissue during aging that is associated with a decline in sex steroid production,” they concluded.
Source: Journal of Nutrition 2009, Volume 139, Pages 467-473, doi:10.3945/jn.108.100115 “Neonatal Exposure to Daidzein, Genistein, or the Combination Modulates Bone Development in Female CD-1 Mice” Authors: J. Kaludjerovic, W.E. Ward