Soy isoflavones could help women with low bone mineral content prevent hip fractures in postmenopause years, suggest Chinese researchers in this month's Journal of Clinical Endocrinology and Metabolism.
Animal studies have shown that soy isoflavones have a preventative effect on oestrogen-related bone loss, but few data are available in humans, especially in Asian populations, said the team from the Chinese University of Hong Kong.
They carried out a double-blind, placebo-controlled trial on 203 postmenopausal Chinese women, aged from 48 to 62 years old. The subjects were randomly assigned to one of three treatment groups - a daily dose of either placebo, a medium isoflavone dose (0.5g starch, 0.5g soy extracts, and 40mg isoflavones) or a high isoflavone dose (1g soy extracts and 80mg isoflavones). All were given 500 mg of calcium and 125 IU of vitamin D3 in addition to their daily treatments.
The researchers measured bone mineral density (BMD) and bone mineral content (BMC) of the whole body, spine, and hip at baseline and one year after treatment. Women in the high dose group had mild, but a significantly higher improvement in BMC at the total hip and trochanter compared with the placebo and mid-dose groups, even after adjustments for potential confounding factors, said the scientists.
However further analyses revealed that the positive effects of soy isoflavone supplementation were observed only among women who started out with average or lower bone mineral content measurements.
"In conclusion, soy isoflavones have a mild, but significant, independent effect on the maintenance of hip BMC in postmenopausal women with low initial bone mass," write the researchers.
Their study supports findings of a review published in last month's American Journal of Clinical Nutrition (vol 78, no 3, 593S-609S). Dr Kenneth Setchell and Eva Lydeking-Olsen examined the evidence from 17 in vitro studies of cultured bone cells, 24 in vivo studies of animal models for postmenopausal osteoporosis, 15 human observational/epidemiologic studies, and 17 dietary intervention studies.
They found that "on balance, the collective data suggest that diets rich in phytoestrogens have bone-sparing effects in the long term, although the magnitude of the effect and the exact mechanism(s) of action are presently elusive or speculative".
Further research should examine these mechanisms to allow scientists to confirm the benefits of soy in bone health.