"Isoflavone intervention significantly inhibits bone resorption and stimulates bone formation.
These favourable effects occur even if less than 90 mg/day of isoflavones are consumed or the intervention lasts less than 12 weeks," wrote the authors, lead by Professor P.Y. Wang from the School of Public Health, Peking University.
Previous studies have reported conflicting results concerning soy isoflavones (40 to 99 mg/d doses) and bone health for postmenopausal women.
But the new meta-analysis adds to the debate by reporting that such doses of soy isoflavones (less than 90 mg/d) 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
The reviewers focused on randomised controlled trials that measured the marker of bone resorption (degradation) - urinary deoxypyridinoline (Dpyr) - and the bone formation marker - serum bone-specific alkaline phosphatase (BAP).
Nine trials were identified using the three leading databases, PubMed, MedLine, and Embase.
In total, the trials contained 432 subjects.
The marker of bone resorption, Dpyr, decreased significantly in subjects who consumed isoflavones by 2.08 nmol/mmol, compared with non-consumers.
Moreover, significant decreases were observed even for isoflavone intakes of less than 90 mg/day (2.34 nmol/mmol), and with supplementation lasting less than 12 weeks (2.03 nmol/mmol), compared to placebo.
Bone formation markers were also found to increase, with BAP measures increasing by 1.48 micrograms per litre, compared to placebo, the reviewers stated.
Limiting bone loss in post-menopausal women could ease the burden of osteoporosis, a disease that affects half of all women over the age of 50.
According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is €31.7 bn in Europe.
Source: European Journal of Clinical Nutrition Published on-line ahead of print, doi: 10.1038/sj.ejcn.1602748 "Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta-analysis of randomized controlled trials" Authors: D-F Ma, L-Q Qin, P-Y Wang and R Katoh