The small study followed 34 young Korean women for two years, with regular and detailed assessment of dietary intakes using 24-hour recall, supporting the reported benefits observed previously with postmenopausal women.
"Our study is the first study to assess soy isoflavones with multiple 24-hour recalls over 2 years; most other studies used Food Frequency Questionnaire at a single point," wrote lead author YoonJu
Song from Seoul National University in this month's issue of Nutrition Research .
"Our isoflavone intake measures thus represent average habitual isoflavone intake during the study."
Previous studies have reported 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 new study measured the bone mineral density (BMD) at the lumbar spine and femur of the women (average age 22.1) three times during the two-year period using dual x-ray absorptiometry.
The 24-hour dietary recalls, taken up to eight times with an average four months between the measurements, showed that the average intake of soybeans and isoflavones was 39 g and 8 mg per day, respectively.
Song and co-workers report that every one milligram of isoflavone intake was associated with a 0.26 per cent increase in bone mineral density per year in the neck of the femur, and a 0.31 per cent increase in the Ward's triangle area of the femur.
"Habitual soybean intake was low in this study though, and other dietary components also affect bone metabolism," cautioned the researchers.
"Therefore, future studies should address the interaction of isoflavones with other dietary components.
In this case, the mechanism of how isoflavones affect bone metabolism and the use of bone biomarker would result in a better understanding in young Asian women," they concluded.
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: Nutrition Research (Elsevier) Volume 28, Issue 1, January 2008, Pages 25-30 "Soybean and soy isoflavone intake indicate a positive change in bone mineral density for 2 years in young Korean women" Authors: Y.J. Song, H.Y. Paik, H. Joung