Soy Isoflavones Protect Postmenopausal Women From Bone Loss

News Author: Laurie Barclay, MD
CME Author: Charles Vega, MD, FAAFP

Posted: 7/14/2006

July 14, 2006 -- Soy isoflavones (SoyLife) may protect against bone loss in postmenopausal women, according to the results of a single-blind, randomized trial reported in the June 8 Online First issue of the European Journal of Nutrition.

"It is imperative to find natural, safe and effective alternatives for women to help maintain bone health after menopause -- without the risky side effects associated with long-term hormone replacement therapy use," Jocelyn Mathern, RD, technical specialist for Acatris, said in a news release. "This promising research is another step in advancing soy germ isoflavones as a safe, effective option."

This study, led by Y. B. Ye, MPhil, and Y. X. Su, MD, from Sun Yat-sen University in Guangzhou, China, examined the bone-sparing effect of high-dose isoflavones in Chinese early postmenopausal women. Previous studies showed that daily doses of 40 to 99 mg of soy isoflavones had inconsistent effects on preventing estrogen-related bone loss in postmenopausal women.

In this study, 90 women aged 45 to 60 years were randomized to receive daily dosages of 0 (placebo), 84, or 126 mg of isoflavones for 6 months. At baseline, body mass index was less than 30 kg/m 2, and Kuppermann Climacteric Scale was greater than 15. Outcomes included bone mineral density (BMD) of the spine and hip measured with dual-energy x-ray absorptiometry at 0 and 6 months; and serum osteocalcin, bone-specific alkaline phosphatase, and urinary deoxypyridinoline levels at 0, 3, and 6 months.

After adjustment for age, years since menopause, body weight, and height; dietary intakes of isoflavones, calcium, and protein; physical activities and baseline BMD and mean percent changes in BMD at the lumbar spine ( P = .114) and femoral neck ( P = .053) increased with supplementations of soy isoflavones. After adjustment, there was a significantly dose-dependent linear relationship between the supplemental isoflavones and percent changes of BMD at the spine ( P = .042) and femoral neck ( P = .016) after treatment, and urinary total deoxypyridinoline ( P = .014) at 12 weeks but not at 24 weeks. Percent changes in serum osteocalcin and bone-specific alkaline phosphatase levels were not significantly different among the 3 treatment groups at 12 and 24 weeks after treatment.

"There is a significantly dose-dependent effect of soy isoflavones on attenuating bone loss at the spine and femoral neck possibly via the inhibition of bone resorption in non-obese postmenopausal Chinese women with high Kuppermann Scale," the authors write. "The high dose of 126 mg isoflavones/d is an effective dose for the prevention of postmenopausal bone loss over a short duration."

Study limitations include short duration, lack of generalizability to obese postmenopausal women, and relatively small sample size.

"In addition to this research, more studies are examining the effects of either soy or isoflavones on bone density in humans," Dr. Mathern says. "We are awaiting results of a large study, the Osteoporosis Prevention Using Soy (OPUS) study, a multi-site, two year research study on the use of soy isoflavones to prevent bone loss in 400 postmenopausal women. Both this current study and OPUS used SoyLife, and we're excited to see SoyLife helping lead the way in determining the required dosage of soy isoflavones for safely decreasing bone loss and preventing osteoporosis in postmenopausal women."

Guangzhou Sciences and Technology Bureau and Acatris Holding B.V., the maker of SoyLife, supported this study. The soy isoflavone extract was donated by Acatris.

Eur J Nutr. Published online June 8, 2006.