Supplements containing a soy compound called genistein may help increase women's bone mass after menopause, a study suggests.
Italian researchers found that a combination of genistein, calcium and vitamin D helped protect postmenopausal women's bone density better than calcium and vitamin D alone.
In fact, women who took the soy compound showed a modest increase in bone density over two years, compared with a small decrease among women who used only calcium and vitamin D, the researchers report in the Annals of Internal Medicine.
Genistein is a type of isoflavone, plant chemicals that have effects similar to the female hormone estrogen and may have certain estrogen-like effects in humans. The estrogen decline that follows menopause contributes to bone density loss, and some research has linked high soy intake from food to a lower risk of the bone-thinning disease osteoporosis.
Mixed findings on effectiveness
However, studies on the effects of soy-based foods on bone mass after menopause have been inconsistent, said Dr. Francesco Squadrito, the senior author on the current study.
"This research is different in that it uses (a) nearly pure chemical from soy that you cannot obtain in sufficient quantities by simply eating more soy products," explained Squadrito, a researcher at the University of Messina in Italy.
Women in the study took 54 milligrams of genistein a day — an amount, Squadrito told Reuters Health, that's equivalent to 2 gallons of soy milk or about 8 pounds of tofu per day.
The study involved 389 postmenopausal women with lower than normal bone mass that had not yet progressed to osteoporosis. The women were randomly assigned to take either genistein or placebo (inactive) pills, every day for two years. Both the genistein and placebo pills also contained 500 mg of calcium and 400 IU of vitamin D.
After two years, bone scans showed that, on average, women who took genistein had gained some bone density in the hip and lower spine, while those in the placebo group had lost bone mass.
An important remaining question, however, is whether genistein actually prevents bone fractures over time.
In addition, a general concern with high doses of estrogen-like isoflavones is whether they might influence the risk of breast or uterine cancers.
Gastrointestinal side effects
In Squadrito's study women on genistein showed no thickening in the lining of the uterus, a sign of adverse hormonal effects. Instead, the main side effects were gastrointestinal problems like indigestion and constipation.
And Squadrito noted that, in general, genistein has shown an "exceptional safety profile" in studies.
Still, he urged some caution in using genistein supplements. "Because this molecule is in very high concentration compared to what you get in actual soy products," Squadrito said, "women should speak with their doctors regarding the use of any product containing high amounts of genistein."