MONDAY, Aug. 8, 2011 (HealthDay News) -- Soy supplements, sometimes promoted as a healthier alternative to estrogen for maintaining bone and relieving menopausal symptoms, don't appear to do so, according to a new study.
"Our study shows that contrary to popular belief, soy isoflavone supplements do not prevent bone loss or alleviate menopausal symptoms," said lead author Dr. Silvina Levis, professor of medicine and director of the Osteoporosis Center at the University of Miami Miller School of Medicine.
In fact, a greater percent of women taking the supplements had hot flashes after the study than those taking the placebo.
The study, funded by the U.S. National Institutes of Health, is published Aug.8 in the Archives of Internal Medicine. The researchers reported no conflicts of interest.
Levis and her colleagues evaluated 248 women between the ages of 45 to 60, all of whom were menopausal. At the study start, they had bone density levels considered healthy.
In a study in which neither the participants nor the researchers knew which women were getting what, the team randomly assigned 126 volunteers to the placebo group and 122 to the soy group. The latter group took 200 milligrams of soy isoflavones a day for two years.
After two years, the researchers measured the hip and spine -- standard areas to screen for bone loss -- to determine whether the soy had made a difference in bone density. It had not.
They also looked at the women's reports of menopausal symptoms. At the beginning, 176 of the women reported one or more symptoms such as hot flashes, night sweats, insomnia, loss of libido or vaginal dryness.
The two groups showed no differences in any of the symptoms at the end of the study, except hot flashes: Those taking soy isoflavone supplements actually had more. Of those taking soy supplements, more than 48 percent had hot flashes, compared to about 32 percent of those on placebo.
More women taking soy isoflavone tablets reported constipation, too, although the differences were not significant from a statistical point of view.
The researchers did find that spinal bone loss was smaller in a subgroup of women taking the soy isoflavone tablets: women whose vitamin D levels were less than 20 nanograms per milliliter.
Interest in soy supplements increased after the Women's Health Initiative study, halted in 2002, found increased risk of strokes and heart attacks in women who took combination hormone therapy using estrogen and progesterone. Soy has been promoted as an alternative to estrogen, providing comparable benefits of bone preservation and symptom relief without the risks.
Levis said that if a patient were to ask her now about taking soy for menopausal symptoms or bone health, "I would not suggest they start for hot flash [relief] or bone loss prevention."
Dr. Deborah Grady, professor of medicine and epidemiology at the University of California San Francisco, co-wrote a commentary to accompany the study. In an interview, she said that, "I personally would say we have spent enough time and effort on this. And to do more trials on soy doesn't seem to be an efficient way to spend money if we want to come up with better treatments for menopausal women."
Many studies have looked at soy, she said. Every time one has had negative results, it seems, people say perhaps the dose was wrong or perhaps the study was not long enough, she noted.
But the results of the new study are definitive, Grady said. "This one is important because it was funded by the NIH, was long-term and they gave a huge dose of soy."
The bottom line: "Paying money to buy soy supplements doesn't make sense," she said.
Costs vary, but soy isoflavone supplements are widely sold on the internet. A month's supply can be bought for about $7.
Grady points out that the study was on soy supplements only; in addition, the study found the soy supplements to be benign. "It probably is not going to hurt anyone to eat soy in their diets," she said.
In her commentary, Grady also noted that the search for a safe alternative to hormone replacement therapy continues, with some menopausal women finding their symptoms are relieved by the class of antidepressants known as SSRIs. Other researchers have recommended yoga and other relaxation techniques as complementary therapies.
"Perhaps effort should be directed away from the hope of a one-size-fits all therapy for menopausal symptoms toward using existing treatments to target the symptoms that disturb patients most," Grady and her co-author concluded in the journal.
To learn more about alternative options for menopausal symptoms, visit the U.S. National Institutes of Health.