Soy supplements do not have the capability to ease the symptoms of menopause or protect against bone loss in women, researchers have found.
In their two year study they found that there were no differences in changes in bone density or menopausal symptoms between women taking soy and those taking a placebo, although women taking isoflavones did have more hot flashes, Dr. Silvina Levis of the University of Miami and colleagues reported in the August 8/22 issue of Archives of Internal Medicine. During menopause a woman's body produces less estrogen and progesterone. Hormone therapy, which entails replacing one or both of these hormones via medications, significantly reduces menopausal symptoms and helps maintain bone health, but it can also increase the risk of blood clots, stroke, heart disease and breast cancer.
The Women's Health Initiative earlier tied hormone replacement therapy to several adverse effects, particularly cardiovascular disease thus egging researchers to look elsewhere for treatments for menopausal symptoms. Many have turned to soy, which contains phytoestrogens, specifically the isolflavones genistein and daidzein, the researchers wrote. Studies have shown a lower prevalence of osteoporotic fractures, breast cancer, and cardiovascular disease in Asian women, which has been largely attributed to their soy-rich diets. Yet prior evidence for the efficacy of soy supplementation has been limited by poor study design, small sample size, and short duration of treatment.
Thus this study called the Soy Phytoestrogens As Replacement Estrogen (SPARE) study was conducted as a single-center randomized, controlled, double-blind trial, in 248 women, ages 45 to 60, between July 1, 2004 and March 31, 2009. All of the women were within five years of the start of menopause, and had a bone mineral density score of -2.0 or higher at the lumbar spine or total hip. They were randomized to placebo, or to 200 mg daily of soy isoflavone tablets. After two years, the researchers found no significant differences in any measurements of bone mineral density between those on soy versus those on placebo. The team also controlled for other factors except with regard to vitamin D status. Women whose levels were below 20 ng/mL in the placebo group had a significantly greater decrease in spinal bone density than those taking soy. On the flip side the researchers found that significantly more women taking soy supplements had hot flashes. There were no differences in vaginal cytologic characteristics or cholesterol, triglycerides, or thyrotropin levels between groups, they reported.
There were no differences between the groups in adverse effects, except those on soy reported more constipation, a finding of marginal significance. Overall, there were 12 serious adverse events - nine in the soy group and three in the placebo group. Seven women in the soy group reported fractures compared with just one on placebo. All these fractures were associated with a traumatic event and not considered to be osteoporotic fractures, the researchers noted.
It was noted that more in the placebo group dropped out ((34.1 percent versus 18.8 percent), but Levis and colleagues said the numbers don't necessarily indicate favorable effects for soy because there was no objective documentation of a benefit.
In an invited commentary, Katherine Newton of Group Health in Seattle and Dr. Deborah Grady of the University of California San Francisco wrote that questions still remain as to whether soy may have benefits in specific groups. A metabolic product of daidzein known as equol is thought to be more biologically active than daidzein, but only 25 percent to 50 percent of women metabolize daidzein into equol she explained. Though the study found no enhanced effects for equol producers, Newton and Grady said this metabolite should have been measured immediately after daidzein ingestion in order to accurately assess equol producer status. Thus, these findings may require further investigation, they wrote.
In general, they said, efforts may need to move “away from the hope of a one-size-fits-all therapy for menopausal symptoms towards using existing treatments to target the symptoms that disturb patients most,” adding that non-hormonal therapies, such as selective serotonin reuptake inhibitors and gabapentin, may be effective treatments.
Experts had mixed reactions to the study's findings. “This study, I think, is pretty much where the story ends for isoflavones and bone,” says Mark Messina. Messina is an adjunct associate professor at Loma Linda University and an expert consultant for the United Soybean Board. Messina points to another study published in 2010 in the Journal of Clinical Nutrition. That study tested similar doses of soy against a placebo in 224 early menopausal women. It also concluded that soy offered little protection against bone loss, which accelerates for most women in the first few years after menopause. “These studies make it very difficult to promote this idea that isoflavone supplements, at least, are good for bone health,” Messina says. But he thinks the study's finding that soy didn't help hot flashes and possibly made them worse was wrong.
Messina added that he recently reviewed 19 studies of soy for hot flashes. The results of his review, which were presented at a medical conference, found a clear reduction in the frequency and severity of hot flashes. Compared to placebo, the use of soy resulted in about a 50% reduction.
Another analysis of 19 studies also found a benefit in soy supplements for hot flashes. The benefit, though, was very slight. That review, which was published in the journal Menopause in 2010, found that on average, soy supplements cut the number of daily hot flashes women had by less than half a single hot flash.
“I agree that soy probably doesn't cause hot flashes, If it works….it's a tiny effect and probably not worth taking great big amounts of soy,” Grady said.