The latest findings come from a study led by Giorgio Secreto, MD, director of the hormone research laboratory at Italy's National Cancer Institute. They analyzed data from 232 women treated for menopausal symptoms with either a soy extract (Soylife), melatonin, soy extract plus melatonin, or a placebo.
"Soy isoflavones improved menopausal symptoms in about 75% of women in the isoflavones alone group, a percentage not dissimilar to that observed in the placebo group," Secreto tells WebMD. "In particular, improvement of vasomotor symptoms [hot flashes] was observed in 74% of women treated with isoflavones versus 62.3% in the placebo group."
The difference between soy and placebo was not statistically significant. This means that the study did not find soy -- or melatonin -- to be particularly helpful.
The Secreto team's report appears in the January issue of the journal Maturitas. Accompanying it is a review of all major studies of soy for the treatment of menopausal symptoms. Study co-author Alyson L. Huntley, PhD, is a research fellow in complementary medicine at Peninsula Medical School, Universities of Exeter and Plymouth, Exeter, England.
"Soy phytoestrogens can have mild effects, and we think it is relatively safe for healthy menopausal women," Huntley tells WebMD. "I would say if you are suffering from severe hot flushes, you will see some effect using soy phytoestrogens. But it is not going to be a dramatic on-and-off effect. If women are suffering, it is worth trying."
Hormone replacement therapy continues to be the most effective treatment for menopausal symptoms. But many women -- and many doctors -- are reluctant to use it because at least some forms of HRT have been linked to increased cancer risk.
Secreto advises women to try soy and melatonin first.
"Women should know that soy isoflavones are less effective than HRT but much less dangerous," Secreto says. "They should also know, however, that the long-term effects of soy extracts are still largely unknown."
Thomas Clarkson, DVM, professor of comparative medicine at Wake Forest University School of Medicine in Winston-Salem, N.C., says the Secreto study adds to a growing list of trials showing soy has little or no effect on menopausal symptoms.
"The results of studies on soy and hot flashes suggest it has only a marginal or no benefit for hot flashes," Clarkson tells WebMD. "Women taking soy can expect to see 10% or 15% better results than if they took a placebo. Of course, these products cost a lot more than placebo, too."