Does soy help cool hot flashes after all?

Despite a good amount of evidence to the contrary, a new research review suggests that soy supplements can indeed help women find relief from menopausal hot flashes.

So far, studies have come to conflicting findings on whether soy extracts are effective against the sudden bouts of feverish feeling experienced by many women transitioning to menopause.

Soy contains isoflavones, compounds that are thought to have weak estrogen-like effects in some body tissue. That hints that soy or soy extracts could help cool hot flashes. But whether that's actually the case has been unclear.

Last year, for example, a clinical trial of 248 women found no evidence that a soy isoflavone supplement worked better than placebo pills in easing menopausal symptoms. (See Reuters Health story of August 8, 2011.)

For the new study, researchers combined the results of 17 previously published clinical trials on the question.

Overall, they found, women who used soy isoflavone extracts had a 21 percent greater reduction in hot flashes compared with women given a placebo.

And when they did have hot flashes, they tended to be less severe.

The extent of the effects did vary among the different studies. But nearly all showed a "pattern" of soy isoflavones working better than a placebo, according to senior researcher Mark Messina, of Loma Linda University in California.

"I feel completely comfortable with recommending (soy isoflavones) to women who want to try them," said Messina, who also directs the Soy Nutrition Institute and regularly consults with companies that make soy products.

If you get no relief after about four weeks, Messina said, then it may be time to move on. A month's supply of soy supplements costs about $12.

The findings, reported in the journal Menopause, add to a generally conflicting body of research on what works for hot flashes.

The one consistently supported treatment is hormone replacement therapy (HRT), and right now, it's the only treatment specifically approved by the U.S. Food and Drug Administration for hot flashes.

But HRT is also linked to increased risks of blood clots, heart attack, stroke and breast cancer. So experts say hormones should be limited to more-severe cases of hot flashes, and that women use them at the lowest dose and for the shortest time possible.

Those safety concerns have meant that many women and doctors are looking for alternative hot flash relief.

A researcher not involved in the current study said it was "interesting" and "well done."

"I do think that soy isoflavones have a positive effect on hot flashes," said Kristi Kelley, an associate clinical professor at Auburn University Harrison School of Pharmacy in Birmingham, Alabama.