Taking soy isoflavones supplements is associated with a reduction in the frequency and severity of hot flashes, according to a new study from the University of Minnesota and other research institutions.
If this finding holds, it would be good news for many women. Hot flashes — and their uncomfortable cousin, night sweats — are the key complaints of women going through menopause. So far, the only sure relief for hot flashes and night sweats is hormone therapy, which has been linked to an increased risk of breast cancer and other serious health problems.
Soy has also been linked to breast cancer, but that research is highly controversial, and most experts seem to agree that in moderation, at least, soy poses few health hazards.
The U of M study, which was published this week in the journal Menopause, pooled data from 19 previous studies involving about 1,200 women from 10 countries. (Such studies are known as meta-analyses.) Only studies that used soy supplements (rather than soy foods) were included because the amount of isoflavones being consumed was better controlled.
An analysis of that data found that women who took at least 54 milligrams of supplemental soy isoflavones daily for six weeks to a year reported a 21 percent decrease in the frequency and a 26 percent decrease in the severity of their hot flashes.
This symptom improvement was on top of the placebo effect, which has been shown to also reduce the frequency and severity of hot flashes — by up to 30 percent, according to some research.
“Our overall conclusion was that soy isoflavones do in fact have a significant effect,” said Mindy Kurzer, a co-author of the study and director of the Healthy Foods, Healthy Lives Institute at the University of Minnesota, in a phone interview Wednesday.
Kurzer also serves as a scientific advisor to the Soy Nutrition Institute, an industry-funded group that promotes soy foods and products. This current study, however, was not funded with industry money, she said.
Previous research inconclusive
The idea that soy may help relieve hot flashes stems from observational studies that have shown that women in Japan are much less likely to complain of hot flashes than women in North America. But past studies that have looked directly at the effect of soy foods or soy supplements on hot flashes have been inconclusive.
One well-designed randomized controlled trial published in 2011, for example, found that women who took 200 milligrams of soy isoflavones for two years reported no fewer hot flashes than women who took a placebo. In fact, the women in that study who were taking the soy isoflavones reported more constipation, bloating and hot flashes than those on the placebo pills.
That study was too recent to be included in the new meta-analysis, which only looked at studies published through December 2010. The 19 studies included in the meta-analysis varied widely in their methodologies and in the soy supplements used, but Kerzer said she’s confident that the reduction in the severity and frequency of hot flashes that she and her colleagues found is real.
“The statistics we did in this study were very, very sophisticated,” she said. “The fact that we were able to find a significant effect despite the variability in the studies suggests to me that the finding was certainly true and possibly the real effect was even greater,” she added.
Food may be preferable
Although the meta-analysis only included soy supplements, Kerzer said that eating two helpings daily of soy food — say, two glasses of soymilk or seven ounces of tofu — might offer women a more preferable way of consuming the isoflavones.
That amount of soy food should not pose any health risks for most women, she added.
“Soy has been consumed in Asia for hundreds and thousands of years, so the likelihood of the risks is probably very low,” she said.
The other authors of the meta-analysis are from Loma Linda University, Stanford University, the University of Delaware and Japan's National Institute of Health and Nutrition.