Soy may alleviate hot flashes in menopause, large-scale study finds

In the most comprehensive study to date to examine the effects of soy on menopause, researchers have found that two daily servings of soy can reduce the frequency and severity of hot flashes by up to 26 percent, compared to a placebo.

The findings, published in Menopause: The Journal of the North American Menopause Association, reviewed 19 previous studies that examined more than 1,200 women.

Although the effectiveness of soy in alleviating hot flashes has been inconclusive, with some studies suggesting soy to be beneficial and others suggesting otherwise, much of the discrepancy is due to small sample sizes and inconsistent methodology, according to the authors.

"When you combine them all, we've found the overall effect is still positive," said Melissa Melby, a medical anthropology professor at the University of Delaware and co-author of the study.

Examining the impact of soy isoflavones, chemicals found in soy that exert a mild estrogen-like effect, Melby and her colleagues found:

Ingesting at least 54 milligrams of soy isoflavones daily for six weeks to a year reduces menopause hot flash frequency by 20.6 percent and severity by 26 percent, compared to a placebo.
The total reduction in frequency and severity might be even greater due to the placebo effect.
In longer duration studies (where women consumed soy isoflavones for 12 weeks or more), the decrease in hot flash frequency was approximately threefold greater than in shorter-duration trials.
Isoflavone supplements with higher levels (at least 19 milligrams) of genistein, one of the two main types of isoflavones, were more than twice as effective at reducing hot flash frequency than lower amounts.

Melby called the genistein result particularly notable because the compound is the primary isoflavone in soybeans and soy foods, suggesting that, "Eating soy foods, or using supplements derived from whole soybeans, may work better for women."

Should menopausal women cross soy milk and tofu off their next grocery list?

Many menopausal women turn to soy to stave off nasty effects, like decreased bone density and hot flashes, because estrogen therapy is associated with risks for breast cancer and heart attack. But now researchers are calling for alternatives because a new study showed soy might not even work.

"Women should be reconsidering taking these types of products for menopausal health," Dr. Silvina Levis, lead author of the study and a professor of medicine at the University of Miami, told The New York Times.

For the study - published in the August 8 issue of Archives of Internal Medicine - researchers gave 126 women a placebo tablet and 122 women 200 mg of soy isoflavone tablets - twice the amount of soy found in a typical Asian diet, according to the researchers. The women, aged 45 to 60, were tracked for nearly five years to see if soy prevented bone loss and menopausal symptoms. At the end of the study, the researchers found no difference in bone loss between both groups. There was also no difference in the severity of night sweats, insomnia, vaginal dryness, and loss of libido - in fact, the women taking soy experienced more hot flashes and constipation.