The study, which was funded by a company that plans to manufacture supplements with the soy-based ingredient, called S-equol, showed that 24 percent more women who took the supplement had a decrease in hot flashes than women who did not take the supplement.
"Ask your pharmacist about natural treatments for menopause symptoms."
Dr. Takeshi Aso, of the Department of Obstetrics and Gynecology at Tokyo Medical and Dental University School of Medicine, and colleagues followed 160 post-menopausal Japanese women between the ages of 45 and 60 for three months.
The women were tested beforehand to be sure they do not naturally produce S-equol in their digestive systems, and they each experienced at least one hot flash each day.
All women in the study took a placebo for four weeks before the trial began to ensure they experienced hot flashes frequently enough to be included.
Women who took two 5mg S-equol supplements each day saw their flashes decrease by 59 percent, compared to 35 percent reduction seen among women who took a placebo.
Among women who had originally had at least three hot flashes daily, those who took the supplement experienced a 63 percent reduction in hot flash frequency, compared to the 24 percent decrease in placebo-taking women.
The severity of the hot flashes also decreased among women taking the S-equol supplement, based on a standard scale of menopause symptom severity that women used to record their daily symptoms.
Women taking the S-equol supplement also had less muscle stiffness in their necks and shoulders compared to those taking the placebo.
The ingredient in the supplement, called S-equol, can be produced naturally by the body in some people.
When specific bacteria in the digestive system metabolize daidzein, a compound found in soybeans, it produces S-equol.
If a person does not have that specific bacteria in their system or does not consume enough soy, S-equol will not be produced.
The study states that approximately 20 to 30 percent of North Americans and Europeans can produce high levels of S-equol.
About 50 percent of Asians produce S-equol, according to the study, probably because they tend to consume more soy than other groups.
The name of the supplement the women took was called SE5-OH, produced when researchers used bacteria to convert daidzein into S-equol, as the body would do during digestion.
Data on the safety of the supplement in the study showed no reported side effects. The researchers looked at the potential impact of SE5-OH on the women's sex, gonadal and thyroid hormones but found no adverse effects.
Previous studies involving SE5-OH have investigated its impact on breast and reproductive tissues and hormone levels and found no safety problems, according to the study.
The company that created the dietary supplement SE5-OH, Otsuka Pharmaceutical Co., Ltd., also paid for this study. Additional information about potential conflicts of interest of the researchers was not available.
The study appeared in the Journal of Women's Health. It was a randomized, double-blind, placebo-controlled study.