THURSDAY, Nov. 22 (HealthDay News) -- Consuming soy products doesn't prevent hot flashes and night sweats in most women, a large study suggests.

Imagine sitting down for a job interview and suddenly feeling very warm and starting to noticeably perspire. Or consider how it feels to frequently lose sleep from drenching night sweats. Of all the symptoms of menopause, women say hot flashes and night sweats often are the most annoying.

The symptoms are caused by fluctuating or decreasing levels of the female hormone estrogen.

Many women are not willing or able to take supplemental estrogen to control hot flashes and night sweats, known as "vasomotor" symptoms, related to widening and narrowing of blood vessels. Some women opt to add dietary soy products like tofu and soy milk to their diet. Also called phytoestrogens, they have a chemical structure similar to estrogen and are thought to mimic the effect of the female hormone in the body.

The study was published online recently and will appear in the March 2013 print issue of the journal Menopause.

"We were interested in finding ways to help women control their own health, and we were hopeful that soy products would prove to be a good alternative to hormone therapy," said lead study author Ellen Gold, professor and chairwoman of the department of public health sciences at the University of California, Davis. Unfortunately, she said, soy "doesn't seem, on average, to prevent these unpleasant symptoms before the onset of menopause."

The study analyzed data from a nationwide study that followed more than 3,000 women who were beginning to experience changes associated with menopause or had not yet begun to have symptoms of menopause. Their ages ranged from 42 to 52 years old at the start of the study.

Participants answered detailed surveys about their dietary habits and fiber intake before they were involved in the study, then at five- and nine-year follow-up points. Fiber was of interest to the researchers because it is thought to increase the impact of estrogen. The women also were asked annually about their menopausal symptoms, including hot flashes and night sweats.

The study found no significant correlation between the intake of dietary phytoestrogens or fiber and the beginning of menopausal symptoms in women who had not yet experienced menopause when they started the study.

Gold said that a randomized, placebo-controlled trial with a diverse range of women would be necessary to prove any ability of dietary phytoestrogens or fiber to prevent hot flashes and night sweats, but she believes the results of this study suggest that it is unlikely a significant effect would be seen.

Although other studies have looked at dietary soy and menopausal symptoms, this study included more women and followed them for a longer period of time than others did, the researchers said. The study also included people representing a broader range of racial and ethnic groups, including black, Hispanic, Chinese and Japanese women.

Although Asian women tend to report fewer vasomotor symptoms than other women, the typical Eastern diet, thought to be high in phytoestrogens, does not seem to be associated with fewer hot flashes and night sweats.

Gold said she believes there may be subsets of women, due to genetic and metabolic factors, who may benefit more from phytoestrogens than others. And she doesn't discourage women from taking soy products. "If women try it and it works for them, fine," she said.

The study has some limitations.

Dr. Wilma Larsen, chief of the division of gynecology at Scott & White Healthcare in Temple, Texas, is concerned that the study used data the women had written down or remembered.

"Any time you're relying on patients to self-report you're not certain what they're actually doing," Larsen said.

Although Larsen said the study contributes new information specifically about whether soy products are helpful in preventing hot flashes and night sweats before they occur, she doesn't think it will change what women do or what physicians recommend.

"I think this isn't going to prevent me from talking about a healthy diet with patients or the value of phytoestrogens," Larsen said. "And I'm certainly not going to be reassuring women that they'll go through menopause without having to take any prescription medicines."

The study was supported in part by the U.S. National Institutes of Health.

More information

Visit the U.S. Centers for Disease Control and Prevention to learn more about menopause.

SOURCES: Ellen Gold, Ph.D., professor and chairwoman, department of public health sciences, University of California, Davis; Wilma Larsen, M.D., chief, division of gynecology, Scott & White Healthcare, and associate professor, Texas A&M Health Sciences Center College of Medicine, Temple, Texas; Oct. 23, 2012, Menopause online

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