The analysis also revealed that soy isoflavones were effective in reducing the severity of hot flashes by about 26%.
“Soy isoflavones appear to be a good first approach to alleviating hot flashes. Since there is often a large placebo effect, women taking supplements with the right soy isoflavone profile will likely see at least a 50 percent reduction compared to doing nothing,” said study co-author Melissa Melby, PhD, from the University of Delaware.
Isoflavones are well known phytoestrogens - active substances derived from plants that have a weak estrogen-like action.
Isoflavones from soy have been shown to provide a number of health benefits, including the promotion of heart health and the maintenance of bone health in post-menopausal women.
They have also been studied for their role in cancer prevention and slowing down the ageing process in peri-menopausal women, and have proved to be a popular alternative to hormone replacement therapy for those wishing to control menopause symptoms without resorting to drugs.
The new meta-analysis provides strong support for the efficacy of soy isoflavones to reduce the frequency and severity of hot flashes.
Scientists from the Japanese National Institutes of Health, the University of Delaware, Stanford University, the University of Minnesota, and an industry consultant identified 19 trials for their systematic review and 17 for their meta-analysis.
The analysis revealed that an average intake of 54 milligrams per day of soy isoflavones for between 6 weeks and 12 months was associated with an average 21% reduction in the frequency of hot flashes, compared with placebo.
In addition, this dose and duration was associated with a reduction in the severity of hot flashes by 26%, compared with placebo.
In terms of the specific isoflavones, supplements that provided at least 18.8 mg of genistein “were more than twice as potent at reducing hot flash frequency than lower genistein supplements”, said the reviewers.
“Supplements providing a total of 50 mg of total isoflavones will be effective as long as they also provide at least 19 milligrams of genistein,” said Mark Messina, PhD, industry consultant and co-author to the study.
The study was welcomed by Steve O’Brien, product manager of natural health and nutrition at soy supplier.
“We are pleased that such a thorough evaluation of the most well-conducted studies showed that soy isoflavones are highly effective for the alleviation of hot flashes,” he said.
Published online ahead of print, doi: 10.1097/gme.0b013e3182410159
“Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials”
Authors: K. Taku, M.K. Melby, F. Kronenberg, M.S. Kurzer, M. Messina