The researchers, led by Laurence Howes from Griffith University School of Medicine, pooled data from 17 randomised, controlled, parallel studies with a duration of at least four weeks studies identified from the Medline, Pre-Medline, PubMed and the Cochrane databases.
"This meta-analysis of the effects of isoflavone[s]… on the frequency of menopausal flushing found a statistically significant, although clinically modest effect, and that the extent of benefit appeared to be positively associated with the frequency of the flushes and possibly the dose of isoflavone used," wrote the authors in the Elsevier journal Maturitas.
"The results of the study tend to support the recommendation of the North American Menopause Society that "… for women with frequent hot flashes, clinicians may consider recommending soy foods or soy isoflavone supplements," they said.
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 appears to add weight to these claims. The analysis of Howe and colleagues reported that supplementation with isoflavone was associated with a significant reduction in the number of hot flushes, but the authors noted that there was significance variety amongst the studies analysed.
"The percentage reduction in flushes was significantly related to the number of baseline flushes per day and the dose of isoflavone studied," wrote the researchers.
Indeed, amongst women experiencing ten or more flushes everyday, the reviewers note that isoflavone supplementation was associated with a 20 per cent reduction in the number of flushes.
The results are at odds with another recent meta-analysis published in the Journal of the American Medical Association (Vol. 295, pp. 2057-2071), of six red clover isoflavone trials and 11 soy isoflavone trials, which reported no reduction in hot flushes.
"However, there were a number of key differences between this study and the one which we performed. Sources of isoflavones were considered as separate entities rather than contributors of a dose of isoflavone, end points other than frequency of flushing were also included, and (partly because of this reason), individual consideration of small groups of studies were made rather than a more comprehensive meta-analysis of therapies containing isoflavones," said Howes.
"The results of our study are therefore not necessarily incompatible with this recent systemic review."
The current study does have notable limitations, namely that changes in the severity of hot flushes was not considered, only changes in the number and frequency of the flushes. Also, the study did not measure the effect of isoflavones on other menopausal symptoms.
Demand for soy proteins and other products has been growing rapidly, driven largely by the research showing its health benefits. Market analysts The Freedonia Group predict that by 2007 US demand alone for soy products will rise by nearly five per cent each year to $8.23 (€6.7) bn.
Source: Maturitas Volume 55, Pages 203-211 "Isoflavone therapy for menopausal flushes: A systematic review and meta-analysis" Authors: L.G. Howes, J.B. Howes and D.C. Knight