Red clover extracts marketed to treat menopause symptoms had no significant effect on hot flushes, reported researchers in this week's Journal of the American Medical Association.
The study compared the effects of placebo with the products Promensil (82mg of total isoflavones per day) and Rimostil (57mg of total isoflavones per day) in a group of 250 menopausal women, who had at least 35 hot flushes each week.
After follow-up for 12 weeks, both supplement groups and the placebo group saw the same reduction in number of hot flushes. However participants in the Promensil group had less hot flushes sooner than other groups, reported the team.
Quality-of-life improvements and adverse events were also the same in the three groups.
The results challenge the positive findings of a study published last year, which found that 40mg of Promensil daily reduced hot flushes by nearly 50 per cent.
Dietary supplements containing isoflavones, such as those found in red clover or soy, are widely used as alternatives to hormonal therapies for hot flushes, especially since research found increased risk of cardiovascular disease and breast cancer among women using hormone replacement therapy.
Data on the efficacy of isoflavones is however inconclusive. A recent report suggested that the natural chemicals may work best on initial hot flushes.
At the same time, the manufacturer of the supplements, Australian firm Novogen, issued information on a study showing Promensil to help alleviate vaginal dryness in menopausal women.
A double-blind, placebo controlled trial by King's College Hospital London, found Promensil to minimise the condition, experienced by around half of menopausal women.
Dr Whitehead, director of the Gynaecology / Endocrinology Unit, King's College Hospital London, said: "Unlike steroidal oestrogens, the natural isoflavone phytoestrogens or plant oestrogens provided by the red clover supplement are showing a selective oestrogen receptor modulator (SERM)-like effect i.e. giving a welcome oestrogenic effect in relieving vaginal dryness while showing no adverse thickening effect on the endometrium."