To investigate the effect on hot flushes of a soy isoflavone extract alone (Study A) and with the addition of a supplement of polyunsaturated fatty acids, PUFAs (Study B).

Subjects were postmenopausal women (29 in Study A, 28 in Study B) with more than five troublesome hot flushes per day. Both studies were double-blind randomized placebo-controlled trials with cross-over design, of 24-week duration. After a 2-week observation period, they were randomized to receive two capsules per day providing 60mg of isoflavones or placebo for 12 weeks; thereafter, women who had taken isoflavones were given placebo for a second 12-week period, and vice-versa. Women in the Study B were given also two capsules per day containing a PUFA supplement for the entire 24-week test period.

Both studies showed the isoflavone extract to have no greater efficacy on hot flushes than the placebo. During the 24 weeks of the Study B there was a progressive and highly significant reduction in the number of hot flushes, independent of whether the women had begun with isoflavones or with placebo.

In these two trials the isoflavone extract did not show greater efficacy on the hot flushes than the placebo. The reduction of hot flushes observed in the Study B might be due to the PUFA supplement. PUFAs, particularly Omega (Omega) 3-fatty acids, could reduce hot flushes through their influence on neuronal membranes and/or the modulation of the neurotransmitter function and the serotoninergic system. Studies specifically designed to document the action of PUFAs on hot flushes would be welcome.