Another study reports soy ineffective for hot flashes relief
Soy contains isoflavones, which act as phytoestrogens (estrogen-like substances) in mammals. Some researchers have suggested that the isoflavones in soy might provide relief from the troublesome menopausal symptoms: hot flashes and night sweats. A new study supports findings of a previous study that soy is ineffective in providing either relief of hot flashes or prevention of bone loss.
Researchers affiliated with the University of California, Davis published their findings on October 31 in the journal Menopause. It will appear in the print edition of the March 2013 issue of the journal.
The researchers noted that a reduction of vasomotor symptoms (hot flashes and night sweats) has been reported in postmenopausal women who ingested soy; however, these studies did not report a clear dose response for perimenopausal women. They added that these studies primarily reported a reduction in already present vasomotor symptoms and did not note a prevention of developing these symptoms. Therefore, the investigators analyzed longitudinal data from the Study of Women's Health Across the Nation for the relation of dietary phytoestrogen and fiber intake to incident vasomotor symptoms in this multiracial/ethnic cohort.
The Study of Women's Health Across the Nation included 3,302 premenopausal and early perimenopausal women; 1,651 of these women reported no vasomotor symptoms at baseline and were followed with annual visits for 10 years. They conducted a placebo-controlled, randomized, double-blind trial. (Placebo-controlled means that half the subjects received a placebo; randomized means the subjects were randomly assigned to receive soy or a placebo; and double-blind means that neither the subjects or the researchers knew which patients were receiving soy.) Dietary intakes of isoflavones, coumestrol, lignans, and fiber were assessed by a food frequency questionnaire at baseline and in annual visits 5 and 9 and interpolated for intervening years. The number of days, the women experienced vasomotor symptoms in the past two weeks was self-reported annually. The researchers evaluated vasomotor symptoms in relation to isoflavones, lignans, fiber, coumestrol, or total phytoestrogen intake and covariates.
The others found no consistent relationship between any dietary phytoestrogen or fiber and vasomotor symptoms; however, “adjusted odds ratios for some individual quartiles were statistically significant.” The authors concluded that for certainty of any effect of dietary phytoestrogens or fiber on the prevention of incident vasomotor symptoms, a randomized, placebo-controlled, double-blind trial with sufficient numbers of women in different racial/ethnic, menopausal status, and metabolic groups over years of follow-up is required. They added that their results suggested that a clinically significant or large effect is improbable.