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Another study reports soy ineffective for hot flashes relief

Robin Wulffson MD's picture
soy, phytoestrogen, hot flashes, night sweats, bone loss, prevention

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.

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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.

A previous study, published in the August 22 issue of the bimonthly journal Archives of Internal Medicine reported that soy isoflavones may not prevent menopausal symptoms or bone loss. The placebo-controlled, randomized, double-blind trial was conducted by researchers at the Miami Veterans Affairs Healthcare System and Miller School of Medicine. “Concerns regarding the risk of estrogen replacement have resulted in a significant increase in the use of soy products by menopausal women who, despite the lack of evidence of the efficacy of such products, seek alternatives to menopausal hormone therapy,” wrote Silvina Levis, MD and her colleagues. “Our goal was to determine the efficacy of soy isoflavone tablets in preventing bone loss and menopausal symptoms.” The women were 45 to 60 years old, within five years of menopause, and with a bone mineral density (BMD) T score of −2.0 or higher in the lumbar spine or total hip. From July 1, 2004, through March 31, 2009, a total of 248 subjects were randomly assigned to receive tablets containing soy isoflavone, 200 mg daily or placebo.

Outcomes were measured at a two-year follow-up. The main study endpoint was change in BMD in the lumbar spine, total hip, and femoral (thigh bone) neck, and secondary endpoints included changes in menopausal symptoms, vaginal cytologic (tissue) features, N-telopeptide of type I bone collagen, lipids, and thyroid function. The primary outcome was not significantly different between the two groups at two years. Changes in BMD in the spine in the subjects receiving soy tablets were −2.0% compared to −2.3% in those receiving placebo. BMD changes at the total hip were −1.2% for the soy group and −1.4% in the control group; percentages for the femoral neck were −2.2% for the soy group and −2.1% for the control group. Compared with the control group, the soy group had a significantly larger proportion of women who reported hot flashes (48.4% vs. 31.7%). Outcomes were otherwise similar in both groups. The authors concluded: “In this population, the daily administration of tablets containing 200 mg of soy isoflavones for two years did not prevent bone loss or menopausal symptoms.”

Reference: Menopause

See also:
Hormone replacement therapy use in US continues to decline
Tips to revitalize sex life after 50 with traditional Chinese medicine