Objective: This study aims to evaluate the associations of vasomotor symptom (VMS) frequency, bother, and severity with equol producer status and dietary daidzein intake.
Methods: This is an observational study. This study included women aged 45 to 55 years, in postmenopause or in the menopausal transition, who had soy food intake of three or more servings per week. Exclusion criteria included severe concurrent disease, pregnancy or planned pregnancy, and current use of oral or transdermal hormones or selective estrogen receptor modulators. After screening, 375 participants completed a 3-day VMS diary and a 24-hour urine collection. Women with a urine daidzein or genistein concentration of 100 ng/mL or higher were included. We evaluated the association of VMS—dichotomized as lower than or equal to versus higher than the mean number of VMS per day (<2.33, ≥2.33)—with quartiles of daidzein intake.
Results: Overall, 129 (35%) of 365 women were equol producers. The mean (SD) urinary equol excretion was 0.67 (1.57) mg/day (50th percentile, 0 mg/d; 95th percentile, 4.12 mg/d). Among equol producers, the mean (SD) urinary equol excretion was 1.91 (2.15) mg/day (50th percentile, 1.09 mg/d; 95th percentile, 6.27 mg/d). Among equol producers, compared with those in the lowest quartile of dietary daidzein intake (mean, 4.9 mg/d), those in the highest quartile (mean, 28.5 mg/d) were 76% less likely to have VMS higher than the mean number of VMS (odds ratio, 0.24; 95% CI, 0.07-0.83; trend test across all daidzein levels, P = 0.06). Among equol nonproducers, there were no associations between daidzein intake and VMS frequency. There were no differences in VMS bother or severity among equol producers or nonproducers by dietary daidzein level.
Conclusions: Among equol producers, higher equol availability attributable to higher soy consumption contributes to decreased VMS.
From the 1Group Health Research Institute, Seattle, WA; 2Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA; 3Department of Obstetrics and Gynecology, School of Medicine, University of Washington, Seattle, WA; 4Fred Hutchinson Cancer Research Center, Seattle, WA; 5Otsuka Pharmaceutical Co Ltd, Tokyo, Japan; and 6Pharmavite LLC, Mission Hills, CA.
Received March 10, 2014; revised and accepted September 3, 2014.
Funding/support: This study was supported by a research grant from Otsuka Pharmaceutical Co Ltd.
Financial disclosure/conflicts of interest: S.U. and T.U. are employees of and receive full salary from Otsuka Pharmaceutical Co Ltd, which is a sponsor of this study. S.I. is an employee of Pharmavite LLC, which is a subsidiary of Otsuka Pharmaceutical Co Ltd. S.I. receives salary support from Otsuka Pharmaceutical Co Ltd.
Address correspondence to: Katherine M. Newton, PhD, Group Health Research Institute, 1730 Minor Ave, Ste 1600, Seattle, WA 98191. E-mail: firstname.lastname@example.org