Many studies have demonstrated the effectiveness of isoflavones on menopausal symptoms; however, these mostly used high dosages. Because high-dose isoflavone may result in endometrial hyperplasia, we investigated whether low-dose isoflavone aglycone alleviates menopausal symptoms similarly to high dosages.

We conducted a randomized, double-blind, placebo-controlled study in 90 healthy women aged 40–60 years who had at least one menopausal symptom on the Menopausal Symptom Scale (MSS). The participants were randomized to receive active tablets containing ultralow-dose (12.5 mg/day; n = 30) or low-dose (25 mg/day; n = 30) isoflavone aglycone, or placebo (n = 30) tablets, for 8 weeks. Their menopausal symptoms were evaluated using MSS, Hospital Anxiety and Depression Scale (HADS), and Athens Insomnia Scale (AIS) before, and 4 and 8 weeks after treatment.

Eighty-seven women (97 %) completed the 8-week treatment. In the low-dose group, significant improvement was observed from baseline, in the following parameters: (1) HADS-depression subscale score, (2) AIS score, (3) MSS-somatic symptom score after 4 and 8 weeks of treatment, and (4) MSS-vasomotor symptom score after 8 weeks of treatment. The changes in scores on HADS-depression subscale and AIS from baseline to 8 weeks were significantly higher in the low-dose group than in the placebo group.

Low-dose (25 mg/day) isoflavone aglycone significantly alleviated symptoms of depression and insomnia in Japanese middle-aged women.

Clinical Trial Registration UMIN-CTR UMIN000011876.