S-Equol for Hot Flashes: What the Trials Selected and Measured

S-equol is a metabolite of the soy isoflavone daidzein. A supplement can provide it directly. That makes the research question different from whether eating soy foods reduces hot flashes.¹

The Japanese trial selected equol nonproducers

The placebo-controlled trial published in 2012 randomized 160 women, aged 45–60, after menopause. All were Japanese equol nonproducers, identified through testing after a soy challenge. They received 10 milligrams daily of S-equol as SE5-OH or placebo for 12 weeks.²

During a preceding four-week placebo screening period, women with a 50% or greater improvement in the overall menopausal symptom index were excluded. The later trial therefore concerned a group already screened for a substantial placebo response.²

The efficacy analysis included 126 women, omitting 34 randomized participants. Average hot-flash frequency fell by 1.9 per day with S-equol and 1.0 with placebo, a significant difference. The additional average reduction was about 0.9 per day.²

Otsuka supplied the product and financial support; two authors reported consulting fees from the company. These details, the selected population and the incomplete analysis belong beside the favorable result.²

The other 2012 trial compared S-equol with soy

An eight-week pilot randomized 102 women aged 45–65, after menopause and experiencing at least five hot flashes daily. Its four groups received 10, 20 or 40 milligrams of S-equol daily, or soy isoflavones. There was no placebo group.¹

According to the original published abstract, reductions at week 8 were similar across groups. A separate analysis of the cumulative eight-week effect favored 40 milligrams over isoflavones. Higher-dose findings also appeared in a subgroup with more than eight daily flashes at baseline.¹

Those are different analyses. A favorable cumulative or subgroup finding should not be presented as superiority on every outcome, and comparison with soy cannot establish how much improvement would have occurred with placebo. The pilot does not justify increasing a supplement dose yourself.

The review was encouraging, with different interventions included

The published abstract of a 2019 systematic review reported six studies involving 779 participants; five studies with 728 participants entered its meta-analysis. Three reported significant benefit and two did not. The pooled result favored equol for hot-flash scores.³

Its eligibility criteria included both equol itself and soy isoflavones given to equol producers. That matters when a supplement advertisement presents the total as if every participant took the same S-equol product. We could read the review’s abstract, rather than its full analysis.³

Why the Society does not recommend it

The 2023 nonhormone position statement considered the positive review and still placed equol in its not-recommended group, with Level II evidence indicating limited or inconsistent findings. It noted that four of six studies had fewer than 50 participants per group.⁴

The statement also explains that equol binds estrogen receptors. A supplement label should not be treated as an assurance that the ingredient has no estrogen-related biological activity or is suitable for someone avoiding estrogen effects. Discuss that question with your clinician, especially when choosing treatment after cancer.⁴

The Society’s current patient page continues to list S-equol among approaches with limited supporting data or unsuccessful trial results. For disruptive flashes, it describes hormone therapy, nonhormone prescription treatments, cognitive behavioral therapy and clinical hypnosis as options to discuss.⁵

Bring a daily flash count, nights interrupted and the supplement label. Ask which treatment has evidence for your symptom burden and health history. A study’s average reduction can help frame that conversation; it cannot predict your response.

Chapter 5 of My Body Changed. Now What?, “The Heat,” includes “The Supplement Shelf,” comparing plant-product evidence and explaining why a placebo comparison matters.