Emerging research on equol and cancer

Area of Science:

• * Biochemistry and Molecular Biology
• * Oncology
• * Nutritional Science

Background:

• * In vitro studies suggest equol may influence cancer risk, but in vivo data are limited.
• * Equol is a gut bacterial metabolite of daidzein, an isoflavone found in soy.
• * Both S-(-)-equol and racemic equol have been investigated for their biological effects.

Purpose of the Study:

• * To review the current evidence on the role of equol in cancer risk.
• * To evaluate the impact of equol and its enantiomers on tumorigenesis and cancer biomarkers.
• * To identify gaps in knowledge and suggest future research directions.

Main Methods:

• * Review of in vitro studies on equol's mechanisms of action.
• * Analysis of rodent studies on equol's effects on mammary and skin carcinogenesis.
• * Examination of epidemiological studies on equol, isoflavones, and cancer risk in human populations.
• * Consideration of studies using intermediate biomarkers of cancer risk.

Main Results:

• * Rodent studies indicate equol does not stimulate mammary tumor growth but offers limited protection; it inhibits skin carcinogenesis in mice.
• * Epidemiological studies show no association or increased risk of breast cancer with equol in low-soy populations, but a trend toward decreased risk in Asian populations.
• * Population-based differences in equol's association with cancer risk are observed for both breast and prostate cancers, with Asian studies suggesting a protective role and European studies showing no association.
• * Studies on intermediate biomarkers yield varying results regarding the equol-producer phenotype and soy intake.

Conclusions:

• * The role of equol in cancer risk remains uncertain due to conflicting and limited evidence.
• * Further animal and human intervention studies using specific equol enantiomers (R- and S-equol) are necessary.
• * Investigating equol's effects on carcinogenesis and biomarkers will help clarify its impact on cancer risk.