Association of Urinary Equol Concentration with Frailty in Community-Dwelling Older Adults: The Itabashi Longitudinal Study on Aging

BACKGROUND: Frailty is a common geriatric syndrome associated with adverse health outcomes. Equol, a metabolite of the soy isoflavone daidzein, has gained attention for its potential health benefits, particularly in bone, muscle, and cardiovascular health. This study examines the association between urinary equol concentration and frailty status in older adults, with participants further classified into equol producers and non-producers. METHODS: A cross-sectional analysis was conducted using data from 651 community-dwelling older adults (aged 70-85) participating in the Itabashi Longitudinal Study on Aging in February 2023. Urinary equol concentration was measured using Enzyme-Linked Immunosorbent Assay, and participants were classified as equol producers (≥1,000 nmol/L) or non-producers (<1,000 nmol/L). Frailty was assessed based on the revised Japanese Cardiovascular Health Study criteria. Binomial logistic regression was used to evaluate the association between equol production and frailty status or its components, adjusting for age and sex. RESULTS: Of the participants, 57.1% were equol producers. Fifty-five point eight percent were categorized as frail or prefrail. Equol producers had a significantly lower odds ratio (OR) for frailty or prefrailty (OR=0.71; 95% CI, 0.51-0.97) compared to non-producers. Among the frailty components, low physical activity was associated with equol production (OR=0.60; 95% CI, 0.41-0.88). CONCLUSION: Equol production was inversely associated with the prevalence of frailty or prefrailty, particularly with respect to maintaining physical activity. This suggests a potential protective role of equol-producing capacity in healthy aging, warranting longitudinal studies to further explore this association.