BACKGROUND: Our knowledge of the importance of flavonoid-rich foods in preventing unhealthy aging across its different domains is limited. OBJECTIVE: To examine prospective associations between flavonoid-rich food and flavonoid intakes and indicators of unhealthy aging, namely frailty, impaired physical function and poor mental health. METHODS: We followed 62,743 females and 23,687 males, all aged ≥60 years, from the Nurses' Health Study (1990-2014) and Health Professionals Follow-up Study (2006-2018), respectively. Both time-updated and change in intakes of a 'flavodiet' score (an aggregate of intakes of major flavonoid-rich foods and beverages) and individual flavonoid-rich foods and beverages and time-updated intakes of total flavonoids and flavonoid subclasses were calculated from food frequency questionnaires collected at baseline and every subsequent four years. Associations with incident frailty, impaired physical function and poor mental health, assessed from self-reported questionnaire responses, were examined with multivariable-adjusted Cox proportional hazards models. RESULTS: In the NHS, participants with the highest flavodiet scores, compared to the lowest, had a 15% lower risk of frailty [HR CONCLUSIONS: High intakes of flavonoid-rich foods may support healthy aging. Further research is needed, including examining sex-specific associations, as incorporating flavonoid-rich foods in the diet may be a simple strategy to support healthy aging.