Dietary polyphenol intake in the prevention and management of diabetes mellitus: a systematic review of observational studies.

Diabetes mellitus (DM) is a major clinical and public health concern because of its high population burden. Clinical trials report promising antidiabetic effects of dietary polyphenols using supplementation. This systematic review investigated habitual-level polyphenol intake associations in observational studies for pre-, type 1, type 2, and gestational DM prevention and management. This review aimed to evaluate whether these associations may have implications for public health nutrition guidance. Database searches were last conducted in January 2025. Only articles available in English were considered. We identified 32,662 articles, of which 53 studies met the eligibility criteria and were included in the review. We used The Risk of Bias In Non-Randomized Studies-of Exposure (ROBINS-E) tool to assess risk of bias. Measures of association for each type of DM (primarily pre-DM and T2DM) were evaluated and synthesized. Strengths of associations between each polyphenol class and DM outcomes varied; however, flavonoids and lignans had repeated small to moderate DM risk reduction. Our findings suggest that higher habitual intake of polyphenol-rich foods may be associated with DM prevention, but the strength of evidence is not sufficient to justify dietary recommendations. T1DM and GDM were underrepresented in our review, warranting future investigations (PROSPERO registration #CRD420251003017).