Longitudinal Associations of Total and Class-Specific Polyphenol Intake with Incident Type 2 Diabetes and Changes in Glycemic Markers: Findings from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) Cohort.

BackgroundThe prevalence of type 2 diabetes (T2D) is rapidly increasing worldwide, particularly in low- and middle-income countries, and can lead to severe health complications. Dietary polyphenols may help prevent T2D and support metabolic health.ObjectivesThis study aimed to investigate the longitudinal associations between dietary polyphenol intake and risk of incident T2D and changes in glycemic markers [fasting glucose, glycated hemoglobin (HbA1c), and homeostasis model assessment of insulin resistance (HOMA-IR)] in participants of the Brazilian Longitudinal Study of Adult Health.MethodsA total of 8781 participants (mean age 58.8 y, 61.3% female) free of diabetes at baseline were followed for a median of 7.6 y. Dietary polyphenol intake was assessed via a semiquantitative food frequency questionnaire at 2 time points, with polyphenol content estimated from the Phenol-Explorer database. Cox proportional hazards regression with time-varying exposure was used to assess associations between polyphenol intake tertiles and incident T2D. Linear regression models were used to examine associations with changes in glycemic markers between waves.ResultsDuring follow-up, 1453 incident T2D cases were identified. In the fully adjusted model, participants in the highest tertile of total polyphenol intake had a 19% lower risk of incident T2D than those in the lowest tertile (hazard ratio: 0.81; 95% confidence interval: 0.70, 0.93). Significant inverse associations were also observed for phenolic acids, hydroxycinnamic acids, total flavonoids, flavan-3-ol monomers, flavan-3-ol dimers to polymers, flavones, anthocyanins, and stilbenes, with risk reductions ranging from 13% to 27%. Participants in the highest tertile of total polyphenols, phenolic acids, and stilbenes showed significantly smaller increases in HOMA-IR over follow-up. No significant associations were observed for fasting glucose or HbA1c.ConclusionsHigher dietary polyphenol intake is inversely associated with incident T2D and attenuates insulin resistance progression over time. These findings support polyphenol-rich dietary patterns as a strategy for T2D risk reduction.