Associations of Dietary Flavonoids with Risk of Type 2 Diabetes, and Markers of Insulin Resistance and Systemic Inflammation in Women: A Prospective Study and Cross-Sectional Analysis

OBJECTIVE: Flavonoids, as antioxidants, may prevent the progressive impairment of pancreatic beta-cell function due to oxidative stress and may thus reduce the occurrence of type 2 diabetes. The aim of the present study was to examine the association of dietary flavonol and flavone intake with type 2 diabetes, and biomarkers of insulin resistance and systemic inflammation. METHODS: In 38,018 women aged > or =45 y and free of cardiovascular disease, cancer and diabetes with an average 8.8 y of follow-up, we calculated relative risks (RRs) of incident type 2 diabetes (1,614 events) according to dietary intake of total or individual flavonols and flavones and flavonoid-rich foods. We also measured and examined plasma concentrations of insulin, HbA(1C), CRP, and IL-6 in relation to total flavonol and flavone intake among 344 nondiabetic women. RESULTS: During 332,905 person-years of follow-up, none of total flavonols and flavones, quercetin, kaempferol, myricetin, apigenin, and luteolin was significantly associated with risk of type 2 diabetes. Among flavonoid-rich foods, apple and tea consumption was associated with diabetes risk. Women consuming > or =1 apple/d showed a significant 28% reduced risk of type 2 diabetes compared with those who consumed no apples (the multivariate-adjusted RR = 0.72, 95% CI: 0.56, 0.92; p = 0.006 for trend). Tea consumption was also inversely associated with diabetes risk but with a borderline significant trend (> or =4 cups/d vs. none: RR 0.73, 95% CI: 0.52-1.01; p for trend = 0.06). In 344 nondiabetic women, total intake of flavonols and flavones was not significantly related to plasma concentrations of fasting insulin, HbA(1C), CRP, or IL-6. CONCLUSIONS: These results do not support the hypothesis that high intake of flavonols and flavones reduces the development of type 2 diabetes, although we cannot rule out a modest inverse association with intake of apples and tea.