1Division of Cancer Epidemilogy and Genetics, National Cancer Institute
2Division of Cancer Epidemiology and Genetics, National Cancer Institute
4Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health
Qian Xiao, Division of Cancer Epidemilogy and Genetics, National Cancer Institute, 9609 Medical Center Dr, Rockville, MD, 20892, United States
Experimental studies suggested that flavonoids may influence thyroid carcinogenesis, but epidemiological evidence is sparse. No study has examined different classes of flavonoids in relation to thyroid cancer risk. Using data from the NIH-AARP Diet and Health Study, which enrolled 491,840 U.S. men and women, ages 50 to 71 at baseline, we prospectively examined the risk of thyroid cancer in relation to dietary intakes of catechins, flavanones, flavonols, anthocyanidins, flavones, isoflavones, total flavonoids. Dietary intakes were assessed using a food frequency questionnaire. Cancer cases were ascertained by linkage to state cancer registries. Multivariable-adjusted Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).During follow up (mean=9 years), we identified 586 thyroid cancer cases. Thyroid cancer risk was inversely associated with dietary flavan-3-ols (HRQ5 vs Q1 (95% CI): 0.70 (0.55, 0.91), p-trend=0.03), but positively associated with flavanones (HRQ5 vs Q1 (95% CI): 1.50 (1.14, 1.96), p-trend=0.004). Other classes of flavonoids and total flavonoids were not associated with thyroid cancer risk. Similar associations were found for papillary thyroid cancer.Our findings suggest that dietary intake of different classes of dietary flavonoids may have divergent effects on thyroid cancer risk. More studies are needed to clarify a role of flavonoids in thyroid cancer development. Results from our study suggest a potential nutritional etiology of thyroid cancer.