Dietary flavonoid intake and colorectal cancer: a case-control study.

Diets rich in flavonoids may reduce the risk of developing colorectal cancer. Flavonoids are widely distributed in foods of plant origin, though in the UK tea is the main dietary source. Our objective was to evaluate any independent associations of total dietary and non-tea intake of four flavonoid subclasses and the risk of developing colorectal cancer in a tea-drinking population with a high colorectal cancer incidence. A population-based case-control study (264 cases with histologically confirmed incident colorectal cancer and 408 controls) was carried out. Dietary data gathered by FFQ were used to calculate flavonoid intake. Adjusted OR and 95 % CI were estimated by logistic regression. No linear association between risk of developing colorectal cancer and total dietary flavonol, procyanidin, flavon-3-ol or flavanone intakes was found, but non-tea flavonol intake was inversely associated with colorectal cancer risk (OR 0.6; 95 % CI 0.4, 1.0). Stratification by site of cancer and assessment of individual flavonols showed a reduced risk of developing colon but not rectal cancer with increasing non-tea quercetin intake (OR 0.5; 95 % CI 0.3, 0.8; P(trend) < 0.01). We concluded that flavonols, specifically quercetin, obtained from non-tea components of the diet may be linked with reduced risk of developing colon cancer.