Tea flavonols in cardiovascular disease and cancer epidemiology.

Tea is an important dietary source of flavonols in countries such as the Netherlands, the United Kingdom and Japan. Flavonols may have beneficial health effects because of their antioxidant properties and their inhibitory role in various stages of tumor development in animal studies. The association between flavonol intake and cancer risk was investigated in three prospective studies (Zutphen Elderly Study in the Netherlands, a Finnish cohort, and the Netherlands Cohort Study). Only one study (Finnish cohort) showed an inverse association with cancer mortality. The intake of flavonols with subsequent cardiovascular disease was studied in six prospective epidemiological studies. In some populations (Seven Countries Study, Zutphen Elderly Study, a Finnish cohort) a clear protective effect was observed. In a large US cohort, a protective effect was only found in a subgroup with previous history of coronary heart disease, whereas in Welsh men, flavonol intake, mainly from tea, was associated with an increased risk of coronary heart disease. These conflicting results may be due to confounding by coronary risk factors associated with tea consumption. The question of whether flavonols protect against cardiovascular disease remains still open; a protective effect of flavonols against cancer is less likely.