Consumption of black tea elicits an increase in plasma antioxidant potential in humans

Abstract

Epidemiological studies suggest that the consumption of tea flavonoids may be associated with reduced risk of coronary heart disease, stroke and cancer-related deaths. The flavonoids are polyphenols which in vitro exhibit antioxidant properties. Tea flavonoids are known to be rapidly absorbed into the circulation following oral ingestion. To date few studies have demonstrated that these bioavailable flavonoids retain antioxidant properties in vivo. Nine healthy subjects aged between 26 and 59 (one male and eight females) took part in 3 study days. On 1 day subjects consumed no tea and on the other 2 days subjects drank either black tea with milk, or black tea alone at hourly intervals between 9.00 a.m. and 14.00 p.m. Blood was sampled at 9.00 a.m. and at 12.00 p.m. and 15.00 p.m. The antioxidant potential of plasma was determined using the ferric reducing antioxidant power (FRAP) assay. Subjects consuming no tea exhibited no significant change in FRAP across the 6 hours of the study day. Similarly consumption of milky tea produced no change in FRAP between 9.00 a.m. and 12.00 p.m. and the 50% increase in FRAP noted between 12.00 p.m. and 15.00 p.m. was not statistically significant. When the subjects consumed black tea without milk FRAP increased by 65% between 9.00 a.m. and 12.00 p.m. (P = 0.02) and at 15.00 p.m. was 76% higher than at 9.00 a.m. (P = 0.002). Heavy consumption of black tea thus appears to elevate circulating antioxidant potentials in vivo. This is an effect which appears to be totally negated by the drinking of tea with milk. Although tea may thus represent an important source of dietary antioxidants in many societies, the role of tea in reducing risk of major disease states needs to be investigated in more detail.