Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/21/2001
Publication Date: 6/1/2001
Citation: Warden, B.A., Smith, L.S., Beecher, G.R., Balentine, D.A., Clevidence, B.A. 2001. A balance study of the prominent polyphenolies in black tea. American Journal of Clinical Nutrition. 131(6):1731-7. Interpretive Summary: Some, but not all, studies of populations have suggested that flavonoids, natural compounds in fruits and vegetables, protect against cancer and heart disease. In linking flavonoids with protection from disease, it would be useful to understand the degree to which these phytonutrients are absorbed and thus available for cells to use. This study investigated the ability of human subjects to absorb catechins, a family of flavonoids, from regular (black) tea, and also measured excretion of these compounds in urine and feces. After eating a diet low in flavonoids for 5 days, subjects drank black tea 4 times over 6 hrs. Samples of blood, urine and feces were collected over 24-72 hr, and amounts of the 4 catechins were measured. The catechins studied were epigallocatechin, EGC; epicatechin, EC; epigallocatechin gallate, EGCG and epicatechin gallate, ECG. Catechins in plasma, urine and feces increased in response to tea consumption. Yet only 2.4% of the catechin dose ingested was unaccounted for in the total volume of plasma, and in the day's urine and feces. It was assumed that the remainder was degraded in the intestine. Additionally, the relative proportions of the 4 catechins in the biological samples differed from their proportions in the tea. This information will be of value to scientists who study absorption and metabolism of catechins and other flavonoids.
Technical Abstract: Epidemiological studies have produced conflicting conclusions about the association between flavonoid intake and the reduced risk of both cancer and cardiovascular disease. Thus, studies of the bioavailability and metabolism of flavonoids are required to establish a link between tea consumption and improved health. This study investigated the absorptive and excretory processes associated with the intake of epigallocatechin, EGC; epicatechin, EC; epigallocatechin gallate, EGCG and epicatechin gallate, ECG in black tea. After 5 days on a low flavonoid diet, subjects drank a black tea preparation containing 15.48, 36.54, 16.74, and 31.14 mg of EGC, EGCG, EC and ECG, respectively at four time points (0, 2, 4 and 6 h.). Blood, urine and fecal specimens were collected over a 24-72 hour period and catechins were quantified by HPLC with coularray detection. Peak plasma EGC, EC, and EGCG concentrations were significantly different from baseline (p<0.05). Peak urinary concentrations of EGC and EC were significantly different from baseline (p<0.05). Concentrations of EGC, EC, EGCG, and ECG in fecal samples during tea consumption increased significantly over concentrations in baseline fecal samples (p<0.05). Catechins are bioavailable and the bioavailability of the gallated forms appears to differ from that of the non-gallated forms. Furthermore, the finding of only 2.4% of ingested catechins in the plasma urine, and feces is suggestive of considerable catechin metabolism or degradation either in the GI tract or after absorption.