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Can black tea influence plasma total homocysteine concentrations?^1,2,3

¹ From the School of Medicine & Pharmacology, University of Western Australia, and the Western Australian Institute for Medical Research, Royal Perth Hospital, Perth, Australia.

Background: Polyphenols can act as acceptors of methyl groups during the metabolism of methionine to homocysteine. This may result in elevations in plasma total homocysteine (tHcy) concentrations after ingestion of polyphenol-rich beverages such as tea.

Objectives: Our major objective was to determine whether regular, moderate-to-high intakes of black tea alter tHcy concentrations. We also assessed the relation between the degree of O-methylation of tea-derived polyphenols and the change in tHcy with regular ingestion of tea.

Design: Twenty-two subjects completed a randomized, controlled crossover study. Subjects consumed 1250 mL black tea/d (5 cups each containing 2 g tea leaves in 250 mL boiled water) and 1250 mL hot water/d for 4 wk each. Fasting tHcy concentrations and 24-h urinary excretion of 4-O-methylgallic acid (4OMGA, the major O-methylated metabolite of gallic acid) were measured at the end of each period. 4OMGA was used as a marker of overall O-methylation of tea-derived polyphenols.

Results: Black tea did not significantly alter mean (± SEM) tHcy concentrations (9.9 ± 0.5 and 10.0 ± 0.5 µmol/L for the hot water and black tea periods, respectively). However, the increased excretion of 4OMGA as a consequence of black tea consumption was positively associated with the change in tHcy from the hot water period to the black tea period (r = 0.55, P = 0.008). Subjects in the bottom quartile of increase in 4OMGA excretion had a significant decrease in tHcy (-0.28 ± 0.10 µmol/L; P = 0.046), and those in the top quartile had a significant increase in tHcy (0.78 ± 0.16 µmol/L; P = 0.005).

Conclusions: Overall, regular ingestion of black tea did not alter mean tHcy concentrations. However, individual differences in O-methylation of polyphenolic compounds may influence the ultimate effects of black tea on tHcy.

Key Words: Black tea • total homocysteine • polyphenols • O-methylation • urinary 4-O-methylgallic acid

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