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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: BACKGROUND, OBJECTIVES, DESIGN, RESULTS. Meshes: Adult, Aged, Blood Pressure, Body Mass Index, Cholesterol, Cross-Over Studies, Female, Flavonoids, Folic Acid, Gallic Acid, Homocysteine, Humans, Lipids, Male, Methylation, Middle Aged, Phenols, Polymers, Polyphenols, Tea, Vitamin B 12, Vitamin B 6.
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Can black tea influence plasma total homocysteine concentrations? Context: 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. 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. 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. Black tea did not significantly alter mean (+/- SEM) tHcy concentrations (9.9 +/- 0.5 and 10.0 +/- 0.5 micro mol/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 micro mol/L; P = 0.046), and those in the top quartile had a significant increase in tHcy (0.78 +/- 0.16 micro mol/L; P = 0.005).
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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.