Acute effects of ingestion of black and green tea on lipoprotein oxidation

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Abstract
Background: Tea has been associated with a reduced risk of cardiovascular disease. One proposed mechanism of this risk reduction involves inhibition of lipoprotein oxidation in vivo by antioxidant polyphenolic compounds derived from tea. However, controlled interventions uniformly failed to show that ingestion of tea can inhibit LDL oxidation ex vivo. The absence of effects in previous studies may be due to the isolation of LDL particles from polyphenolic compounds that are present in the aqueous phase of serum. Objective: The objective of this study was to examine the acute effects of ingestion of black and green tea on ex vivo Cu2+-induced lipoprotein oxidation without prior isolation of lipoproteins from serum. Design: The acute effects of 4 hot drinks—green tea and black tea (each at a dose equivalent to 4 standard cups), water matched to the teas for caffeine content, and water—were assessed in 20 healthy men by using a Latin-square design. The lag time to lipoprotein diene formation, slope of the propagation phase of the oxidation curve, and area under the oxidation curve were calculated. Urinary concentrations of 4-O-methylgallic acid were used as a marker of uptake and metabolism of polyphenolic compounds from tea. Results: Significant increases in urinary 4-O-methylgallic acid for black and green tea (P < 0.0001) were observed. Caffeine did not significantly influence lipoprotein oxidation. Compared with the water control, there was a greater lag time for black tea (5.4 ± 2.9 min; P = 0.05) that was of borderline significance and a similar trend for green tea (4.4 ± 2.8 min; P = 0.17). Slope and area under the oxidation curve were not altered. Conclusion: Black tea has a mild acute effect on ex vivo lipoprotein oxidation in human serum.