Tea consumption enhances endothelial-dependent vasodilation; a meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of placebo-controlled intervention trials
PubMed 21394199 · doi:10.1371/journal.pone.0016974
What was done
Authors conducted a systematic review and random-effects meta-analysis of human intervention studies searched across Medline, Embase, Chemical Abstracts, and Biosis through March 2009. Included studies used a placebo-controlled design with tea as the sole experimental variable and reported complete flow-mediated dilation (FMD) outcome and variability data.
What was found
Across 9 included studies with 15 study arms, a median daily dose of 500 mL of tea (2-3 cups) produced an overall absolute increase in brachial artery FMD of 2.6% (95% CI: 1.8% to 3.3%; P < 0.001) compared with placebo. This represented an approximate 40% relative increase over the mean baseline/placebo FMD of 6.3%. Significant between-study heterogeneity was observed (P < 0.001), partly explained by cuff placement (proximal vs. distal). No evidence of publication bias was found.
Why it matters
This meta-analysis provides evidence that moderate tea intake improves endothelial-dependent vasodilation in humans. This offers a plausible vascular mechanism for the lower cardiovascular disease and stroke risks seen in tea drinkers.
Limits
The abstract does not state the total number of participants, trial durations, or participant demographics. Significant statistical heterogeneity was present across the included studies. In addition, FMD is a surrogate vascular marker rather than a hard clinical endpoint, and the abstract does not report separate analyses for different tea types.
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