Does Green or Black Tea Help to Prevent CVD?

The main objective of this study was to determine the effects of green and black tea on the primary prevention of cardiovascular disease. A database search was used to find participants for the study. Trial registers, screened reference lists and personal contacts were also used for additional information when necessary.

To be included in the review participants had to be in a randomized controlled trial lasting at least three months involving healthy adults or those at high risk of cardiovascular disease. These trials investigated the intake of green tea, black tea or tea extracts and their effects on cardiovascular events. The comparison group was no intervention, placebo or minimal intervention. The outcomes of interest were cardiovascular events and major cardiovascular risk factors. Any trials involving multifactorial lifestyle interventions or focusing on weight loss were excluded to avoid confounding variables in the study.

The main results to the study came from 11 randomized controlled trials with a total of 821 participants. Seven trials examined a green tea intervention and four examined a black tea intervention. Dosage and form of both green and black tea differed between trials.

Results of the investigation showed that black tea was found to produce statistically significant reductions in low-density lipoprotein (LDL) cholesterol (mean difference (MD) -0.43 mmol/L and blood pressure (systolic blood pressure (SBP): MD -1.85 mmHg. It was also shown to decrease diastolic blood pressure approximately -1.27 mmHg over six months. It should be noted that only a small number of trials contributed to each analysis and studies were at risk of bias.

Green tea was also found to produce statistically significant reductions in total cholesterol (MD -0.62 mmol/L), LDL cholesterol (MD -0.64 mmol/L) and blood pressure (SBP: MD -3.18 mmHg) but only a small number of studies contributed to each analysis, and results were not stable to sensitivity analysis. When both tea types were analyzed together they showed beneficial effects on LDL cholesterol (MD -0.48 mmol/L) and blood pressure (SBP: MD -2.25 mmH; DBP: MD -2.81 mmHg). Adverse events were measured in five trials and included a diagnosis of prostate cancer, hospitalization for influenza, appendicitis and retinal detachment but these are unlikely to be directly attributable to the intervention.

Final conclusions from the author showed that there are very few long-term studies examining green or black tea for the primary prevention of cardiovascular disease. The limited evidence suggests that tea has beneficial effects on cardiovascular risk factors, but due to the small number of trials contributing to each analysis the results should be further investigated with high quality trials including a longer duration of follow-up time are needed to finalize the results.

Hartley , Luis . "Green and black tea for the primary prevention of cardiovascular disease." The Cochrane Collaboration, July 8, 2013.