The effect of green tea on blood pressure in patients with type 2 diabetes mellitus: A systematic review and meta-analysis

Background and objectives: Previous trials conducted on patients with type 2 diabetes mellitus (T2DM) showed controversial results regarding the efficacy of green tea (GT) in improving blood pressure (BP). We conducted a review and meta-analysis of randomized controlled trials (RCTs) to summarize the effect of GT supplementation on BP among patients with T2DM. Methods and study design: Online databases, including PubMed/Medline, Scopus, and ISI web of science, were searched up to March 2021 to retrieve RCTs that examined the effect of GT on BP in patients with T2DM. Meta-analyses were carried out using a random effects model. The I2 index was used to evaluate the heterogeneity. Results: Among the initial 854 studies identified from electronic databases search, ten trials, which included 681 participants, were eligible. Pooled effect size from 10 studies indicated that supplementary intake of GT had no significant effect on systolic blood pressure (SBP) (Mean Difference (MD): 0.00 mmHg, 95 % CI: (-0.01, 0.01), p = 0.997), with no significant heterogeneity between the studies (I2 = 8.8 %, p = 0.356) and diastolic blood pressure (DBP) (MD:-0.90 mmHg, 95 % CI: (-2.21, 0.41), p = 0.178), with significant heterogeneity among the studies (I2 = 55.6 %, p = 0.006). Subgroup analysis revealed that GT supplementation lowers DBP when intervention is conducted on patients with elevated DBP. Conclusion: Our meta-analysis revealed that although GT supplementation has no significant effect on general BP in patients with T2DM, it may significantly improve DBP in patients with T2DM who have high DBP.