Short-Term Tea Consumption Is Not Associated with a Reduction in Blood Lipids or Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Abstract

Background A recent systematic review of epidemiological evidence suggests that higher amounts of tea intake are associated with lower risks of cardiovascular disease (CVD) incidence and mortality. Objectives Our study objective was to assess mechanisms by which tea consumption may influence CVD risks. Methods A systematic review and meta-analysis was conducted to investigate the effects of green and/or black tea consumption (≥4 wk) on systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride (TG) in healthy populations and among at-risk adults (analyzed separately) with metabolic syndrome, prediabetes, and hypercholesterolemia. The Grading of Recommendations Assessment, Development and Evaluation approach was used to rate the strength of evidence (SoE). Results A total of 14 unique RCTs which randomly assigned 798 participants to either green tea, black tea, or placebo controls were included in our analyses. Intervention durations ranged from 4 to 24 wk (mean: 7.4 wk). Individual studies were judged as moderate to high quality based on risk of bias assessments. SoE was low to moderate owing to low sample sizes and insufficient power for most included studies to observe changes in the measured CVD biomarkers. Meta-analyses showed no significant effects of tea consumption on SBP, DBP, total cholesterol, LDL cholesterol, HDL cholesterol, and TG in healthy and at-risk adults (i.e., adults with obesity, prediabetes, borderline hypercholesterolemia, and metabolic syndrome). Conclusions Short-term (4–24 wk) tea consumption does not appear to significantly affect blood pressure or lipids in healthy or at-risk adults, although the evidence is limited by insufficient power to detect changes in these CVD biomarkers. High-quality RCTs with longer durations and sufficient sample sizes are needed to fully elucidate the effects of tea. This systematic review was registered at www.crd.york.ac.uk/prospero/ as CRD42020134513.

Polyphenol-Rich and Alcoholic Beverages and Metabolic Status in Adults Living in Sicily, Southern Italy

“…Regarding the null results on diabetes, we may hypothesize that doses of coffee might not be sufficient to reduce the risk as reported in the scientific literature, or unmeasured confounding factors (i.e., the use of sugar in coffee) might counteract its beneficial effects on insulin sensitivity and glucose homeostasis. Regarding tea, summary of evidence showed it does not appear to significantly affect blood pressure or lipids in short-term [49], while data on metabolic outcomes are mixed and seems to potentially depend on type of tea and doses (i.e., associations observed for higher intake than those reported in our study, which may explain lack of significant findings) [16,50].…”

Tea intake and cardiovascular disease: an umbrella review

“…Xu et al found a significant decrease in total cholesterol among normal weight, overweight, and obese individuals (combined) who consumed green tea vs. placebo (weighted mean difference [WMD]: −4.66 mg/dL; 95% CI: 6.36 to −2.96; p = .0001) in a random effects meta-analysis [ 31 ]. The remaining nine older systematic reviews found no significant effects on total cholesterol across various populations [ 3 , 11 , 18 , 19 , 22 , 27 , 30 , 34 , 49 ], which may be due to a smaller number of studies and overall sample size. The quality of these systematic reviews was judged to be low to high ( Table 2 ).…”

“…Twelve systematic reviews assessing effects of tea consumption on high-density lipoprotein (HDL) cholesterol were identified from our literature search [ 3 , 11 , 18 , 19 , 22 , 24 , 26 , 27 , 30 , 31 , 34 , 49 ]. Study populations ranged from healthy individuals and the general adult population to individuals with high CVD risk, hypercholesterolaemia, type-2 diabetes, prediabetes, obesity with metabolic syndrome, or hypertension.…”

“…One study included some adolescents [ 22 ]. These systematic reviews consistently failed to show significant effects on HDL cholesterol across various populations [ 3 , 11 , 18 , 19 , 22 , 24 , 26 , 27 , 30 , 31 , 34 , 49 ]. The quality of these systematic reviews was judged to be critically low to high ( Table 2 ).…”

“…Asbaghi et al (2020) found a significant decrease in triglycerides among individuals with type 2 diabetes who consumed green tea vs. placebo (WMD: −12.79 mg/dL; 95% CI: −24.74 to −0.84; p = .036) in a random effects meta-analysis [ 19 ]. The remaining 10 systematic reviews found no significant effects on triglycerides across various populations [ 3 , 11 , 18 , 22 , 24 , 26 , 27 , 30 , 31 , 49 ]. The quality of these systematic reviews was judged to be critically low to high ( Table 2 ).…”