Association between tea consumption and prevention of coronary artery disease: A systematic review and dose-response meta-analysis

Evaluating the effect of green tea intake on cardiovascular diseases: A Mendelian randomization study in European and East Asian populations

Previous research shows that more than 70% of cardiovascular diseases (CVDs) are attributed to modifiable risk factors. Here, we investigated relationship between consumption of green tea in European and East Asian populations and risk of CVDs using Mendelian randomization (MR). Instrumental variables for green tea intake were obtained from genome-wide association studies (GWASs) of 64,949 Europeans and 152,653 East Asians. GWASs for CVDs were derived from UK BioBank and BioBank Japan projects. The main method selected for MR analysis was either the inverse variance weighted (IVW) or Wald ratio, depending on the quantity of single nucleotide polymorphisms. Furthermore, we performed sensitivity analyses to confirm the reliability of the findings. Based on the results of IVW, there is no causal relationship between consumption of green tea and risk of 4 CVDs among Europeans (atrial fibrillation: OR = 1.000, 95% CI: 0.995-1.005, P = .910; heart failure: OR = 1.003, 95% CI: 0.994-1.012, P = .542; ischemic stroke: OR = 1.002, 95% CI: 0.993-1.011, P = .690; coronary artery disease: OR = 1.001, 95% CI: 0.996-1.007, P = .677). Sensitivity analyses and supplementary MR analyses also verify the robustness of the findings. Likewise, there was no correlation between the consumption of green tea and the occurrence of CVDs in East Asians. The consumption of green tea is not associated with a reduced risk of CVDs in populations from Europe and East Asia. This means that those who are trying to reduce their risk of CVDs by drinking more green tea may not benefit from doing so.

Anji white tea relaxes precontracted arteries, represses voltage-gated Ca2+ channels and voltage-gated K+ channels in the arterial smooth muscle cells: Comparison with green tea main component (-)-epigallocatechin gallate

ETHNOPHARMACOLOGICAL RELEVANCE

Tea (Camellia sinensis) is a favorite drink worldwide. Tea extracts and green tea main component (-)-epigallocatechin gallate (EGCG) are recommended for various vascular diseases. Anji white tea is a very popular green tea. Its vascular effect profile, the mechanisms, and the contribution of EGCG to its integrated effect need elucidation.

AIM

To characterize the vasomotion effects of Anji white tea and EGCG, and to explore possible involvement of voltage-gated Ca2+ channels (VGCCs) and voltage-gated K+ (Kv) channels in their vasomotion effects.

MATERIALS AND METHODS

Anji white tea water soaking solution (AJWT) was prepared as daily tea-making process and concentrated to a concentration amounting to 200 mg/ml of dry tea leaves. The tension of rat arteries including aorta, coronary artery (RCA), cerebral basilar artery (CBA), intrarenal artery (IRA), intrapulmonary artery (IPA) and mesenteric artery (MA) was recorded with myographs. In arterial smooth muscle cells (ASMCs) freshly isolated from RCA, the levels of intracellular Ca2+ were measured with Ca2+-sensitive fluorescent probe fluo 4-AM, and Kv currents were recorded with patch clamp. The expressions of VGCCs and Kv channels were assayed with RT-qPCR and immunofluorescence staining.

RESULTS

At 0.4-12.8 mg/ml of dry tea leaves, AJWT profoundly relaxed all tested arteries precontracted with various vasoconstrictors about half with a small transient potentiation on the precontractions before the relaxation. KCl-induced precontraction was less sensitive than precontractions induced by phenylephrine (PE), U46619 and serotonin (5-HT). IPA was less sensitive to the relaxation compared with other arteries. AJWT pretreatment for 1 h, 24 h and 72 h time-dependently inhibited the contractile responses of RCAs. In sharp contrast, at equivalent concentrations according to its content in AJWT, EGCG intensified the precontractions in most small arteries, except that it induced relaxation in PE-precontracted aorta and MA, U46619-precontracted aorta and CBA. EGCG pretreatment for 1 h and 24 h did not significantly affect RCA contractile responses. In RCA ASMCs, AJWT reduced, while EGCG enhanced, intracellular Ca2+ elevation induced by depolarization which activates VGCCs. Patch clamp study showed that both AJWT and EGCG reduced Kv currents. RT-qPCR and immunofluorescence staining demonstrated that both AJWT and EGCG reduced the expressions of VGCCs and Kv channels.

CONCLUSION

AJWT, but not EGCG, consistently induces vasorelaxation. The vasomotion effects of either AJWT or EGCG vary with arterial beds and vasoconstrictors. Modulation of VGCCs, but not Kv channels, contributes to AJWT-induced vasorelaxation. It is suggested that Anji white tea water extract instead of EGCG may be a promising food supplement for vasospastic diseases.

A green tea extract confection decreases circulating endotoxin and fasting glucose by improving gut barrier function but without affecting systemic inflammation: A double-blind, placebo-controlled randomized trial in healthy adults and adults with metabolic syndrome

Anti-inflammatory activities of catechin-rich green tea extract (GTE) in obese rodents protect against metabolic endotoxemia by decreasing intestinal permeability and absorption of gut-derived endotoxin. However, translation to human health has not been established. We hypothesized that GTE would reduce endotoxemia by decreasing gut permeability and intestinal and systemic inflammation in persons with metabolic syndrome (MetS) compared with healthy persons. A randomized, double-blind, placebo-controlled, crossover trial in healthy adults (n = 19, 34 ± 2 years) and adults with MetS (n = 21, 40 ± 3 years) examined 4-week administration of a decaffeinated GTE confection (890 mg/d total catechins) on serum endotoxin, intestinal permeability, gut and systemic inflammation, and cardiometabolic parameters. Compared with the placebo, the GTE confection decreased serum endotoxin (P = .023) in both healthy persons and those with MetS, while increasing concentrations of circulating catechins (P < .0001) and γ-valerolactones (P = .0001). Fecal calprotectin (P = .029) and myeloperoxidase (P = .048) concentrations were decreased by GTE regardless of health status. Following the ingestion of gut permeability probes, urinary lactose/mannitol (P = .043) but not sucralose/erythritol (P > .05) was decreased by GTE regardless of health status. No between-treatment differences (P > .05) were observed for plasma aminotransferases, blood pressure, plasma lipids, or body mass nor were plasma tumor necrosis factor-α, interleukin-6, or the ratio of lipopolysaccharide-binding protein/soluble cluster of differentiation-14 affected. However, fasting glucose in both study groups was decreased (P = .029) by the GTE confection compared with within-treatment arm baseline concentrations. These findings demonstrate that catechin-rich GTE is effective to decrease circulating endotoxin and improve glycemic control in healthy adults and those with MetS, likely by reducing gut inflammation and small intestinal permeability but without affecting systemic inflammation.

The Antiobesity Effects and Potential Mechanisms of Theaflavins

Theaflavins are the characteristic polyphenols in black tea which can be enzymatically synthesized. In this review, the effects and molecular mechanisms of theaflavins on obesity and its comorbidities, including dyslipidemia, insulin resistance, hepatic steatosis, and atherosclerosis, were summarized. Theaflavins ameliorate obesity potentially via reducing food intake, inhibiting pancreatic lipase to reduce lipid absorption, activating the adenosine monophosphate-activated protein kinase (AMPK), and regulating the gut microbiota. As to the comorbidities, theaflavins ameliorate hypercholesterolemia by inhibiting micelle formation to reduce cholesterol absorption. Theaflavins improve insulin sensitivity by increasing the signaling of protein kinase B, eliminating glucose toxicity, and inhibiting inflammation. Theaflavins ameliorate hepatic steatosis via activating AMPK. Theaflavins reduce atherosclerosis by upregulating nuclear factor erythropoietin-2-related factor 2 signaling and inhibiting plasminogen activator inhibitor 1. In randomized controlled trails, black tea extracts containing theaflavins reduced body weight in overweight people and improved glucose tolerance in healthy adults. The amelioration on the hyperlipidemia and the prevention of coronary artery disease by black tea extracts were supported by meta-analysis.

First ATR-FTIR Characterization of Black, Green and White Teas (Camellia sinensis) from European Tea Gardens: A PCA Analysis to Differentiate Leaves from the In-Cup Infusion

ATR-FTIR (Attenuated Total Reflectance Fourier Transform InfraRed) spectroscopy, combined with chemometric, represents a rapid and reliable approach to obtain information about the macromolecular composition of food and plant materials. With a single measurement, the chemical fingerprint of the analyzed sample is rapidly obtained. Hence, this technique was used for investigating 13 differently processed tea leaves (green, black and white) all grown and processed in European tea gardens, and their vacuum-dried tea brews, prepared using both hot and cold water, to observe how the components differ from tea leaf to the in-cup infusion. Spectra were collected in the 1800-600 cm-1 region and were submitted to Principal Component Analysis (PCA). The comparison of the spectral profiles of leaves and hot and cold infusions of tea from the same country, emphasizes how they differ in relation to the different spectral regions. Differences were also noted among the different countries. Furthermore, the changes observed (e.g., at ~1340 cm-1) due to catechin content, confirm the antioxidant properties of these teas. Overall, this experimental approach could be relevant for rapid analysis of various tea types and could pave the way for the industrial discrimination of teas and of their health properties without the need of time-consuming, lab chemical assays.

Long-Term Consumption of Green Tea Can Reduce the Degree of Depression in Postmenopausal Women by Increasing Estradiol

Postmenopausal women face a higher risk of depression due to a combination of social and physiological factors. As a beverage rich in a variety of bioactive substances, green tea has significant effects on metabolism, inflammation and endocrine, and may reduce the risk of depression, but few studies have looked at the effects of green tea on postmenopausal women. Therefore, we designed this study to investigate the effects of long-term green tea consumption on inflammation, endocrine and depression levels in postmenopausal women. We investigated a tea-producing village and eventually included 386 postmenopausal women, both in the tea drinking and control groups. The results showed that there were significant differences in the degree of insomnia, degree of depression, BMI, SII and estradiol between the two groups. And, green tea consumption may reduce the risk of depression through the mediating pathway of sleep, SII and estradiol. In summary, long-term green tea consumption can reduce the risk of depression in postmenopausal women by reducing inflammation and increasing estradiol. This kind of living habit deserves further promotion.