Effect of black tea intake on blood cholesterol concentrations in individuals with mild hypercholesterolemia: a diet-controlled randomized trial

Effects of Polyphenol-Rich Foods on Lipids and Oxidative Stress Status in Patients with Hyperlipidemia: A Systematic Review of Randomized Controlled Trials

Background

Hyperlipidemia has been demonstrated to be an autonomous predictor of numerous cardiovascular and cerebrovascular ailments, and research indicates that polyphenols have preventive and therapeutic effects on hyperlipidemia. Nevertheless, the impact of polyphenol-rich foods on blood lipids and oxidative stress status in patients with hyperlipidemia remains inconclusive.

Objective

To examine the impact of polyphenol-rich foods on lipid levels and oxidative stress in individuals with hyperlipidemia.

Methods

To retrieve papers published from the establishment of the database through October 9, 2023, eight databases were searched: the Chinese National Knowledge Infrastructure, the China Biomedical Literature Database, the Wanfang Database, the China Science and Technology Journal Database, PubMed, the Cochrane Library, Embase, and the Web of Science. The quality of include studies was assessed using the Cochrane Risk of Bias in Randomized Trials tool, v2.

Results

The study involved 13 surveys encompassing 640 patients diagnosed with hyperlipidemia. The scope of the food surveys included 12 commonly consumed food groups and medicinal and food homologous substances. All 13 studies reported the effects of polyphenol-rich foods on blood lipids, with significant improvements observed in blood lipid levels for 9 types of foods. Eight studies examined the impact on oxidative stress, and six foods demonstrated a significant reduction in oxidative stress levels. The observed effects were found to be influenced by factors such as dosage, duration of intervention, and gender.

Conclusion

Foods abundant in polyphenols play a crucial role in the prevention and treatment of hyperlipidemia by counteracting oxidative stress and regulating metabolic disorders. The confirmation of certain positive effects by several studies notwithstanding, discrepancies in results arise from various factors, necessitating further large-scale, prospective, well-designed randomized controlled studies to address this issue.

Tea's anti-obesity properties, cardiometabolic health-promoting potentials, bioactive compounds, and adverse effects: A review focusing on white and green teas

Tea is one of the most commonly consumed beverages in the world. Morocco, Japan, and China have consumed green tea for centuries. White tea, which is a variety of green teas, is very popular in China and is highly revered for its taste. Presently, both teas are consumed in other countries around the world, even as functional ingredients, and novel research is constantly being conducted in these areas. We provide an update on the health benefits of white and green teas in this review, based on recent research done to present. After a general introduction, we focused on tea's anti-obesity and human health-promoting potential, adverse effects, and new approaches to tea and its bioactive compounds. It has been found that the health benefits of tea are due to its bioactive components, mainly phenolic compounds. Of these, catechins are the most abundant. This beverage (or its extracts) has potential anti-inflammatory and antioxidant properties, which could contribute to body weight control and the improvement of several chronic diseases. However, some studies have mentioned the possibility of toxic effects; therefore, reducing tea consumption is a good idea, especially during the last trimester of pregnancy. Additionally, new evidence will provide insight into the possible effects of tea on the human gut microbiota, and even on the viruses responsible for SARS-CoV-2. A beverage such as this may favor beneficial gut microbes, which may have important implications due to the influence of gut microbiota on human health.

Efficacy of Dietary Polyphenols from Whole Foods and Purified Food Polyphenol Extracts in Optimizing Cardiometabolic Health: A Meta-Analysis of Randomized Controlled Trials

The evidence from clinical trials concerning the efficacy of dietary polyphenols on cardiometabolic health is divergent. Therefore, this review aimed to determine the pooled effect of dietary polyphenols on cardiometabolic risk markers and compare the difference in efficacy between whole polyphenol-rich foods and purified food polyphenol extracts. We conducted a random-effect model meta-analysis of randomized controlled trials (RCTs) on the effect of polyphenols on blood pressure, lipid profile, flow-mediated dilation (FMD), fasting blood glucose (FBG), waist circumference, and markers of inflammation. Effect size was expressed as weighted mean difference and 95% CI. RCTs published in English between 2000 and 2021 involving adult participants with cardiometabolic risks were searched in electronic databases. Forty-six RCTs involving 2494 participants with a mean age of 53.3 ±10 y were included in this review. Whole polyphenol-rich food but not purified food polyphenol extracts significantly reduced systolic blood pressure (SBP, -3.69 mmHg; 95% CI: -4.24, -3.15 mmHg; P = 0.00001) and diastolic blood pressure (DBP, -1.44 mmHg; 95% CI: -2.56, -0.31 mmHg; P = 0.0002). Concerning waist circumference, purified food polyphenol extracts led to a larger effect (-3.04 cm; 95% CI: -7.06, -0.98 cm; P = 0.14). Significant effects on total cholesterol (-9.03 mg/dL; 95% CI: -16.46, -1.06 mg/dL; P = 0.02) and TGs (-13.43 mg/dL; 95% CI: -23.63, -3.23; P = 0.01) were observed when purified food polyphenol extracts were considered separately. None of the intervention materials significantly affected LDL-cholesterol, HDL-cholesterol, FBG, IL-6, and CRP. When both whole food and extracts were pooled together, there was a significant reduction in SBP, DBP, FMD, TGs, and total cholesterol. These findings suggest that polyphenols both as whole food and purified extracts can be efficacious in reducing cardiometabolic risks. However, these results must be interpreted with caution because of high heterogeneity and risk of bias among RCTs. This study was registered on PROSPERO as CRD42021241807.

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

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.

Effects of tea consumption on metabolic syndrome: A systematic review and meta-analysis of randomized clinical trials

The metabolic syndrome (MetS) is one of the major health hazards and an epidemic worldwide. There is no known best remedy has been defined yet. In the current investigation, we designed a meta-analysis of randomized clinical trials (RCTs) to evaluate the beneficial effects of tea consumption in alleviating metabolic syndromes. Herein, we accumulated the relevant literature available on PubMed and EMBASE databases from January, 2000 to August, 2019. RCTs bearing impact factor of at least 1 or more were studied for the effect of tea consumption on MetS. This meta-analysis suggested that tea consumption has beneficial effects on diastolic blood pressure (DBP), and this finding was characterized of all types of tea in the current study and also for body mass index (BMI) value. Furthermore, this analysis also found that black tea consumption has protective effects on systolic SBP, green tea reduces the incidence of diabetes and lower the level of low-density lipoprotein (LDL) cholesterol. These functions required BMI value at least 28 or higher. The meta data led us to conclude that tea consumption have protective effects on MetS, however, different types of tea might have different protective mechanisms on MetS, but, exact mechanisms are not yet clear and needs to be explored.

Black tea and curcumin synergistically mitigate the hepatotoxicity and nephropathic changes induced by chronic exposure to aflatoxin-B1 in Sprague-Dawley rats

The study aimed to clarify the characteristics of black tea (BTE) and/or curcumin (CMN) against aflatoxin-B1 (AFB1). Forty eight adult male Sprague-Dawley rats were divided into eight groups. G1 was non-treated control. G2, G3, and G4 were olive oil, BTE, and CMN, respectively. G5 was olive oil-dissolved AFB1 (25 µg/kg b.w). G6, G7, and G8 were AFB1 along with BTE (2%), CMN (200 mg/kg b.w.), and BTE plus CMN, respectively. All treatments were orally given for consecutive 90 days. After treatment period, rats were sacrificed. Serobiochemical analysis and histopathology showed hepatorenal dysfunction in response to AFB1. Glutathione-antioxidants were significantly decreased versus increased lipid peroxides (p < .05-.001). AFB1 significantly increased the expression of the antitumor p53, but decreased that of antiapoptotic Bcl2 in liver or kidney tissue, either (p < .05). BTE or CMN ameliorated those changes induced by AFB1 in both liver and kidney with highly pronounced improvement when combined BTE/CMN was used. PRACTICAL APPLICATIONS: Black tea (BTE) and curcumin (CMN) were known for their antioxidant effects, and several studies reported their independent effects against different toxicities including aflatoxicosis. The current study clarifies the ameliorative characteristics of both agents; BTE and/or CMN, against the toxicity resulted from the chronic exposure to aflatoxin-B1 (AFB1) (25 µg/kg b.w. for consecutive 90 days). The dose of either agents, BTE or CMN, was 200 mg/kg b.w. along with AFB1. The pathologic changes, serobiochemical parameters, oxidative stress, histological changes, and the molecular disruption, induced by AFB1 in both liver and kidney were obviously and significantly ameliorated after BTE and/or CMN treatments in variable potencies where both agents showed the most effective antitoxic capacities.

The Pharmacological Activity of Camellia sinensis (‎L.‎) ‎Kuntze‎ on Metabolic and Endocrine Disorders: A Systematic Review

Tea made from Camellia sinensis leaves is one of the most consumed beverages worldwide. This systematic review aims to update Camellia sinensis pharmacological activity on metabolic and endocrine disorders. Inclusion criteria were preclinical and clinical studies of tea extracts and isolated compounds on osteoporosis, hypertension, diabetes, metabolic syndrome, hypercholesterolemia, and obesity written in English between 2014 and 2019 and published in Pubmed, Science Direct, and Scopus. From a total of 1384 studies, 80 reports met inclusion criteria. Most papers were published in 2015 (29.3%) and 2017 (20.6%), conducted in China (28.75%), US (12.5%), and South Korea (10%) and carried out with extracts (67.5%, especially green tea) and isolated compounds (41.25%, especially epigallocatechin gallate). Most pharmacological studies were in vitro and in vivo studies focused on diabetes and obesity. Clinical trials, although they have demonstrated promising results, are very limited. Future research should be aimed at providing more clinical evidence on less studied pathologies such as osteoporosis, hypertension, and metabolic syndrome. Given the close relationship among all endocrine disorders, it would be of interest to find a standard dose of tea or their bioactive constituents that would be beneficial for all of them.

Temporal Requirement for the Protective Effect of Dietary Cholesterol against Alcohol-Induced Vasoconstriction

Moderate-to-heavy episodic alcohol drinking resulting in 30-80 mM of ethanol in blood constricts cerebral arteries and constitutes a risk factor for cerebrovascular disease. Alcohol-induced constriction of cerebral arteries in vivo and ex vivo has been shown to be blunted by dietary cholesterol (CLR) in a rat model of a high-CLR diet. Such protection has been proposed to arise from the high-CLR diet-driven increase in blood CLR levels and accompanying buildup of CLR within the cerebral artery smooth muscle. Here we used a rat model of high-CLR feeding in vivo and pressurized cerebral arteries ex vivo to examine whether the degree and time-course of alcohol-induced constriction are related to blood CLR levels. We demonstrate that subjecting young (3 weeks-old, 50 g) male Sprague-Dawley rats to a high- CLR feeding up to 41 weeks, resulted in an age-dependent increase in total blood CLR levels, when compared to those of age-matched rats on isocaloric (control) chow. This increase was paralleled by a high-CLR diet-driven elevation of blood low-density lipoproteins whereas high-density lipoprotein levels matched those of age-matched, chow-fed controls. Alcohol-induced constriction was only blunted by high-CLR dietary intake when high-CLR chow was taken for up to 8-12 and 18-23 weeks. However, alcohol-constriciton was not blunted when high-CLR chow intake lasted for longer times, such as 28-32 and 38-41 weeks. Thus, alcohol-induced constriction of rat middle cerebral arteries did not critically depend on the total blood CLR levels. Alcohol-induced constriction seemed unrelated to the natural, progressive elevation of the total blood CLR level in control- or high-CLR-fed animals over time. Thus, neither the exogenously nor endogenously driven increases in blood CLR could predict cerebral artery susceptibility to alcohol-induced constriction. However, we identified a temporal requirement for the protective effect of dietary CLR against alcohol, that could be governed by the young age of the high- CLR chow recipients (3 weeks of age) and/or the short duration of high-CLR chow feeding lasting for up to 23 weeks.

Health Functions and Related Molecular Mechanisms of Tea Components: An Update Review

Tea is widely consumed all over the world. Generally, tea is divided into six categories: White, green, yellow, oolong, black, and dark teas, based on the fermentation degree. Tea contains abundant phytochemicals, such as polyphenols, pigments, polysaccharides, alkaloids, free amino acids, and saponins. However, the bioavailability of tea phytochemicals is relatively low. Thus, some novel technologies like nanotechnology have been developed to improve the bioavailability of tea bioactive components and consequently enhance the bioactivity. So far, many studies have demonstrated that tea shows various health functions, such as antioxidant, anti-inflammatory, immuno-regulatory, anticancer, cardiovascular-protective, anti-diabetic, anti-obesity, and hepato-protective effects. Moreover, it is also considered that drinking tea is safe to humans, since reports about the severe adverse effects of tea consumption are rare. In order to provide a better understanding of tea and its health potential, this review summarizes and discusses recent literature on the bioactive components, bioavailability, health functions, and safety issues of tea, with special attention paid to the related molecular mechanisms of tea health functions.

Effectiveness of black tea versus placebo in subjects with hypercholesterolemia: A PRISMA systematic review and meta-analysis

AIM

To determine if the black tea is more effective in serum lipid profile that placebo in subjects with hypercholesterolemia.

DESIGN

Systematic review with meta-analysis of randomized clinical trials (RCTs).

DATA SOURCES

The databases Medline, Central, Embase, Lilacs, Cinahl, SPORTDiscus, and Web of Science were searched from inception up to January 2019.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

RCTs that compared black tea versus placebo, that included serum lipid profile outcomes in subjects older than 18 years of age with hypercholesterolemia.

RESULTS

Seven RCTs met the eligibility criteria, and for the quantitative synthesis, six studies were included. Mean difference for total cholesterol was 1.67 mg/dl 95% CI = -5.47 to 8.80 (p = 0.65), mean difference 0.28 mg/dl, 95% CI = -3.89 to 4.45 (p = 0.90) for triglycerides, mean difference 3.21 mg/dl, 95% CI = -11.02 to 4.60 (p = 0.42) for low density lipoprotein-cholesterol, mean difference 0.38 mg/dl, 95% CI = -1.12 to 1.87 (p = 0.62) for high density lipoprotein-cholesterol.

CONCLUSION

In the short term, no significant differences were found in lipid serum profile comparing black tea consumption with placebo.

Comparative effect of black, green, oolong, and white tea intake on weight gain and bile acid metabolism

OBJECTIVE

The beneficial effects of tea on health, including obesity, are well known. However, the comparative effects of black, green, white, and oolong teas, which are prepared from the same fresh leaves, on weight gain and the potential mechanisms involved are not yet fully understood. Bile acids (BAs) are shown to be powerful regulators of metabolism; however, to our knowledge, no studies have investigated the effect of tea on BA metabolism. The aim of this study was to investigate the modulatory effects that green, black, white, and oolong teas that were prepared from the same raw tea leaves have on the plasma BA profile.

METHODS

Female rats were dosed with the aforementioned tea types as their sole source of drinking fluid for 28 d. We then investigated their weight and effect on BA metabolic profile using advanced ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS)-based metabolomics.

RESULTS

The UPLC-MS/MS analysis of the plasma show that the levels of murocholic acid, glycochenodeoxycholic acid, glycocholic acid, glycodeoxycholic acid, taurochenodeoxycholic acid, tauroursodeoxycholic acid, taurodeoxycholic acid, tauromuricholic acid, and taurocholic acid were increased; whereas levels of taurolithocholic acid and isolithocholic acid were decreased after drinking green, oolong, and white tea types compared with control. Surprisingly, oolong tea significantly influenced reduction in relative weight compared with control, black, and green tea; whereas black, green, and white teas had no effects on weight compared with control.

CONCLUSIONS

Green, black, oolong, and white teas altered the BA metabolism. This change in BA metabolism could be associated with the health benefit effects of tea. Oolong tea was most effective in reducing weight.

Tea Consumption and Longitudinal Change in High-Density Lipoprotein Cholesterol Concentration in Chinese Adults

Background

The relation between tea consumption and age‐related changes in high‐density lipoprotein cholesterol (HDL‐C) concentrations remains unclear, and longitudinal human data are limited. The aim of current study was to examine the relation between tea intake and longitudinal change in HDL‐C concentrations.

Methods and Results

Baseline (2006) tea consumption was assessed via a questionnaire, and plasma HDL‐C concentrations were measured in 2006, 2008, 2010, and 2012 among 80 182 individuals (49±12 years of age) who did not have cardiovascular diseases or cancer, or did not use cholesterol‐lowering agents both at baseline (2006) and during the follow‐up period (2006–2012). The associations between baseline tea consumption and rate of change in HDL‐C concentrations were examined using generalized estimating equation models. Tea consumption was inversely associated with a decreased rate of HDL‐C concentrations (P‐trend <0.0001) in the fully adjusted model. The adjusted mean difference in the HDL‐C decreased rate was 0.010 (95% confidence interval, 0.008, 0.012) mmol/L per year for tea consumers versus nonconsumers (never or less than once/month group). Interactions between tea consumption and age, sex, lifestyle scores, and metabolic syndrome (all P‐interaction <0.0001) were identified. The associations between greater tea consumption and slower decrease in HDL‐C concentrations were more pronounced in men, individuals aged 60 or older, individuals with a lower lifestyle score, and individuals with metabolic syndrome (all P‐trend <0.0001).

Conclusions

Tea consumption was associated with slower age‐related decreases in HDL‐C concentrations during 6 years of follow‐up.

Clinical Trial Registration

URL: http://www.chictr.org. Unique identifier: ChiCTR‐TNRC‐11001489.

Pharmacological values and therapeutic properties of black tea (Camellia sinensis): A comprehensive overview

Medicinal plants are essential parts of traditional medicine due to their phytochemical constituents having pharmacological values and therapeutic applications. Black tea have thousands of various biological compounds such as flavonoids (Thearubigins (TRs) and theaflavins (TFs) and catechins), amino acids (L.theanine), vitamins (A, C, K), phenolic acids (caffeic acid (CA), gallic acid (GA), chlorogenic acids (CGA) and cauramic acid), lipids, proteins, volatile compounds carbohydrates, β-carotene and fluoride that illustrated many promising pharmacological effects regarded as growth promoter, cardioprotector, potent cholesterol-lowering effect, antioxidant and antimicrobial, etc inhuman. Although there is an exponential growth in molecular evidence of cholesterol-lowering and antioxidant effect in human, there is still a lack of information of the pharmacological effects of black tea. To fill this information gap, therefore, this review article underscores broadening the new insight pertaining to black tea that could be used as safe food additive. This article also illuminates the interesting role of black tea as an herbal medicine that is the future demand to get rid of synthetic health promoters in the human health practice. Moreover, this information would be useful in terms of the low-cost practice of natural medicines with no residual effects, and a natural protection of the human being. In addition, further studies at a molecular level are needed to reveal its mechanism of action particularly for the hypocholesterolemic effect of black tea to overcome the heart-related diseases, fewer side effects and being a natural safeguard of human health.

A Systematic Review and Meta-Analysis of the Effects of Flavanol-Containing Tea, Cocoa and Apple Products on Body Composition and Blood Lipids: Exploring the Factors Responsible for Variability in Their Efficacy

Several randomized controlled trials (RCTs) and meta-analyses support the benefits of flavanols on cardiometabolic health, but the factors affecting variability in the responses to these compounds have not been properly assessed. The objectives of this meta-analysis were to systematically collect the RCTs-based-evidence of the effects of flavanol-containing tea, cocoa and apple products on selected biomarkers of cardiometabolic risk and to explore the influence of various factors on the variability in the responses to the consumption of these products. A total of 120 RCTs were selected. Despite a high heterogeneity, the intake of the flavanol-containing products was associated using a random model with changes (reported as standardized difference in means (SDM)) in body mass index (−0.15, p < 0.001), waist circumference (−0.29, p < 0.001), total-cholesterol (−0.21, p < 0.001), LDL-cholesterol (−0.23, p < 0.001), and triacylglycerides (−0.11, p = 0.027), and with an increase of HDL-cholesterol (0.15, p = 0.005). Through subgroup analyses, we showed the influence of baseline-BMI, sex, source/form of administration, medication and country of investigation on some of the outcome measures and suggest that flavanols may be more effective in specific subgroups such as those with a BMI ≥ 25.0 kg/m², non-medicated individuals or by specifically using tea products. This meta-analysis provides the first robust evidence of the effects induced by the consumption of flavanol-containing tea, cocoa and apple products on weight and lipid biomarkers and shows the influence of various factors that can affect their bioefficacy in humans. Of note, some of these effects are quantitatively comparable to those produced by drugs, life-style changes or other natural products. Further, RCTs in well-characterized populations are required to fully comprehend the factors affecting inter-individual responses to flavanol and thereby improve flavanols efficacy in the prevention of cardiometabolic disorders.

Black tea polyphenols and polysaccharides improve body composition, increase fecal fatty acid, and regulate fat metabolism in high-fat diet-induced obese rats

With the current changes in diet and living habits, obesity has become a global health problem. Thus, the weight-reducing function of tea has attracted considerable attention. This study investigated the anti-obesity effect and the mechanism of black tea (BT) polyphenols and polysaccharides in male Sprague-Dawley rats. The BT polyphenols and polysaccharides reduced the body weight, Lee's index, visceral fat weight, and fat cell size but improved the biochemical profile and increased the fecal fatty acid content, thereby preventing high-fat diet-induced obesity. A gene expression profile array was used to screen eight upregulated and five downregulated differentially expressed genes that affect fat metabolic pathways, such as glycerolipid and glycerophospholipid metabolism, fatty acid degradation, glycolysis and gluconeogenesis, bile and pancreatic secretion, the insulin signaling pathway, and steroid hormone secretion. The BT polyphenols and polysaccharides suppressed the formation and accumulation of fat and promoted its decomposition to prevent obesity.