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Green tea (Camellia sinensis) for the prevention of cancer.
Filippini, T, Malavolti, M, Borrelli, F, Izzo, AA, Fairweather-Tait, SJ, Horneber, M, Vinceti, M
The Cochrane database of systematic reviews. 2020;3(3):CD005004
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Brewed tea is obtained from the infusion of leaves and buds of Camellia sinensis. The most consumed types of tea are green and black tea. Due to the high content of antioxidant compounds, a great deal of attention has been given to green tea regarding the possible prevention of chronic diseases and cancer, as well as possible beneficial effects on cardiovascular disease, insulin sensitivity and lipid profiles. The main aim of this review was to assess the association between green tea consumption and the risk of developing cancer in epidemiologic studies. This study is an update of a previously published Cochrane review based on studies in which participants consumed green tea orally, either as drinkable tea or as extracts. One hundred and forty-two epidemiological studies of experimental and nonexperimental design were included with a total of 1,100,000 participants. Findings yielded inconsistent results for the effect of green tea consumption on cancer risk, despite some indications of a beneficial effect of green tea on a few site-specific cancers. Authors conclude that the epidemiological evidence appears to be still inadequate to support a beneficial effect of green tea on cancer risk.
Abstract
BACKGROUND This review is an update of a previously published review in the Cochrane Database of Systematic Reviews (2009, Issue 3).Tea is one of the most commonly consumed beverages worldwide. Teas from the plant Camellia sinensis can be grouped into green, black and oolong tea, and drinking habits vary cross-culturally. C sinensis contains polyphenols, one subgroup being catechins. Catechins are powerful antioxidants, and laboratory studies have suggested that these compounds may inhibit cancer cell proliferation. Some experimental and nonexperimental epidemiological studies have suggested that green tea may have cancer-preventative effects. OBJECTIVES To assess possible associations between green tea consumption and the risk of cancer incidence and mortality as primary outcomes, and safety data and quality of life as secondary outcomes. SEARCH METHODS We searched eligible studies up to January 2019 in CENTRAL, MEDLINE, Embase, ClinicalTrials.gov, and reference lists of previous reviews and included studies. SELECTION CRITERIA We included all epidemiological studies, experimental (i.e. randomised controlled trials (RCTs)) and nonexperimental (non-randomised studies, i.e. observational studies with both cohort and case-control design) that investigated the association of green tea consumption with cancer risk or quality of life, or both. DATA COLLECTION AND ANALYSIS Two or more review authors independently applied the study criteria, extracted data and assessed methodological quality of studies. We summarised the results according to diagnosis of cancer type. MAIN RESULTS In this review update, we included in total 142 completed studies (11 experimental and 131 nonexperimental) and two ongoing studies. This is an additional 10 experimental and 85 nonexperimental studies from those included in the previous version of the review. Eleven experimental studies allocated a total of 1795 participants to either green tea extract or placebo, all demonstrating an overall high methodological quality based on 'Risk of bias' assessment. For incident prostate cancer, the summary risk ratio (RR) in the green tea-supplemented participants was 0.50 (95% confidence interval (CI) 0.18 to 1.36), based on three studies and involving 201 participants (low-certainty evidence). The summary RR for gynaecological cancer was 1.50 (95% CI 0.41 to 5.48; 2 studies, 1157 participants; low-certainty evidence). No evidence of effect of non-melanoma skin cancer emerged (summary RR 1.00, 95% CI 0.06 to 15.92; 1 study, 1075 participants; low-certainty evidence). In addition, adverse effects of green tea extract intake were reported, including gastrointestinal disorders, elevation of liver enzymes, and, more rarely, insomnia, raised blood pressure and skin/subcutaneous reactions. Consumption of green tea extracts induced a slight improvement in quality of life, compared with placebo, based on three experimental studies. In nonexperimental studies, we included over 1,100,000 participants from 46 cohort studies and 85 case-control studies, which were on average of intermediate to high methodological quality based on Newcastle-Ottawa Scale 'Risk of bias' assessment. When comparing the highest intake of green tea with the lowest, we found a lower overall cancer incidence (summary RR 0.83, 95% CI 0.65 to 1.07), based on three studies, involving 52,479 participants (low-certainty evidence). Conversely, we found no association between green tea consumption and cancer-related mortality (summary RR 0.99, 95% CI 0.91 to 1.07), based on eight studies and 504,366 participants (low-certainty evidence). For most of the site-specific cancers we observed a decreased RR in the highest category of green tea consumption compared with the lowest one. After stratifying the analysis according to study design, we found strongly conflicting results for some cancer sites: oesophageal, prostate and urinary tract cancer, and leukaemia showed an increased RR in cohort studies and a decreased RR or no difference in case-control studies. AUTHORS' CONCLUSIONS Overall, findings from experimental and nonexperimental epidemiological studies yielded inconsistent results, thus providing limited evidence for the beneficial effect of green tea consumption on the overall risk of cancer or on specific cancer sites. Some evidence of a beneficial effect of green tea at some cancer sites emerged from the RCTs and from case-control studies, but their methodological limitations, such as the low number and size of the studies, and the inconsistencies with the results of cohort studies, limit the interpretability of the RR estimates. The studies also indicated the occurrence of several side effects associated with high intakes of green tea. In addition, the majority of included studies were carried out in Asian populations characterised by a high intake of green tea, thus limiting the generalisability of the findings to other populations. Well conducted and adequately powered RCTs would be needed to draw conclusions on the possible beneficial effects of green tea consumption on cancer risk.
2.
Mechanisms Underlying the Anti-Depressive Effects of Regular Tea Consumption.
Rothenberg, DO, Zhang, L
Nutrients. 2019;11(6)
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Previous research suggests that tea consumption is linked to a lower risk of depression, but it is not understood why. This meta-analysis and literature review looked at previous human, animal and laboratory studies that might give an indication of the mechanisms by which drinking tea can lead to a reduced depression risk. Tea contains many different active compounds such as L-theanine, various polyphenols and polyphenol metabolites that have effects on the immune system, stress response, brain neurotransmitters such as serotonin and dopamine, and gut bacteria. Different types of tea such as black, green or oolong tea contain different amounts of active compounds. The authors found that these compounds are capable of functioning through multiple pathways simultaneously that together reduce the risk of depression. The authors concluded that daily consumption of moderate amounts of different types of tea may offer significant potential benefit in the risk reduction of depression.
Abstract
This article is a comprehensive review of the literature pertaining to the antidepressant effects and mechanisms of regular tea consumption. Meta-data supplemented with recent observational studies were first analyzed to assess the association between tea consumption and depression risk. The literature reported risk ratios (RR) were 0.69 with 95% confidence intervals of 0.62-0.77. Next, we thoroughly reviewed human trials, mouse models, and in vitro experiments to determine the predominant mechanisms underlying the observed linear relationship between tea consumption and reduced risk of depression. Current theories on the neurobiology of depression were utilized to map tea-mediated mechanisms of antidepressant activity onto an integrated framework of depression pathology. The major nodes within the network framework of depression included hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, inflammation, weakened monoaminergic systems, reduced neurogenesis/neuroplasticity, and poor microbiome diversity affecting the gut-brain axis. We detailed how each node has subsystems within them, including signaling pathways, specific target proteins, or transporters that interface with compounds in tea, mediating their antidepressant effects. A major pathway was found to be the ERK/CREB/BDNF signaling pathway, up-regulated by a number of compounds in tea including teasaponin, L-theanine, EGCG and combinations of tea catechins and their metabolites. Black tea theaflavins and EGCG are potent anti-inflammatory agents via down-regulation of NF-κB signaling. Multiple compounds in tea are effective modulators of dopaminergic activity and the gut-brain axis. Taken together, our findings show that constituents found in all major tea types, predominantly L-theanine, polyphenols and polyphenol metabolites, are capable of functioning through multiple pathways simultaneously to collectively reduce the risk of depression.
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Dietary Strategies Implicated in the Prevention and Treatment of Metabolic Syndrome.
de la Iglesia, R, Loria-Kohen, V, Zulet, MA, Martinez, JA, Reglero, G, Ramirez de Molina, A
International journal of molecular sciences. 2016;17(11)
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Metabolic Syndrome (MetS) affects between 10-50% of adults worldwide and incidence continues to rise. MetS refers to a cluster of metabolic disturbances including central obesity, blood sugar imbalance, insulin resistance, high blood pressure and high cholesterol. Many dietary approaches have been studied to help improve MetS and this review evaluates how effective they are. It found that restricting calories helps promote weight loss and reduce inflammatory markers. Diets high in omega 3 fatty acids may play a moderate role in ameliorating inflammation. A low glycaemic approach helps support better blood sugar control and insulin response, by focusing on the quality of carbohydrate foods in the diet and favouring those lower in natural sugars which are absorbed more slowly. A high antioxidant diet helps reduce oxidative stress in MetS. A moderate to high protein diet helps improve satiety and support blood sugars, and cholesterol levels. Increasing protein intake works well as part of a restricted calorie diet. The Mediterranean diet, which is naturally rich in fibre, oil olive, fish, legumes, nuts and seeds is seen to support weight loss and reduce the risk of cardiovascular disease and Type II diabetes. There is no strong evidence to support increasing meal frequency to eat more, smaller meals throughout the day and spread calories. The review also looks at specific nutritional bioactive compounds: vitamin C, resveratrol, quercetin and others, with the aim of helping further clinical studies to find easy to follow therapies for MetS.
Abstract
Metabolic syndrome (MetS) is established as the combination of central obesity and different metabolic disturbances, such as insulin resistance, hypertension and dyslipidemia. This cluster of factors affects approximately 10%-50% of adults worldwide and the prevalence has been increasing in epidemic proportions over the last years. Thus, dietary strategies to treat this heterogenic disease are under continuous study. In this sense, diets based on negative-energy-balance, the Mediterranean dietary pattern, n-3 fatty acids, total antioxidant capacity and meal frequency have been suggested as effective approaches to treat MetS. Furthermore, the type and percentage of carbohydrates, the glycemic index or glycemic load, and dietary fiber content are some of the most relevant aspects related to insulin resistance and impaired glucose tolerance, which are important co-morbidities of MetS. Finally, new studies focused on the molecular action of specific nutritional bioactive compounds with positive effects on the MetS are currently an objective of scientific research worldwide. The present review summarizes some of the most relevant dietary approaches and bioactive compounds employed in the treatment of the MetS to date.
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Could gestational diabetes mellitus be managed through dietary bioactive compounds? Current knowledge and future perspectives.
Santangelo, C, Zicari, A, Mandosi, E, Scazzocchio, B, Mari, E, Morano, S, Masella, R
The British journal of nutrition. 2016;115(7):1129-44
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Gestational diabetes mellitus (GDM) is the most common metabolic disorder during pregnancy. Women with GDM are at a high risk of developing type 2 diabetes (T2D) later in life. Moreover, uncontrolled GDM is linked with a detrimental intra-uterine environment, which leads to foetal complications and an increased risk for the child of developing obesity and metabolic disorders. The aim of the review is to examine the current knowledge and issues about the impact of dietary polyphenols on the mechanisms and/or factors regulating glucose homeostasis, inflammation and adipose tissue function in metabolic alterations linked with GDM. Moreover, this study also reviews the role of Omega-3 fatty acids in pregnancy. The study is a descriptive review based on several studies. Literature data is mainly derived from in vitro and animal models. In vitro and animal studies show that almost all subclasses of flavonoids, stilbene RSV and some olive oil phenolic compounds, interact and modulate several molecular pathways regulating insulin. Obesity worsens GDM with increased risk of developing metabolic disorders in both mother and offspring later in life. The adoption of healthy lifestyle, with adherence to a healthy dietary pattern, has positive effects on the prevention and management of diabetes.
Abstract
Gestational diabetes mellitus (GDM) is a serious problem growing worldwide that needs to be addressed with urgency in consideration of the resulting severe complications for both mother and fetus. Growing evidence indicates that a healthy diet rich in fruit, vegetables, nuts, extra-virgin olive oil and fish has beneficial effects in both the prevention and management of several human diseases and metabolic disorders. In this review, we discuss the latest data concerning the effects of dietary bioactive compounds such as polyphenols and PUFA on the molecular mechanisms regulating glucose homoeostasis. Several studies, mostly based on in vitro and animal models, indicate that dietary polyphenols, mainly flavonoids, positively modulate the insulin signalling pathway by attenuating hyperglycaemia and insulin resistance, reducing inflammatory adipokines, and modifying microRNA (miRNA) profiles. Very few data about the influence of dietary exposure on GDM outcomes are available, although this approach deserves careful consideration. Further investigation, which includes exploring the 'omics' world, is needed to better understand the complex interaction between dietary compounds and GDM.
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Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial.
Matsumoto, K, Yamada, H, Takuma, N, Niino, H, Sagesaka, YM
BMC complementary and alternative medicine. 2011;11:15
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Influenza infection is the main cause of acute respiratory illnesses worldwide with limited prevention and treatment options. Pre-clinical experiments have shown that green tea catechins can prevent influenza infection in vitro, but clinical evidence has not been conclusive. The aim of this randomised, double-blind study was to evaluate the clinical efficacy of two compounds from green tea, catechins and theanine, in preventing influenza infection. 196 participants completed the 5 months study. The incidence of clinically defined influenza infections was significantly lower in the catechin/theanine group than in the placebo group. The incidence of laboratory-confirmed influenza infection was also lower in the catechin/theanine group than in the placebo group, but this difference was not statistically significant. No serious adverse events were observed in either group. The occurrence of mild symptoms, such as bloating and constipation, did not significantly differ between the two groups. The authors concluded that the effectiveness of catechin/theanine in this trial might be underestimated due to methodological limitations and that larger scale randomised trials are needed to confirm the effectiveness of catechin/theanine to prevent laboratory-confirmed influenza infection.
Abstract
BACKGROUND Experimental studies have revealed that green tea catechins and theanine prevent influenza infection, while the clinical evidence has been inconclusive. This study was conducted to determine whether taking green tea catechins and theanine can clinically prevent influenza infection. METHODS DESIGN, SETTING, AND PARTICIPANTS A randomized, double-blind, placebo-controlled trial of 200 healthcare workers conducted for 5 months from November 9, 2009 to April 8, 2010 in three healthcare facilities for the elderly in Higashimurayama, Japan. INTERVENTIONS The catechin/theanine group received capsules including green tea catechins (378 mg/day) and theanine (210 mg/day). The control group received placebo. MAIN OUTCOME MEASURES The primary outcome was the incidence of clinically defined influenza infection. Secondary outcomes were (1) laboratory-confirmed influenza with viral antigen measured by immunochromatographic assay and (2) the time for which the patient was free from clinically defined influenza infection, i.e., the period between the start of intervention and the first diagnosis of influenza infection, based on clinically defined influenza infection. RESULTS Eligible healthcare workers (n = 197) were enrolled and randomly assigned to an intervention; 98 were allocated to receive catechin/theanine capsules and 99 to placebo. The incidence of clinically defined influenza infection was significantly lower in the catechin/theanine group (4 participants; 4.1%) compared with the placebo group (13 participants; 13.1%) (adjusted OR, 0.25; 95% CI, 0.07 to 0.76, P = 0.022). The incidence of laboratory-confirmed influenza infection was also lower in the catechin/theanine group (1 participant; 1.0%) than in the placebo group (5 participants; 5.1%), but this difference was not significant (adjusted OR, 0.17; 95% CI, 0.01 to 1.10; P = 0.112). The time for which the patient was free from clinically defined influenza infection was significantly different between the two groups (adjusted HR, 0.27; 95% CI, 0.09 to 0.84; P = 0.023). CONCLUSIONS Among healthcare workers for the elderly, taking green tea catechins and theanine may be effective prophylaxis for influenza infection. TRIAL REGISTRATION ClinicalTrials (NCT): NCT01008020.