Habitual green tea consumption and risk of an aneurysmal rupture subarachnoid hemorrhage: A case–control study in Nagoya, Japan

Causal Association between Tea Intake and Acute Cerebrovascular Events: A Multivariate Mendelian Randomized Study in European Populations

BACKGROUND

Numerous research works have investigated the association between tea consumption and the risk of acute cerebrovascular events; however, the results are inconsistent.

OBJECTIVES

We used Mendelian randomization (MR) to evaluate the causal association between tea intake and several acute cerebrovascular events, including any ischemic stroke, large atherosclerotic stroke (LAS), cardiogenic embolic stroke (CES), small vessel stroke (SVS), intracranial hemorrhage (ICH), and subarachnoid hemorrhage (SAH).

METHODS

We obtained summary genome-wide association study (GWAS) data on tea intake and acute cerebrovascular events in populations of European ancestry. The GWAS on tea intake is derived from the UK Biobank, where we have chosen single-nucleotide polymorphisms (SNPs) closely associated with it as instrumental variables. We also obtained summary data on ischemic stroke from a GWAS meta-analysis, as well as summary data on ICH and SAH from the FinnGen study. We first explored the causal association between tea intake and several acute cerebrovascular events using univariate Mendelian randomization (UVMR), and then further assessed the causal association between tea intake and SVS using multivariate Mendelian randomization (MVMR) corrected for multiple confounders.

RESULTS

In UVMR, genetically predicted increases in tea intake were linked to a lower risk of SVS (OR: 0.58; 95% CI: 0.39, 0.86). There was no causal association between tea intake and the risk of other acute cerebrovascular events. In the MVMR, our results show that there was still a significant causal association between drinking tea and SVS, after adjusting body mass index, total cholesterol, low-density lipoprotein cholesterol, diabetes, hypertension, smoking, and alcohol consumption.

CONCLUSION

This MR study provides new genetic evidence that increased tea intake reduces the risk of SVS in the European population. However, possibly because of limited statistical power, the study did not find that tea consumption reduced the risk of several other acute cerebrovascular events.

Genetically predicted coffee and tea consumption and risk of intracranial aneurysm

OBJECTIVES

Observational studies have shown associations between coffee and tea consumption and risk of intracranial aneurysm (IA). However, the results are not consistent. We conducted a Mendelian randomization study to clarify whether genetically predicted coffee and tea consumption has a causal effect on IA and its subtypes.

METHODS

Genetic variants associated with coffee and tea consumption (cups/day) were obtained from large genome-wide association studies (GWASs), up to 349,376 subjects. Summary-level data for IA were adopted from a GWAS in 79,429 subjects (23 cohorts, 7495 cases, and 71,934 controls).

RESULTS

Genetically predicted coffee consumption was associated with a higher risk of any IA and aneurysmal subarachnoid hemorrhage (SAH), but not with unruptured IA. The ORs per 1 cup/day increase in genetically predicted coffee consumption were 1.42 (95% CI: 1.09-1.86; P = 0.010) for IA, 1.51 (95% CI: 1.13-2.03; P = 0.005) for aneurysmal SAH, and 1.20 (95% CI: 0.74-1.96; P = 0.460) for unruptured IA. Genetically predicted tea consumption was not associated with risk of any IA and its subtypes (P > 0.05). The associations remained consistent in sensitivity analyses, and no evidence of pleiotropy was detected.

CONCLUSIONS

Our study provides evidence to support that coffee consumption may increase the risk of IA and associated hemorrhage. Coffee should be limited for those at high risk of IA and associated hemorrhage.

Green tea consumption and the risk of stroke: A systematic review and meta-analysis of cohort studies

OBJECTIVES

Epidemiologic studies are inconsistent regarding the association between green tea consumption and the risk of stroke. We performed a meta-analysis to determine whether an association exists between them in cohort studies.

METHODS

We searched the PubMed and Embase databases for studies conducted from 1966 through September 2022. Prospective cohort studies that provided relative risk (RR) estimates with 95% confidence interval (CI)s for the association were included. Study-specific risk estimates were combined by using a random-effects model.

RESULTS

A total of five studies, with 11 421 stroke cases among 645 393 participants, were included in the meta-analysis. The summary RR indicated a significant association between highest green tea consumption and reduced risk of stroke (summary RR: 0.74; 95% CI, 0.66-0.83). In the dose-response analysis, we observed a nonlinear association between green tea consumption and the risk of stroke (P for nonlinearity = 0.0000). Compared with non-consumers, the RRs (95% CI) of stroke across levels of green tea consumption were 0.91 (0.89-0.94) for 150 mL/d, 0.84 (0.80-0.89) for 300 mL/d, 0.79 (0.74-0.84) for 500 mL/d, 0.77 (0.72-0.82) for 900 mL/d, and 0.84 (0.77-0.91) for 1500 mL/d.

CONCLUSIONS

This meta-analysis suggests that green tea consumption is inversely associated with the risk of stroke, especially among those with moderate consumption. Our results support recommendations for green tea consumption to the primary prevention of stroke.

Tea consumption and cerebral hemorrhage risk: a meta-analysis

BACKGROUND

Tea contains many polyphenols with biological properties such as antithrombosis and antioxidation. Recent observational studies on tea consumption concerning cerebral hemorrhage risk have reported inconsistent results. This meta-analysis aimed to summarize the accumulated evidence on the association between tea consumption and cerebral hemorrhage risk.

METHODS

Web of Science, PubMed, Embase, and Scopus databases were searched to identify relevant studies through December 2021. Relative risks (RRs) or odds ratios (ORs) from observational studies were synthesized.

RESULTS

Ten studies involving over 721,827 participants were included. Higher tea consumption was correlated with a 23% (RR = 0.77; 95% CI 0.66-0.89) lower risk of cerebral hemorrhage. Subgroup meta-analyses indicated higher tea consumption was beneficial in preventing cerebral hemorrhage risk for green tea, alcohol-adjusted, fruit/vegetables-adjusted, and physical activity-adjusted subgroups, respectively (P < 0.01). Dose-response analysis indicated each one-cup (120 ml/cup) increment in tea or green tea intake/day was correlated with an average of 2% (RR = 0.98, 95% CI 0.976-0.990), or 6% (RR = 0.94; 95% CI 0.92-0.97) lower cerebral hemorrhage risk.

CONCLUSIONS

This study suggests that daily tea consumption is related to a lower risk of cerebral hemorrhage among adults. Green tea consumption appears to be more beneficial in preventing cerebral hemorrhage. Physical activity, fruit/vegetables, and alcohol may affect the relationship between tea consumption and hemorrhagic stroke. Future studies should investigate the interplay of tea with these factors.

Tea consumption and cardiovascular disease risk

BACKGROUND

The present analysis was conducted in response to inconsistent epidemiologic studies on the relation between consumption of tea and cardiovascular diseases.

OBJECTIVE

We undertook a literature review of the consistency and strength of the associations between tea and cardiovascular diseases on the basis of published observational studies and meta-analyses addressing tea or tea flavonoids and cardiovascular disease risk.

DESIGN

We performed a search in 3 databases for meta-analyses and compared them with studies they subsumed. We performed an additional search for subsequent studies to determine whether the conclusions were consistent.

RESULTS

Many epidemiologic studies have been conducted and summarized in 5 meta-analyses on either tea consumption or flavonoid consumption and cardiovascular disease or the subset of stroke. Heterogeneity of effect was seen when the outcome included all cardiovascular diseases. In the case of stroke, a consistent, dose-response association with tea consumption on both incidence and mortality was noted with RRs of 0.80 (95% CI: 0.65, 0.98) for flavonoids and 0.79 (95% CI: 0.73, 0.85) for tea when high and low intakes were compared or the addition of 3 cups/d was estimated.

CONCLUSION

Thus, the strength of this evidence supports the hypothesis that tea consumption might lower the risk of stroke.

The role of oxidative stress in cerebral aneurysm formation and rupture

Oxidative stress is known to contribute to the progression of cerebrovascular disease. Additionally, oxidative stress may be increased by, but also augment inflammation, a key contributor to cerebral aneurysm development and rupture. Oxidative stress can induce important processes leading to cerebral aneurysm formation including direct endothelial injury as well as smooth muscle cell phenotypic switching to an inflammatory phenotype and ultimately apoptosis. Oxidative stress leads to recruitment and invasion of inflammatory cells through upregulation of chemotactic cytokines and adhesion molecules. Matrix metalloproteinases can be activated by free radicals leading to vessel wall remodeling and breakdown. Free radicals mediate lipid peroxidation leading to atherosclerosis and contribute to hemodynamic stress and hypertensive pathology, all integral elements of cerebral aneurysm development. Preliminary studies suggest that therapies targeted at oxidative stress may provide a future beneficial treatment for cerebral aneurysms, but further studies are indicated to define the role of free radicals in cerebral aneurysm formation and rupture. The goal of this review is to assess the role of oxidative stress in cerebral aneurysm pathogenesis.

Can green tea do that? A literature review of the clinical evidence

OBJECTIVE

Habitual green tea consumption has long been associated with health benefits including chemoprevention and cardiovascular protection. This non-systematic literature review presents the clinical evidence to date.

METHOD

A literature review of peer-reviewed articles on observational and interventional studies was conducted to include green tea, its extract or its purified polyphenol (-)-epigallocatechin-3-gallate (EGCG). Electronic databases searched included PubMed (1966-2009) and the Cochrane Library (Issue 4, 2008).

RESULTS

Observational studies are inconclusive on the benefits of habitual consumption of green tea in the prevention of most cancers. However, there are trends towards prevention in breast and prostate cancers. Interventional studies have demonstrated reduction in relapses following surgical resection in colorectal adenomas and increased survival rates in epithelial ovarian cancer. Observational studies indicate that green tea may provide protection against hypertension and reduce the risk for stroke, and interventional studies are providing biochemical and physiological evidence.

CONCLUSION

Although the overall clinical evidence is inconclusive, habitual green tea consumption may be providing some level of chemoprevention in prostate and breast cancer. Green tea may also attenuate the risk factors association with the development of atherosclerosis thus reducing the incidence of cardiovascular events and stoke.

Green and black tea consumption and risk of stroke: a meta-analysis

BACKGROUND AND PURPOSE

Experimental models of stroke provide consistent evidence of smaller stroke volumes in animals ingesting tea components or tea extracts. To assess whether a similar association of black or green tea consumption with reduced risk is evident in human populations, we sought to identify and summarize all human clinical and observational data on tea and stroke.

METHODS

We searched PubMed and Web of Science for all studies on stroke and tea consumption in humans with original data, including estimation or measurement of tea consumption and outcomes of fatal or nonfatal stroke. Data from 9 studies involving 4378 strokes among 194 965 individuals were pooled. The main outcome was the occurrence of fatal or nonfatal stroke. We tested for heterogeneity and calculated the summary effect estimate associated with consumption of >or=3 cups of tea (green or black) per day using random-effects and fixed-effects models for the homogeneous studies. Publication bias was also evaluated.

RESULTS

Regardless of their country of origin, individuals consuming >or=3 cups of tea per day had a 21% lower risk of stroke than those consuming <1 cup per day (absolute risk reduction, 0.79; CI, 0.73 to 0.85). The proportion of heterogeneity not explained by chance alone was 23.8%.

CONCLUSIONS

Although a randomized clinical trial would be necessary to confirm the effect, this meta-analysis suggests that daily consumption of either green or black tea equaling 3 cups per day could prevent the onset of ischemic stroke.

Effects of green tea and EGCG on cardiovascular and metabolic health

Since ancient times green tea has been considered a health-promoting beverage. In recent years, scientists throughout the world have investigated the potential benefits of green tea and its most abundant catechin, epigallocatechin gallate (EGCG). The anti-cancer effects of green tea and EGCG were the focus of early research, and encouraging data from in vitro, animal model, and human studies have emerged. Due to the dominant role of cardiovascular disease and the dramatic rise of obesity and type 2 diabetes mellitus as major and interlinked healthcare problems, green tea and EGCG are increasingly being investigated in these areas. Dose-response relationships observed in several epidemiological studies have indicated that pronounced cardiovascular and metabolic health benefits can be obtained by regular consumption of 5-6 or more cups of green tea per day. Furthermore, intervention studies using similar amounts of green tea, containing 200-300 mg of EGCG, have demonstrated its usefulness for maintaining cardiovascular and metabolic health. Additionally, there are numerous in vivo studies demonstrating that green tea and EGCG exert cardiovascular and metabolic benefits in these model systems. Therefore, green tea and EGCG can be regarded as food components useful for the maintenance of cardiovascular and metabolic health. To prove the effectiveness for disease prevention or treatment, several multi-center, long-term clinical studies investigating the effects of one precisely-defined green tea product on cardiovascular and metabolic endpoints would be necessary. The aim of this manuscript is to provide an overview of the research investigating the effects of green tea and green tea catechins on cardiovascular and metabolic health.

Dietary antioxidant intake and risk of an aneurysmal rupture subarachnoid hemorrhage in Japan

The purpose of this study was to investigate the relationship between dietary antioxidant intake and the risk of subarachnoid hemorrhage (SAH) in a case-control study. An antioxidant intake score was calculated for individual values for each food group (soy products, green yellow-vegetables, fruits, boiled rice and tea) collected by a self-administered food frequency questionnaire. Incident SAH cases (n=201) were identified and individually matched for age (+/-2 years) and gender to community (n=201) controls from April 1992 to March 1997. The antioxidant intake score was inversely associated with the risk of SAH, even after adjusting for confounding factors (lowest vs highest score adjusted odds ratio, 0.54; 95% confidence interval, 0.30-0.99). These findings suggest that the development of SAH may be reduced by the frequent intake of various antioxidants in the diet. Prospective studies are needed to confirm the relationship of dietary antioxidants to SAH risk in Japanese men and women.