Tea consumption and risk of type 2 diabetes: a meta-analysis of cohort studies.
ABSTRACT: BACKGROUND: Tea consumption has been extensively studied in relation to various diseases, several epidemiologic studies have been performed to investigate the association of tea consumption with type 2 diabetes; however, the results of these studies were not entirely consistent. OBJECTIVE: To conduct a meta-analysis of studies that assessed the association of tea consumption and the risk of type 2 diabetes. RESEARCH DESIGN AND METHODS: We performed a systematic literature search through November 2008 in PUBMED, MEDLINE, EMBASE, and Cochrane Database of Systematic Reviews. The search was limited to English-language studies. Studies were excluded if they were type 1 diabetes, animal studies. Nine cohort studies were identified by two authors, and summary relative risks (RRs) were calculated using a random-effects model. RESULTS: We identified nine cohort studies, including 324,141 participants and 11,400 incident cases of type 2 diabetes with follow-up ranging from 5 to 18 years. The summary adjusted RR did not show that tea consumption was associated with a reduced type 2 diabetes risk (RR, 0.96; 95% confidence interval (CI), 0.92-1.01). Evidence from the results of our stratified analyses revealed that tea consumption > or =4 cups per day (RR, 0.8; 95% CI, 0.7-0.93) might play a role in the prevention of type 2 diabetes. However, no statistically significant association was observed for sex and the follow-up durations stratified between tea consumption and type 2 diabetes. CONCLUSIONS: This meta-analysis indicates that tea consumption > or =4 cups per day may lower the risk of type 2 diabetes.
Project description:Tea has been suggested to decrease blood glucose levels and protect pancreatic ? cells in diabetic mice. However, human epidemiological studies showed inconsistent results for the association between tea consumption and type 2 diabetes mellitus (T2DM) risk. The aim of this study was to conduct a meta-analysis to further explore the association between tea consumption and incidence of T2DM.Systematic review and meta-analysis.We performed a systematic literature search up to 30 August 2013 in PubMed, EMBASE, Chinese Wanfang Database and CNKI database. Pooling relative risks (RRs) were estimated by random-effect models. Two kinds of subgroup analyses (according to sex and regions) were performed. Sensitive analyses were performed according to types of tea.Overall, no statistically significant relationship between tea consumption and risk of T2DM was found based on 12 eligible studies (pooling RR 0.99, 95% CI 0.95 to 1.03). Compared with the lowest/non-tea group, daily tea consumption (?3 cups/day) was associated with a lower T2DM risk (RR 0.84, 95% CI 0.73 to 0.97). Subgroup analyses showed a difference between men and women. Overall, the RRs (95% CI) were 0.92 (0.84 to 1.00) for men, and 1.00 (0.96 to 1.05) for women, respectively. Tea consumption of ?3 cups/day was associated with decreased T2DM risk in women (RR 0.84, 95% CI 0.71 to 1.00). Overall, the RRs (95% CIs) were 0.84 (0.71 to 1.00) for Asians, and 1.00 (0.97 to 1.04) for Americans and Europeans, respectively. No obvious change was found in sensitivity analyses.The results suggest that daily tea consumption (?3 cups/day) is associated with a lower T2DM risk. However, further studies are needed to enrich related evidence, especially with regard to types of tea or sex.
Project description:<h4>Objective</h4>Coffee and tea consumption is associated with a decreased type 2 diabetes risk in non-pregnant adults. We examined the relation between first trimester coffee and tea consumption and gestational diabetes mellitus (GDM) risk.<h4>Design</h4>Population-based cohort study.<h4>Setting</h4>Denmark 1996-2002.<h4>Population</h4>Non-diabetic women with singleton pregnancies in the Danish National Birth Cohort (n = 71,239).<h4>Methods</h4>Estimated adjusted relative risks (RR) and 95% confidence intervals (95%CI) for the association between first trimester coffee and tea or estimated total caffeine and GDM.<h4>Main outcome measures</h4>GDM ascertained from the National Hospital Discharge Register or maternal interview.<h4>Results</h4>Coffee or tea intake was reported in 81.2% (n = 57,882) and 1.3% (n = 912) of pregnancies were complicated by GDM. Among non-consumers, 1.5% of pregnancies were complicated by GDM. Among coffee drinkers, GDM was highest among women who drank ?8 cups/day (1.8%) with no significant difference across intake levels (P = 0.10). Among tea drinkers, there was no difference in GDM across intake levels (1.2%; P = 0.98). After adjustment for age, socio-occupational status, parity, pre-pregnancy body mass index, smoking, and cola, there was suggestion of a protective, but non-significant association with increasing coffee (RR ?8 versus 0 cups/day = 0.89 [95%CI 0.64-1.25]) and tea (RR ?8 versus 0 cups/day = 0.77 [95%CI 0.55-1.08]). Results were similar by smoking status, except a non-significant 1.45-fold increased risk with ?8 coffee cups/day for non-smokers. There was a non-significant reduced GDM risk with increasing total caffeine.<h4>Conclusions</h4>Our results suggest that moderate first trimester coffee and tea intake were not associated with GDM increased risk and possibly may have a protective effect.
Project description:BACKGROUND: We conducted a dose-response meta-analysis of prospective studies to summarize evidence of the association between tea consumption and the risk of breast, colorectal, liver, prostate, and stomach cancer. METHODS: We searched PubMed and two other databases. Prospective studies that reported risk ratios (RRs) with 95% confidence intervals (CIs) of cancer risk for ?3 categories of tea consumption were included. We estimated an overall RR with 95% CI for an increase of three cups/day of tea consumption, and, usingrestricted cubic splines, we examined a nonlinear association between tea consumption and cancer risk. RESULTS: Forty-one prospective studies, with a total of 3,027,702 participants and 49,103 cancer cases, were included. From the pooled overall RRs, no inverse association between tea consumption and risk of five major cancers was observed. However, subgroup analysis showed that increase in consumption of three cups of black tea per day was a significant risk factor for breast cancer (RR, 1.18; 95% CI, 1.05-1.32). CONCLUSION: Ourresults did not show a protective role of tea in five major cancers. Additional large prospective cohort studies are needed to make a convincing case for associations.
Project description:Coffee and tea consumption has been associated with a lower type 2 diabetes risk but little is known about how changes in coffee and tea consumption influence subsequent type 2 diabetes risk. We examined the associations between 4 year changes in coffee and tea consumption and risk of type 2 diabetes in the subsequent 4 years.We prospectively followed 48,464 women in the Nurses' Health Study (NHS; 1986-2006), 47,510 women in NHS II (1991-2007) and 27,759 men in the Health Professionals Follow-up Study (HPFS; 1986-2006). Diet was assessed every 4 years using a validated food-frequency questionnaire. Self-reported cases of incident type 2 diabetes were validated by supplementary questionnaires.During 1,663,319 person-years of follow-up, we documented 7,269 cases of incident type 2 diabetes. Participants who increased their coffee consumption by more than 1 cup/day (median change?=?1.69 cups/day) over a 4 year period had an 11% (95% CI 3%, 18%) lower risk of type 2 diabetes in the subsequent 4 years compared with those who made no changes in consumption. Participants who decreased their coffee intake by more than 1 cup/day (median change?=?-2 cups/day) had a 17% (95% CI 8%, 26%) higher risk for type 2 diabetes. Changes in tea consumption were not associated with type 2 diabetes risk.Our data provide novel evidence that increasing coffee consumption over a 4 year period is associated with a lower risk of type 2 diabetes, while decreasing coffee consumption is associated with a higher risk of type 2 diabetes in subsequent years.
Project description:Previous meta-analyses identified an inverse association of coffee consumption with the risk of type 2 diabetes. However, an updated meta-analysis is needed because new studies comparing the trends of association for caffeinated and decaffeinated coffee have since been published.PubMed and Embase were searched for cohort or nested case-control studies that assessed the relationship of coffee consumption and risk of type 2 diabetes from 1966 to February 2013. A restricted cubic spline random-effects model was used.Twenty-eight prospective studies were included in the analysis, with 1,109,272 study participants and 45,335 cases of type 2 diabetes. The follow-up duration ranged from 10 months to 20 years. Compared with no or rare coffee consumption, the relative risk (RR; 95% CI) for diabetes was 0.92 (0.90-0.94), 0.85 (0.82-0.88), 0.79 (0.75-0.83), 0.75 (0.71-0.80), 0.71 (0.65-0.76), and 0.67 (0.61-0.74) for 1-6 cups/day, respectively. The RR of diabetes for a 1 cup/day increase was 0.91 (0.89-0.94) for caffeinated coffee consumption and 0.94 (0.91-0.98) for decaffeinated coffee consumption (P for difference = 0.17).Coffee consumption was inversely associated with the risk of type 2 diabetes in a dose-response manner. Both caffeinated and decaffeinated coffee was associated with reduced diabetes risk.
Project description:Coffee consumption has been inversely associated with type 2 diabetes risk, but its mechanisms are largely unknown. We aimed to examine whether plasma levels of sex hormones and sex hormone-binding globulin (SHBG) may account for the inverse association between coffee consumption and type 2 diabetes risk.We conducted a case-control study nested in the prospective Women's Health Study (WHS). During a median follow-up of 10 years, 359 postmenopausal women with newly diagnosed type 2 diabetes were matched with 359 control subjects by age, race, duration of follow-up, and time of blood draw.Caffeinated coffee was positively associated with SHBG but not with sex hormones. Multivariable-adjusted geometric mean levels of SHBG were 26.6 nmol/l among women consuming ?4 cups/day of caffeinated coffee and 23.0 nmol/l among nondrinkers (P for trend = 0.01). In contrast, neither decaffeinated coffee nor tea was associated with SHBG or sex hormones. The multivariable-adjusted odds ratio (OR) of type 2 diabetes for women consuming ?4 cups/day of caffeinated coffee compared with nondrinkers was 0.47 (95% CI 0.23-0.94; P for trend = 0.047). The association was largely attenuated after further adjusting for SHBG (OR 0.71 [95% CI 0.31-1.61]; P for trend = 0.47). In addition, carriers of rs6259 minor allele and noncarriers of rs6257 minor allele of SHBG gene consuming ?2 cups/day of caffeinated coffee had lower risk of type 2 diabetes in directions corresponding to their associated SHBG.Our findings suggest that SHBG may account for the inverse association between coffee consumption and type 2 diabetes risk among postmenopausal women.
Project description:Laboratorial and epidemiological researches suggested that tea exhibited potential neuroprotective effect which may prevent cognitive impairment, but there were few data among the elderly aged 60 years and above in China.The objective was to explore the relationship between characteristics of tea consumption and cognitive impairment.We analyzed the baseline data from Zhejiang Major Public Health Surveillance Program (ZPHS) which was conducted in 2014. Totally 9,375 residents aged 60 years and above were recruited in this study. Face-to-face interview based on a self-developed questionnaire was performed for each participant. Detailed tea consumption habits were included in the questionnaire. Cognitive impairment screening was performed by using Mini-Mental State Examination (MMSE). Education-specific cut-off points for Chinese were applied to determine the status of cognitive impairment. Logistic regression analysis was used to calculate odds ratios (ORs) of cognitive impairment associated with tea consumption.The means (SD) of MMSE scores for the subjects who did not consume tea and consumed <2 cups/d, 2-4 cups/d, ≥4 cups/d were 23.3 (SD = 5.61), 23.8 (SD = 5.60), 24.5 (SD = 5.63) and 25.0 (SD = 5.08), respectively. An inverse correlation was found between tea consumption (of all types) and prevalence of cognitive impairment. Volume of tea consumption was significantly associated with cognitive impairment: compared with non-consumption participants, those who consumed < 2 cups/d, 2-4 cups/d, and ≥4 cups/d were observed ORs of 0.77 (95% CI: 0.56, 1.07), 0.62 (95% CI: 0.47, 0.81), and 0.49 (95% CI: 0.36, 0.66), respectively. Compared with non-consumption, black tea presented a positive correlation with cognitive function after controlling for potential confounders (OR = 0.52, 95% CI: 0.28, 0.95), while green tea showed no significant difference (OR = 1.04, 95% CI: 0.72, 1.51). Participants who consumed weak tea, moderate tea or strong tea more often were observed a better cognitive status when compared with those who did not have tea, with an OR of 0.51 (95% CI: 0.28, 0.92), 0.32 (95% CI: 0.19, 0.56) and 0.42 (95% CI: 0.22, 0.78) after adjusting for the potential confounders. But there was no statistically significant difference between any two of these ORs.Black tea consumption was association with better cognitive performance among the elderly aged 60 years and above in China, while green tea presented no correlation. The positive association of cognitive status with tea consumption was not limited to particular type of concentration.
Project description:Higher coffee consumption has been associated with a lower risk of type 2 diabetes in cohort studies, but the physiological pathways through which coffee affects glucose metabolism are not fully understood. The aim of this study was to evaluate the associations between habitual coffee and tea consumption and glucose metabolism in a multi-ethnic Asian population and possible mediation by inflammation.We cross-sectionally examined the association between coffee, green tea, black tea and Oolong tea consumption and glycemic (fasting plasma glucose, HOMA-IR, HOMA-beta, plasma HbA1c) and inflammatory (plasma adiponectin and C-reactive protein) markers in a multi-ethnic Asian population (N = 4139).After adjusting for multiple confounders, we observed inverse associations between coffee and HOMA-IR (percent difference: - 8.8% for ? 3 cups/day versus rarely or never; Ptrend = 0.007), but no significant associations between coffee and inflammatory markers. Tea consumption was not associated with glycemic markers, but green tea was inversely associated with plasma C-reactive protein concentrations (percent difference: - 12.2% for ? 1 cup/day versus < 1 cup/week; Ptrend = 0.042).These data provide additional evidence for a beneficial effect of habitual caffeinated coffee consumption on insulin sensitivity, and suggest that this effect is unlikely to be mediated by anti-inflammatory mechanisms.
Project description:Laboratory studies have observed chemopreventive effects of black and green tea on breast cancer development, but few epidemiologic studies have identified such effects. We investigated the association between tea consumption and breast cancer risk using data from 45,744?U.S. and Puerto Rican women participating in the Sister Study. Frequency and serving size of black and green tea consumption were measured at cohort enrollment. Breast cancer diagnoses were reported during follow-up and confirmed by medical record review. Multivariable Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI). We further investigated potential variation according to estrogen receptor (ER) status, menopausal status and body mass index (BMI). Overall, 81.6 and 56.0% of women drank black or green tea, respectively. A total of 2,809 breast cancer cases were identified in the cohort. The multivariable model suggested an inverse association between black (?5 vs. 0 cups/week: HR = 0.88, 95% CI 0.78, 1.00, p-trend = 0.08) and green tea (?5 vs. 0 cups/week: HR = 0.82, 95% CI 0.70, 0.95, p-trend?<?0.01) consumption and breast cancer risk. We did not observe differences by ER characteristics, menopausal status or BMI. In conclusion, our study suggests drinking at least five cups of green or black tea per week may be associated with decreased breast cancer risk.
Project description:OBJECTIVES: This updated meta-analysis was conducted to assess the association between coffee consumption and breast cancer risk. METHODS: We conducted a systematic search updated July 2012 to identify observational studies providing quantitative estimates for breast cancer risk in relation to coffee consumption. Pooled relative risks (RRs) with 95% confidence intervals (CIs) were calculated using a random-effects model, and generalized least square trend estimation was used to assess dose-response relationships. RESULTS: A total of 26 studies (16 cohort and 10 case-control studies) on coffee intake with 49497 breast cancer cases were included in the meta-analysis. The pooled RR showed a borderline significant influence of highest coffee consumption (RR = 0.96; 95% CI 0.93-1.00), low-to moderate coffee consumption (RR = 0.99; 95% CI 0.95-1.04), or an increment of 2 cups/day of coffee consumption (RR = 0.98; 95% CI 0.97-1.00) on the risk of breast cancer. In stratified analysis, a significant inverse association was observed in ER-negative subgroup. However, no significant association was noted in the others. CONCLUSIONS: Our findings suggest that increased coffee intake is not associated with a significantly reduced risk of breast cancer, but we observe an inverse association in ER-negative subgroup analysis. More large studies are needed to determine subgroups to obtain more valuable data on coffee drinking and breast cancer risk.