Tea consumption has inconsistently been shown to be associated with the risk of type 2 diabetes (T2D). The aim of the present study was to conduct a dose-response meta-analysis of cohort studies assessing the association between consumption of tea and risk of developing T2D. Pertinent studies were identified by searching PubMed, Web of Science and EMBASE through 31 March 2013. A total of sixteen cohorts from fifteen articles that reported 37 445 cases of diabetes among 545 517 participants were included. A significant linearly inverse association between tea consumption and T2D risk was found (P for linear trend¼0·02). An increase of 2 cups/d in tea consumption was found to be associated with a 4·6 (95 % CI 0·9, 8·1) % reduced risk of T2D. On the basis of the dose -response meta-analysis, the predicted relative risks of diabetes for 0, 1, 2, 3, 4, 5 and 6 cups of tea consumed per d were 1·00 (referent), 0·97 (95 % CI 0·94, 1·01), 0·95(95 % CI 0·92, 0·98), 0·93 (95 % CI 0·88, 0·98), 0·90 (95 % CI 0·85, 0·96), 0·88 (95 % CI 0·83, 0·93) and 0·85 (95 % CI 0·80, 0·91), respectively. There was a statistically significant heterogeneity within the selected studies (Q ¼ 45·32, P,0·001, I 2 ¼ 60·3 %). No evidence of substantial smallstudy bias was found (P¼0·46). Our findings suggest that tea consumption could be linearly inversely associated with T2D risk. Future well-designed observational studies that account for different characteristics of tea such as tea types, preparation methods and tea strength are needed to fully characterise such an association.Key words: Tea: Meta-analyses: Cohort studies: Type 2 diabetes Diabetes is one of the biggest public health challenges of the twenty-first century with increasing prevalence globally (1) . According to a report (2) released by the International Diabetes Federation, in 2012, more than 371 million people had diabetes, representing 8·3 % of the global adult population, while 4·8 million people died due to diabetes and more than 471 billion US$ were spent on health care for diabetes. Therefore, the primary prevention efforts towards diabetes should be explored.Several cohort studies (3 -18) have inconsistently shown that regular tea consumption may have a protective effect on type 2 diabetes (T2D). An earlier meta-analysis (19) that focused on tea consumption and T2D risk and combined results from nine cohort studies (10 -18) published before 2009 reported that the consumption of tea is not associated with a lower risk of T2D in individuals consuming large amounts compared with those consuming low amounts and that consuming $ 4 cups per d may lower the risk of T2D (relative risk (RR) 0·80, 95 % CI 0·70, 0·93), in which the conclusion was drawn on the basis of five studies in the secondary analysis. Furthermore, another meta-analysis of cohort studies carried out by Huxley et al. (20) published in the same year has concluded that consuming $3 or $4 cups of tea daily is associated with a 16 % reduced risk of T2D compared with not consuming tea. These investigations ...

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Evidence from observational studies on light at night (LAN) exposure, sleep duration, endogenous melatonin levels, and risk for breast cancer in women is conflicting. This led us to conduct a dose-response analysis of published observational data. Pertinent studies were identified by searching Medline, Web of Science, and EMBASE through April 2013. The dose-response relationship between sleep duration, urinary 6-sulphatoxymelatonin levels, and breast cancer was assessed using the restricted cubic spline model and by multivariate random-effects metaregression. A separate meta-analysis was also carried out to calculate the relative risks (RRs) with 95% confidence intervals (CIs) for breast cancer for the comparable categories or highest levels of exposure versus the lowest levels. Twelve case-control and four cohort studies were included in the analysis. High artificial LAN exposure is associated with an increased risk for breast cancer (RR=1.17, 95% CI: 1.11-1.23), but not ambient LAN exposure (RR=0.91, 95% CI: 0.78-1.07). The summary RR for breast cancer is 1.00 (95% CI: 0.995-1.01) for an increment of 1 h of sleep per night. No significant dose-response relationship between sleep duration and breast cancer was found either for the linearity test (Ptrend=0.725) or for the nonlinearity (Ptrend=0.091) test. An increasein of 15 ng/mg creatinine in urinary 6-sulphatoxymelatonin is associated with a 14% reduced risk for breast cancer (RR=0.86, 95% CI: 0.78-0.95), with a linear dose-response trend (Ptrend=0.003). There was no evidence of substantial heterogeneity or publication bias in the analysis. Our study adds to the evidence of LAN breast cancer theory. Further research in this area is warranted.