Abstract
Current experimental and epidemiological studies provide inconsistent evidence toward the association between tea consumption and cancer incidence. We investigated whether tea consumption was associated with the incidence of all cancers and six leading types of cancer (lung cancer, stomach cancer, colorectal cancer, liver cancer, female breast cancer and cervix uteri cancer) among 455,981 participants aged 30–79 years in the prospective cohort China Kadoorie Biobank. Tea consumption was assessed at baseline (2004–2008) with an interviewer-administered questionnaire. Cancer cases were identified by linkage to the national health insurance system. Cox proportional hazard regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). In the present population, daily tea consumers were more likely to be current smokers and daily alcohol consumers. 22,652 incident cancers occurred during 10.1 years follow-up (5.04 cases/1000 person-years). When we restricted analyses to non-smokers and non-excessive alcohol consumers to minimize confounding, tea consumption was not associated with all cancers (daily consumers who added tea leaves > 4.0 g/day vs. less-than-weekly consumers: HR, 1.03; 95%CI, 0.93–1.13), lung cancer (HR, 1.08; CI, 0.84–1.40), colorectal cancer (HR, 1.08; CI, 0.81–1.45) and liver cancer (HR, 1.08; CI, 0.75–1.55), yet might be associated with increased risk of stomach cancer (HR, 1.46; CI, 1.07–1.99). In both less-than-daily and daily tea consumers, all cancer risk increased with the amount of tobacco smoked or alcohol consumed. Our findings suggest tea consumption may not provide preventive effect against cancer incidence.
Highlights
Tea is a commonly consumed beverage in various populations
We further examined the association between tea consumption and risks of all cancers as well as the other six leading cancers in our population—lung cancer, stomach cancer, colorectal cancer, liver cancer, and female breast cancer and cervix uteri cancer
We examined the association between tobacco smoking and cancer risk, and between alcohol consumption and cancer risk by different status of tea consumption
Summary
In vitro and in vivo experiments have demonstrated that tea polyphenols may prevent the occurrence of cancer. Extended author information available on the last page of the article through antioxidation, growth inhibition and apoptosis induction [1]. The association between tea consumption and cancer risk remains controversial based on evidence from human studies. Case–control studies consist of the majority of evidence supporting the cancer-preventive effects of tea, while they are subject to recall bias and reverse causality as prediagnostic symptoms of cancer may change the drinking habits. Most recent prospective cohort studies have not found associations between tea consumption and cancer incidence [2,3,4,5]. Some studies even suggested elevated risks for stomach cancer and several subtypes of breast cancer among tea consumers, probably because the caffeine in tea could stimulate secretion of gastric acid and increase the level of estrogen and progesterone [6,7,8]
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