Green tea helps prevent certain cancers, cardiometabolic diseases

Drinking green tea provides certain health benefits particularly for cardiovascular disease (CVD) and some cancer sites, according to a study.

“The evidence on green tea consumption and health outcomes presented in this review suggests green tea may be favourable for cardiovascular disease, particularly stroke, and certain cancers such as endometrial, oesophageal, lung, non-Hodgkins lymphoma, oral, and ovarian cancer,” the authors said.

The databases of PubMed, Web of Science, and Cochrane were searched for studies on green tea between 1980 and 2020 with no language restrictions. The authors identified 551 papers and hand-searched references to include additional possible relevant studies (n=11). Only 107 abstracts remained after excluding duplicates and those not related to the topic.

Of the remaining papers, 82 were found eligible for the meta-analysis. The authors also consulted the World Cancer Research Fund CUP and IARC Monographs for available expert evidence on cancer-related outcomes as well as major original recently published peer-reviewed papers.

An inverse association was observed between green tea consumption and certain individual cancer sites, namely endometrial, lung, oral, and ovarian cancer and non-Hodgkin’s lymphoma. There were mixed findings for breast, oesophageal, gastric, and liver cancers and a null association for colorectal, pancreatic, and prostate cancers. [Eur J Clin Nutr 2021;75:865-876]

Green tea consumption also did not show any cancer-related adverse effects. However, drinking hot tea were found to potentially elevate the risk of oesophageal cancer. Hepatoxicity concerns were also raised due to high doses of green tea.

An inverse association was also observed between green tea consumption and CVD-related health outcomes, but the evidence for diabetes-related health outcomes was lacking. Moreover, green tea inversely correlated with body mass index (BMI)-related and blood pressure (BP) outcomes.

The beneficial effect of green tea on cardiovascular health could be explained by polyphenols exerting antioxidant effects on the cardiovascular system, high concentrations of epigallocatechin gallate, regulation of intermediary outcomes such as BP, body fat, and lipids, and improved glycaemic control. [Am Fam Physician 2009;79:591-594; Obesity 2007;15:1473-1483; Am J Clin Nutr 2011;94:601-610; Am J Clin Nutr 2013;97:750-762]

In addition, caffeine could contribute to regulating blood vessel homeostasis. [Pharmacol Rev 1997;49:1-51; Arterioscler Thromb Vasc Biol 2008;28:1967-1974]

“The findings of this review suggest a weak association between green tea and BMI and weight loss, though further studies are needed to confirm green tea’s potential therapeutic use for obesity,” the authors said. [Obes Rev 2016;17:1316-1328]

On the other hand, fewer studies examined the association of green tea with other health outcomes, including respiratory disease, dental health, injuries, and cognitive outcomes.

“More evidence is needed to assess the impact of green tea on breast, gastric, and liver cancer risk,” the authors said. “Additional studies could also help clarify the suggested null association with certain cancer sites: colorectal, pancreatic, and prostate cancer.”

Of note, one paper reported possible minor adverse effects on health from green tea consumption, but this finding must be interpreted with caution within the study context and possible finer dose-response implications, according to the authors.

“More studies investigating a possible association between green tea consumption and other health outcomes such as cognition, injuries, respiratory disease would be informative to more completely assess the impact of green tea on human health,” they added.