The anticancer properties of tea polyphenols have shown effectiveness in animal studies but not human

Tea, especially green tea, has attracted significant attention for its potential anticancer properties. Research suggests that polyphenolic compounds in tea, particularly epigallocatechin gallate (EGCG), may inhibit cancer development through various mechanisms. In animal experiments, tea extracts and tea polyphenols have been proven to suppress tumor formation and progression in multiple organs. These studies provide preliminary evidence for the anticancer potential of tea. Below are some key findings from research studies.

The summary relative risk for the highest consumption (≥5 cups/day) of green tea on liver cancer incidence compared with nondrinkers was 0.62 (95% confidence interval: 0.49–0.79). We also found a trend that the incidence of liver cancer was reduced with the increasing years of green tea intake (significance at >20 yr). A significant dose–response association was found between green tea drinking and liver cancer risk. The downward trend was most obvious when the consumption of green tea increased up to about 4 cups/day. The results showed that the increasing green tea intake may have a preventive effect against liver cancer.

recently examined the effect of PPE on the development of aberrant crypt foci (ACF) and adenocarcinoma in the colons of rats treated with azoxymethane. The treatment of rats with PPE (0.24% in the diet) for 8 weeks decreased the total number of ACF per rat by 36.9%. In ACF with high-grade dysplasia the inhibitory activity of PPE was associated with decreased levels of nuclear β-catenin and cyclin D1, and increased retinoid X receptor-α staining41. Treatment with 0.24% PPE for 34 weeks decreased the incidence of adenocarcinoma by 60% and the multiplicity of adenocarcinoma and adenoma by 80% and 45%, respectively (C.S.Y. et. al, unpublished observations). In a model using a food carcinogen, PhIP (2-amino-l-methyl-6-phenylim-idazo[4,5-6]pyridine), to induce colon carcinogenesis in rats, treatment with EGCG during the post-initiation stage for 15 weeks reduced ACF formation by 71% compared with water-treated controls. Conversely, in rats given PhIP and a high-fat diet, subsequent administration of tea (2%) or caffeine (0.065%) in drinking water, in the post-initiation stage, significantly increased colon tumour incidence. This suggests that caffeine can promote colon tumorigenesis under these experimental conditions.

The analysis results indicate that tea consumption is associated with a 22% reduction in the risk of colorectal cancer compared to non-tea drinkers or those with low tea intake (OR = 0.78, 95% CI = 0.68–0.90). The narrow confidence interval suggests a high degree of precision in this study's findings. Although epidemiological studies on the cancer-preventive effects of tea have shown inconsistent conclusions, meta-analyses have suggested that tea consumption may have protective effects against other malignancies such as ovarian cancer, esophageal cancer, and breast cancer. Many laboratory studies, both domestic and international, have also provided supporting evidence. Animal studies using mice as models have shown that treatment with tea polyphenols reduces the number of abnormal crypt foci and the average number of tumors per mouse compared to the control group.

Compared to non-tea drinkers, regular tea consumption is associated with a 29% reduction in the risk of hypopharyngeal cancer. Drinking 0–1 cups of tea per day is associated with a 9% reduction in the risk of head and neck cancer and a 27% reduction in the risk of hypopharyngeal cancer.

Studies have used a fixed-effect model to calculate the overall relative risk (RR) and conducted heterogeneity tests on combined studies. Two studies on breast cancer recurrence and seven studies on breast cancer incidence were identified.

Higher green tea consumption (more than three cups per day) was negatively associated with breast cancer recurrence (pooled RR = 0.73, 95% CI: 0.56–0.96).

Although animal studies have shown promising results, the anticancer effects of tea have not been consistently confirmed in human studies. Some epidemiological studies suggest that regular tea consumption may be linked to a reduced risk of certain cancers, but the results remain inconsistent. Therefore, more large-scale, long-term human studies are needed to determine the exact role of tea in cancer prevention.

Fighting cancer remains one of the greatest challenges in medicine, and the precise mechanisms by which tea compounds affect cancer development are not yet fully understood. Scientists believe that tea polyphenols have strong antioxidant properties, which help neutralize free radicals, reduce DNA damage, and minimize oxidative stress. Additionally, polyphenols promote the metabolism and elimination of carcinogens and regulate cell signaling and metabolic pathways, leading to cell behavior changes, including apoptosis (programmed cell death), cell proliferation, and angiogenesis. Furthermore, tea polysaccharides may regulate cell cycle-related proteins, induce cell cycle arrest, and inhibit tumor formation.

Cancer research is ongoing, and we look forward to future breakthroughs in AI-driven studies, which may help clarify and validate the potential health benefits of tea in cancer prevention and treatment.