Camellia sinensis tea consumption and effect on disease progression and remission rates in cancer patients on standard therapy. A systematic review and meta-analysis

Abstract

Background: Tea is an ancient and beloved beverage consumed worldwide. Camellia sinensis is an evergreen shrub used to make green, white, oolong and black tea. The leaves are known to contain significant amounts of polyphenols, a type of protective antioxidant. These polyphenols are linked to several health advantages, most notably as supplementary therapy for the treatment of cancer. Previous clinical research indicated that tea extracts may have cancer-preventing properties. However, its effectiveness remains uncertain. Search methods: A systematic review of clinical research on the effectiveness of consuming Camellia sinensis teas by patients diagnosed with various malignancies was conducted. This project comprehensively searched eligible studies from January 1, 1980, up to July 1, 2024, in all databases (Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE, MEDLINE, PubMed Central® (PMC), Scopus, and reference lists of previous reviews and included studies).Studies were searched and included in accordance with the PICOS criteria, as determined by the PRISMA standards, considering the inclusion and exclusion criteria. JBI SUMARI was utilized to conduct the risk of bias assessment and pool the data to carry out a meta-analysis. Findings were presented on an Excel spreadsheet, and statistics were summarized using a forest plot. Main results: 100 studies were included in this systematic review and meta-analysis. The systematic review revealed that green tea outperformed all other Camellia sinensis teas since the highest and lowest intakes of green tea (> 2 cups/day) were associated with a lower overall cancer incidence (summary RR 0.83, 95% CI = 0.65,1.07). As a result, a meta- analysis was carried out on similar studies of green tea yielding similar outcomes.14 meta- analyses were conducted on green tea and standard anti – cancer treatment versus standard anti – cancer treatment alone, including tests for cancer prevention, cancer risk reduction, and adverse events. All 14 effect sizes were statistically insignificant at p > 0.001 using random-effects model demonstrating an overall high methodological quality based on the JBI 'Risk of bias' assessment tool with no evidence of between-study heterogeneity (I2 < 50). Conclusion: In addition to being safe and well-tolerated, green tea may have beneficial effects on cancer risk reduction. To obtain a definitive conclusion and identify the mechanisms behind this association, future research is necessary. Larger, longer-term prospective cohort and clinical studies on oolong, white, and black tea are also warranted.