Previous studies investigating the correlation between tea intake and incidence of gynaecologic cancers have produced conflicting results.
To evaluate this association, a meta-analysis based on 19 cohort studies, which involved 2,020,980 subjects and 12,155 gynaecological tumour cases, was conducted by Chinese researchers.
According to the findings, the pooled relative risk (RR) of tea intake for ovarian cancer, endometrial cancer and cervical cancer were 0.94, 1.02 and 1.06 respectively.
Tea types were then separated for subgroup analyses, where it was found that non-herbal tea had significant preventive impact on ovarian cancer (pooled RR of 0.67), especially for black tea (pooled RR of 0.64).
Non-herbal tea is mainly divided into green, black, white, oolong, yellow, and Pu-erh.
Furthermore, a nonlinear dose-response analysis showed a decreasing trend of ovarian cancer risk when the tea consumption was 1.40 to 3.12 cups per day.
However, the role of tea in preventing ovarian cancer was not significant at higher consumption levels, which may be due to less data being available for review or that excessive tea consumption is less effective against tumours, said the authors.
“Our findings showed that ovarian cancer, but not other gynaecologic cancers, could possibly be prevented by drinking non-herbal tea. In addition, the preventive impact of green tea on gynaecologic cancer seemed to be relatively weak and needs further cohort studies to validate it,” the authors added.
Anti-cancer effects of tea
In the past, gynaecological tumours were mostly associated with oestrogen exposure and metabolism. Over the years, numerous epidemiological studies have indicated that the risk and mortality of these cancers could be affected by diet.
A popular and widely consumed beverage, teas and their components have been extensively studied for their impact on human health.
In particular, the health benefits of black tea, such as anti-inflammatory properties, are mainly attributed to its active ingredients, including flavonoids and phenolic acids.
“There is a lot of evidence that black tea can inhibit the occurrence and development of tumours by regulating oxidative damage, endogenous antioxidants, mutagenic pathways, and transcription of the antioxidant gene pool.
“Based on our findings, the anti-cancer effect of tea seems to be more focused on ovarian cancer, where it may function to induce apoptosis (a form of programmed cell death) and anti-angiogenesis (a treatment that prevents the growth of cancer by blocking new blood vessels from forming), or as adjuvant therapy,” the authors explained.
The meta-analysis also underlined the divergence in mechanisms behind the onset and progress of different gynaecologic cancers. This signals a need for “more randomised controlled trials and large cohort studies including more geographical areas and tea types” to reach definitive conclusions.
It should be noted that there are several limitations to the study, including the lack of data on other cancer risk factors such as family history and dietary intake. Also, the histological types of gynaecological tumours were not classified. This is important because tumours such as ovarian cancer may have heterogeneity with different sensitivities and responsiveness to tea components.
“Nevertheless, our study suggests that the positive effects of black tea on the intervention of ovarian tumours could be further explored,” the authors reiterated.
“Association between Different Types of Tea Consumption and Risk of Gynecologic Cancer: A Meta-Analysis of Cohort Studies”
Authors: Fang Zheng, et al