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Some studies suggest that black tea consumption may be positively associated with development of breast cancer. Here's link to one study result.

Is it a fact or just a hypothesis?

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  • Hmmm. What is the proportion of tea drinkers to coffee drinkers in Sweden? That could play a role in the figures maybe? Welcome to MedicalSciences.SE Commented Jul 30, 2021 at 14:30

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BACKGROUND

There are a very large number of studies of tea consumption and breast cancer. All of these studies are observational epidemiologic studies. The epidemiologic studies assess black tea and green tea. Concern about the possible carcinogenicity of caffeine is long-standing. It was first evaluated as a possible carcinogen by the International Agency for Research on Cancer (IARC) in 1991.

http://www.inchem.org/documents/iarc/vol51/04-caffeine.html

As a beverage containing caffeine, black tea has became an exposure of interest.

There has been a particular interest in green tea and a possible decrease in the risk of cancer, not limited to breast cancer.

The reasons for the hypothesis that green tea might decrease the risk of breast cancer are explained in a 2014 review:

Wu AH, Butler LM. Green tea and breast cancer. Mol Nutr Food Res. 2011;55(6):921-930. doi:10.1002/mnfr.201100006

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4196858/

Thus, these authors explain that:

“Green tea is rich in tea catechins, namely epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin (EC), and epicatechin gallate (ECG), which have many cancer chemo preventive attributes including anti-oxidation, anti-inflammatory, anti-proliferative, and anti-angiogenic [5]. In addition, EGCG has been found to exhibit steroid hormone activities [6–8] and may influence breast cancer risk via hormonal mediated pathways.”

UMBRELLA REVIEW OF TEA AND CANCER

As explained in the WIKIPEDIA, an umbrella review is:

“a review of systematic reviews or meta-analyses.”

https://en.wikipedia.org/wiki/Umbrella_review

An umbrella review published in 2020 looked at tea consumption and the risk of cancer. The review assessed meta-analyses of studies not just of breast cancer but all cancer. In this umbrella review, published meta-analyses of studies of green tea and black tea were identified. The umbrella review was based on a search of the PUBMED and EMBASE databases and was limited to meta-analyses published in English up to April 30, 2019.

Kim TL, Jeong GH, Yang JW, et al. Tea Consumption and Risk of Cancer: An Umbrella Review and Meta-Analysis of Observational Studies. Adv Nutr. 2020;11(6):1437-1452. doi: 10.1093/advances/nmaa077

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7666907/

Table 4 of the published paper presents the findings of the review in a format that is most easily understood. This Table shows summary (meta-analyzed) estimates of the relative risk of breast cancer for high versus low black tea consumption and high versus low green tea consumption for all studies and separately for cohort and case-control studies. The following are these estimates extracted from Table 4.

Breast Cancer Estimated Summary Relative Risk (95% Confidence Interval) High Versus Low Tea Consumption

Black Tea

No. of studies RR (95% CI) Level of Evidence
All 28 RR 0.98 (95% CI 0.92, 1.06) Nonsignificant
15 cohort studies RR 1.04 (95% CI 0.97, 1.12) Nonsignificant
13 case-control studies RR 0.91 (95% CI 0.80, 1.03) Nonsignificant

Green Tea

No. of studies RR (95% CI) Level of Evidence
All 16 RR 0.82 (95% CI 0.71, 0.96) Weak
5 cohort studies RR 0.99 (95% CI 0.83, 1.77) Nonsignificant
11 case-control studies RR 0.75 (95% CI 0.61, 0.92) Suggestive

UMBRELLA REVIEW: AUTHOR CONCLUSIONS ABOUT BLACK TEA AND GREEN TEA

The authors did not state a specific conclusion about the association of black tea with the risk of breast cancer. Based on a comparison of high and low green tea consumption, the authors concluded that the data about green tea and lower breast cancer was “suggestive" but called for more research.

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  • You have missed out in the conclusions that "breast cancer (high compared with low green tea consumption) being classified as suggestive evidence despite showing very large heterogeneity (I2 > 75%) (see Supplemental Table 3). However, several limitations to this study can be considered..." Commented Sep 8, 2021 at 11:51
  • At the end of the conclusions, the paper points out that "The association between tea consumption and the risk of oral cancer was supported by convincing evidence. It is possible that tea consumption can reduce the risk of some other cancers, but further prospective and mechanistic studies are needed before more robust conclusions can be made" Commented Sep 8, 2021 at 11:53
  • @Chris Rogers The authors did conclude that the association between tea consumption and a lower risk of oral cancer was supported by what they considered "convincing evidence." As you point out, the authors also state that it is "possible" that tea consumption can reduce the risk of "some other cancers." But the OP asked about breast cancer and tea consumption and the answer deals only with breast cancer. The answer states that the authors concluded that the data about green tea and breast cancer was "suggestive." I don't see your point. The table edits are nice! Commented Sep 9, 2021 at 14:46
  • The point I was making is that although the authors said the link to breast cancer was "suggestive", they also stated that there were limitations to the study and therefore further studies are needed before robust conclusions can be made. Adding this, in my opinion, would make your answer less suggestive that they were robust conclusions. Especially when they considered evidence based on all 16 green tea studies was weak and all black tea studies had "nonsignificant" evidence. Commented Sep 9, 2021 at 14:58
  • @Chris Rogers Edited to add basis for the authors conclusion and their call for more research. I found their approach to evidence synthesis to be pretty "flaky" but that is an opinion. Commented Sep 9, 2021 at 15:03

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