Does drinking black tea increase prostate cancer risk?

Question

A Scottish study in 2012 claimed that heavy black tea drinkers are at higher risk for prostate cancer.

A new study from Scotland has found that men who are heavy tea drinkers may be at higher risk for prostate cancer. However, the researchers point out their study was not designed to find causes, so all they can say is that heavy tea drinking is linked to a higher risk for prostate cancer and not necessarily the cause of it.

Study leader Dr Kashif Shafique of the Institute of Health & Wellbeing at the University of Glasgow, told the media:

"We don't know whether tea itself is a risk factor or if tea drinkers are generally healthier and live to an older age when prostate cancer is more common anyway."

"Most previous research has shown either no relationship with prostate cancer for black tea or some preventive effect of green tea," said Shafique.

But contradictory opinions can be found too.

Men: Drink Black Tea to Reduce Prostate Cancer Risk by 1/3

[...]

a new study out of the Netherlands indicates something as simple as drinking tea could help reduce prostate cancer risk by 1/3.

Researchers found that drinking five or more cups of tea each day could reduce prostate cancer risk by one-third. The study concluded: “In conclusion, dietary flavonoid intake and black tea consumption were associated with a decreased risk of advanced stage prostate cancer.”

Is it true that drinking black tea has an effect on prostate cancer risk?

Answer 1

Per a exploratory meta-analysis of observational studies in 2011 by Zheng J et.al., no association was found between consumption of black tea and risk of prostate cancer. The results of the study were,

For black tea, no statistically significant association was observed for the highest vs. non/lowest black tea consumption.

However per another study by Julia A Montague et.al. in 2012, 'black tea intake may increase prostate cancer risk'.

We report a positive association between black tea intake and prostate cancer risk among a prospective cohort of Chinese men in Singapore. Although our findings support an adverse effect of black tea intake on prostate cancer risk, there is no evident biologic mechanism that can explain the association. Our results need to be confirmed in additional, large prospective studies, and through laboratory data on the biologic plausibility of our finding that black tea is a risk factor for prostate cancer, prior to translating these results into primary prevention strategies.

Regarding prostate cancer and dietary supplements, the National Cancer Institute states,

The 2011 meta-analysis examined the consumption of green and black tea and prostate cancer risk. For black tea, no association was found between black tea consumption and prostate cancer risk.

In a 2015 randomized clinical trial of brewed green and black tea in men with prostate cancer prior to prostatectomy to determine the effect of green tea and black tea consumption on biomarkers related to prostate cancer development and progression by Henning SM, the results and conclusions were

RESULTS: Evidence of a systemic antioxidant effect was observed (reduced urinary 8OHdG) only with GT consumption (P = 0.03). GT, but not BT or water, also led to a small but statistically significant decrease in serum prostate-specific antigen (PSA) levels (P = 0.04).

CONCLUSION: Given the GT-induced changes in NFκB and systemic oxidation, and uptake of GT polyphenols in prostate tissue, future longer-term studies are warranted to further examine the role of GT for prostate cancer prevention and treatment, and possibly for other prostate conditions such as prostatitis.