Tea drinking and risk for prostate cancer (in Scotland if nowhere else)

Back in the dim and distant past (i.e., the 1960s and 1970s), relatively high levels of tea consumption were common in most of the United Kingdom, and coffee was an uncommon substitute. This is certainly not so true today. However, …
a study published recently in Nutrition and Cancer (by Shafique et al.) has been widely publicized in the British media because it found an association between high levels of tea consumption (up to 12 cups of tea per day) and risk for prostate cancer up to 37 years later among a cohort of > 6,000 men in Scotland.

Our friends at The Daily Mail (as usual) were prominent among those who promptly over-reacted to the data in the study results (“Men who drink lots of tea are far more likely to develop prostate cancer, researchers have warned” stated The Daily Mail, in a gross exaggeration of the data.)

Now let’s be clear to distinguish between the quality of the research and the quality of the media reporting.

This study has problems. It was never designed as a study to investigate the impact of tea drinking on risk for prostate cancer diagnosis (let alone prostate cancer death). It is severely flawed by the fact that the amounts of tea consumed by the participants (and indeed all their other activities) were collected just once — at the beginning of the study — back in the recruitment period between 1970 and 1973. It therefore takes no account of the changes in behavior of the study participants between recruitment and the end of the study in 2007. And that’s just one of the many technical problems with this study.

All that the authors state in the study is that men who drank > 7 cups a day in 1970-73 were 50 percent more likely to be diagnosed with prostate cancer over a median follow-up of 28 years than those who drank 0-3 cups a day. To be specific, 6.4 percent of those who drank the most tea developed prostate cancer during the study period, compared with 4.6 percent of those who drank the least, so the absolute hazard ratio of heavy tea drinking on the probability of a prostate cancer diagnosis was very small indeed (even if it was statistically significant). Furthermore, they found no association whatsoever between tea intake and the incidence of low- (Gleason score < 7) or high-grade (Gleason score 8–10) prostate cancer.

For those who are interested in a detailed analysis of this study, we recommend this analysis on the web site of the UK’s National Health Service, which gives a thoughful (if slightly tongue in cheek) assessment of the study and the related media coverage.

What’s The “New” Prostate Cancer InfoLink’s take on all of this? Frankly, this study is of dubious merit at best, and the media coverage (unsurprisingly) has been way out of proportion to the actual data. We doubt if there is a significant percentage of males remaining in the Western world who still drink anything close to 12 cups of tea a day anyway.

3 Responses

  1. Sounds like the PG Tips chimps were included in the sample!

  2. The problem of tea is its origin: An analysis of tea leaves from China showed the presence of 29 pesticides! The Chinese use about 600 different pesticides, but do look for some 30 in the analyses. Chinese standards are not the same as European standards. I do not know U.S. standards. Under these conditions, the benefit is far to be certain …


  3. Jean:

    The tea being drunk by the vast majority of people in Scotland and England in the study period would not have been Chinese forms of tea (commonly “green” tea). It would have been standard forms of “black” tea grown most commonly in countries like India and Kenya. The widespread use of “green” tea in the Western world is really a very recent phenomenon.

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