You can keep drinking the java (maybe)

The conclusion of a meta-analysis of data from 12 prior studies suggests that drinking coffee has no significant impact on risk for prostate cancer. This news will no doubt come as a great relief to the good people at Starbucks!

Park et al. identified 12 epidemiological studies published prior to August 2009 (including eight case-control studies and four cohort studies) that met predefined criteria for analysis of the impact of coffee consumption on risk for prostate cancer. They then carried out a variety of meta-analyses based on the crude and adjusted data in all 12 articles.

Their results showed the following:

  • The overall relative risk (RR) for prostate cancer among men having the highest level of coffee consumption — as compared to men with the lowest level — was 1.16.
  • When studies were grouped by study design and a meta-analysis was carried out by subgroup,
    • There was a significant positive (i.e., harmful) association between coffee consumption and prostate cancer risk in 7/8 case-control studies (RR 1.20).
    • There was no significant association in the four cohort studies (RR 0.97).

The authors conclude that, “Given that a cohort study gives a higher level of evidence than a case-control study, there is no evidence to support a harmful effect of coffee consumption on prostate cancer risk.”

Of course a meta-analysis of 12 sets of data on something like coffee drinking is fraught with complications. Just how much coffee were people drinking? How strong was the coffee? With or without milk and/or sugar? Should these data be compared to data from men drinking no coffee at all? How much variation was there between the 12 case-control and cohort studies? There is a long list of unresolved questions.

The only way one could really get a good answer to the question whether coffee consumption affects risk for prostate cancer would be to collect data with great accuracy from several thousand men over about 20 years, including a group of men who drank no coffee at all. While the current study may give us a general sense that any risk associated with coffee consumption may be relatively small, we really can’t conclude from studies like this that there is no association between drinking coffee and risk for prostate cancer.

The most accurate conclusion from this meta-analysis would be that available data provide no concrete evidence that coffee consumption either raises or lowers risk for prostate cancer. Proving a negative in this type of study is, in fact, near to impossible.

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