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I've seen numerous claims that circumcision reduces HIV risk, both on TV and online.

Have there been any studies to verify if circumcision does or doesn't reduce HIV risk in a statistically-significant manner?

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    Rather important: compared to what? Uncircumcised but wearing a condom? – Konrad Rudolph Jun 8 '11 at 17:55
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    @Konrad -- The only useful question is without a condom for both :P Clearly once you put a condom on.... – Russell Steen Jun 8 '11 at 17:59
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    @Russell On the one hand, yes. On the other hand, this is a loaded statement (people do use the supposed preventative effect of circumcision to argue against wearing condoms, which is playing with fire). See also Darwy’s answer. – Konrad Rudolph Jun 8 '11 at 18:52
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    @Konrad -- My experience is that people will use just about anything they can get their hands on to argue for not using a condom. By that logic we shouldn't pursue any improvements in non-condom prevention, because people might use it to argue against wearing condoms. – Russell Steen Jun 8 '11 at 19:46
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    As you look through the evidence in the answers below, I suggest it might help to keep in your head the following questions: Are the studies looking at a population of men who have sexual encounters with other men, a population of men who only have sexual encounters with women, or a real world sample including a mix of both? Are they looking at the risk of a woman being infected by a man, a man being infected by a woman, a circumcised man being infected by an HIV positive man, or a man being infected by a circumcised HIV-positive man? This may explain some of the apparent discrepancies. – Oddthinking Jun 9 '11 at 11:22
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I would have to respectfully disagree with Russell's answer and say: No. Circumcision does not reduce HIV risk.

The three controlled intervention trials suffer from some VERY major design flaws, which cast more than a reasonable doubt about the supposed 'benefit' of circumcision in males.

A Cochrane review of circumcision questions the validity of previously performed studies on circumcision for the following reasons:

  • Performance bias
  • Attrition bias
  • Selection bias

They identified 14 cross sectional studies with inconsistent findings - 4 were statistically significant for a benefit to circumcision, 2 were statistically significant for harm from circumcision. They also mentioned study heterogeneity.

They summarize with (bolded emphasis mine):

In assessing the quality of the observational studies we identified 10 potentially important confounders that studies would need to ensure were either balanced between circumcised and uncircumcised groups or, if unbalanced, that were adequately adjusted for (see Box 2).

Many studies either did not measure these variables or, if reported, were either not balanced between groups or not adjusted for.

It is important to note that observational studies, unlike RCTs, can only adjust for known confounders, and only then if they are measured without error. The effect of unknown confounders may well be operating in either direction within and across all of the included studies.

The studies from high-risk groups included in this review do report a powerful protective effect of circumcision, measured by both unadjusted and adjusted odds ratios. More mixed results were reported for the general population. As all the observed results could be explained by likely confounding, RCTs are essential before circumcision is implemented as a public health intervention. Implementation of circumcision will encounter cost, both financial and in terms of potential personal harm; no adverse effects are reported in this review only because none of the observational studies investigated them. Feasibility issues of implementation are beyond the scope of this review but need to be carefully considered.

If those clinical trials in Africa are flawed, how can one justify using them as the basis for a policy?

There is a real risk of risk compensation reducing the 'benefit' of circumcision.

The various pro-circumcision studies all cite the need for 'other' forms of prevention, ie. condoms - which in Africa aren't as available (or used) as they are elsewhere in the world.

Further Reading:

I'll be happy to counter the other sources at a later point, it's 10:30 pm here and I'm knee deep in setting OEL limits.

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    The CDC page cites over a dozen different studies, both lab and clinical trials. You've questioned one set of clinical trials. One set of trials being flawed does not invalidate an entire body of research. – Russell Steen Jun 8 '11 at 18:36
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    I've questioned all 3 clinical trials, as they are all based upon the same sampling bias, selection bias, etc. How a group of researchers can put forth a recommendation for a procedure such as circumcision as a preventative measure for HIV with no long-term follow up period is unforgivable. – Darwy Jun 8 '11 at 18:39
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    Russell, all the proof you've linked relies on those 3 clinical trials as the basis for the conclusion that circumcision reduces HIV risk. It's a circular argument. Let's examine the Uganda clinical trial: "Male circumcision for HIV prevention in men in Rakai, Uganda: a randomised trial" They're not talking about 'risk reduction' they're talking about PREVENTION. There is no strawman there. – Darwy Jun 8 '11 at 18:48
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    @Billare This answer cites a Cochrane study, pretty much the gold standard in clinical research. If this is a “travesty against science”, I don’t know what science is. You say that hate how fashionable it’s become to be anti-circumcision. But that’s completely irrelevant here. These “fanatics” you speak of oppose an unnecessary intrusive surgery in small infants. That’s just like opposing removal of tonsils or the appendix in healthy people. Which, hey, happens to be almost universal: you don’t generally perform surgery on healthy people. – Konrad Rudolph Jun 9 '11 at 9:15
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    @Billare You make many assumptions - first that your opinion of what is 'pleasing to the eye' is shared by everyone. It isn't. Furthermore, the surgical amputation of healthy tissue is by definition, "unnecessary". Also, it was MY statement that "Circumcision does not reduce HIV risk", it wasn't the study conclusion. The studies I linked (including the Cochrane study) were supporting my statement. Finally - your gender bias is showing. – Darwy Jun 11 '11 at 7:53
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My own answer ripped straight from this question:

The CDC concludes that circumcision does reduce risk of disease based on multiple lab studies and controlled intervention trials, in addition to the statistical research that opponents focus on for "refuting" the evidence.

This is a topic where research has been done and confirmed, it boils down to this:

Research indicates reduced HIV risk for circumcised men, both in labs and in the real world (where people don't always wear condoms, for whatever reason).

References:

Basically every significant health organization in the world is behind this, entailing almost 40 different clinical trials since the 1980s and numerous lab trials demonstrating that the uncut penile tissue around an intact foreskin is more receptive to HIV infection.

Also of note, this only speaks to the risk to the male in question. It also may not apply to subsets (for any medical research you will always be able to find some subgroup of the population that has a different outcome)

Thanks to @OddThinking it appears another real world trial has been performed supporting this claim. This study directly provides real evidence against the risk compensation claim.

Three years after the voluntary medical male circumcision (MC) campaign rolled out in the Orange Farm Township in South Africa, the first “real world” results are available showing a marked reduction of HIV acquisition among circumcised adult men with a 55 percent lower HIV prevalence (proportion of HIV-infected people) among circumcised men compared to their uncircumcised counterparts and overall reduction in HIV incidence (the number of new cases) among men 15 to 34 years old of 76 percent.

  • +1, but it would help to explicitly mention HIV. – MrHen Jun 8 '11 at 18:09
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    Just to comment that Borror0 mentioned a link was broken so I've replaced it with a similar report from the same agency (NIH) – Russell Steen Jun 8 '11 at 18:24
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According to the World Health Organization's Male circumcision for HIV prevention:

There is compelling evidence that male circumcision reduces the risk of heterosexually acquired HIV infection in men by approximately 60%. Three randomized controlled trials have shown that male circumcision provided by well trained health professionals in properly equipped settings is safe. WHO/UNAIDS recommendations emphasize that male circumcision should be considered an efficacious intervention for HIV prevention in countries and regions with heterosexual epidemics, high HIV and low male circumcision prevalence.

See also Male circumcision: a globally relevant but under-utilized method for the prevention of HIV and other sexually transmitted infections Annual Review of Medicine 2014; vol. 65 pages 293-306:

Randomized trials have demonstrated that male circumcision (MC) reduces heterosexual acquisition of HIV, herpes simplex virus type 2, human papillomavirus (HPV), and genital ulcer disease among men, and it reduces HPV, genital ulcer disease, bacterial vaginosis, and trichomoniasis among female partners.

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