Oct. 7 (Bloomberg) -- Circumcision, which can slow the spread of the AIDS virus from women to men during sex, doesn't appear to provide the same protective effect for men having sex with other men, U.S. researchers said today.

While circumcised gay men were 14 percent less likely to be infected with the AIDS virus than uncircumcised men, the difference missed the level needed to show that it wasn't the result of chance, said researchers led by Gregorio Millett, a Centers for Disease Control and Prevention behavioral scientist. The results from an analysis of 15 earlier studies that included 53,567 homosexual men were published in the Journal of the American Medical Association.

Circumcision is the surgical removal of a flap of skin from the tip of a man's penis. Three large African studies have shown that circumcision can lower heterosexual men's risk of infection by the AIDS virus, HIV, by almost two-thirds. Better designed studies might show the procedure helps certain gay men, if they exclusively participate as the insertive partner in anal sex, to avoid HIV, Millett said in a telephone interview.

``These studies weren't designed to answer this question in the first place, and it's possible that they're too varied to show an effect,'' he said yesterday in a telephone interview. ``The idea makes sense, but there just aren't enough data out there right now to show whether there's a benefit.''

Risky Sex Returns

The one situation in which research confirmed the benefit of circumcision for gay men was in the period before 1996, when doctors began using powerful combinations of antiviral drugs that reduce the amount of virus in blood and semen. Before the antiviral drugs were available, many gay men had avoided risky sex practices and under those circumstances, circumcision may have provided protection. With the drugs, some men may have resumed engaging in risky sex without condoms, skewing the results of the study, Millett's team said.

Still, that might provide enough evidence to suggest that some homosexual men -- those who only have insertive sex -- might be counseled about the possible benefits of circumcision, said Daniel Halperin, a Harvard School of Public Health researcher. Other studies recently conducted in such men in Australia and Peru have shown a strong protective effect, he said.

``For them, it might have a pretty big impact,'' Halperin said yesterday in a telephone interview. ``It's biologically plausible, and I don't know if we should wait years for a large study to prove it.''

Infections Spread Worldwide

About half of the 1.1 million Americans infected with HIV are homosexual men, according to the Atlanta-based CDC. The proportion of gay men who participate only as the insertive partner in anal sex is difficult to determine, and is probably small, Halperin said.

Experimental vaccines and protective gels have failed to prevent the spread of HIV since it was discovered about a quarter century ago, and about 33 million people are infected worldwide today with the lethal virus. The World Health Organization, the Bill & Melinda Gates Foundation and the U.S. are supporting circumcision clinics in poor African countries where the virus is spreading widely.

Circumcision, while somewhat expensive, is a one-time procedure that can reduce the risk of acquiring HIV for life. Researchers believe it does so by removing the foreskin, a portion of the penis that's most vulnerable to sexually transmitted infections, including HIV.

If that approach is effective in men who only have intercourse with women, it would probably also function in men who engage as the insertive partner in anal sex. However, the procedure offers no protection to men who are receptive during anal sex.

``Even if we find that insertive men are protected, that might be such a small proportion that we wouldn't get the effect on the overall population that we'd like,'' Millett said. ``As it stands now, circumcision is unlikely to have the same kind of benefit here that it's projected to have in Africa.''

To contact the reporter on this story: John Lauerman in Boston at jlauerman@bloomberg.net.

Last Updated: October 7, 2008 16:00 EDT