Being circumcised may reduce the risk of HIV contamination in heterosexual men by 53%, according to a new study conducted in Africa . The findings were so significant that the US National Institute for Health decided it would be unethical to continue and stopped the trial early. 

During the study, published in the February edition of the Lancet, 4996 men in Uganda and 2748 men in Kenya who were HIV-negative, uncircumcised and aged 18 to 26 were examined for two years.  Most of the men belonged to an ethnic group that does not traditionally practice circumcision. 

According to statistics, 26% of uncircumcised men in Kenya will be infected with HIV by the age of 25. 

The researchers assigned half of the men to voluntary circumcision, and the other half remained uncircumcised during the study. 

All of the participants received free HIV testing and counselling, medical care, tests and treatment for sexually transmitted infections, condoms and behavioural risk counselling during periodic assessments throughout the study. 

Forty-seven of the 1,391 uncircumcised men contracted HIV during the two-year study, compared with 22 of the 1,393 circumcised men. 

There are several reasons why circumcision may protect against HIV infection. Specific cells in the foreskin may be potential targets for HIV infection and also the skin under the foreskin becomes less sensitive and is less likely to bleed reducing risk of infection following circumcision.

 Furthermore, circumcision was associated with reduced risk of urinary tract infections, genital ulcer diseases, and a possible prevention of transmission of human papillomavirus (HPV) - a major risk factor for cervical cancer.  

A downside to this approach might be that circumcised men may feel like they are protected from HIV and may be therefore more likely to engage in risky behavior. 

Still, researchers are hopeful that combining male circumcision with prevention strategies known to reduce HIV transmission -eg, use of barrier methods- would further reduce new infections.