Boys who are circumcised before the age of five are more likely to develop autism, a study has suggested.
Autism is a disability that affects people's communication and behaviour and, according to the paper published in the Journal of the Royal Society of Medicine in January, circumcised boys are more likely "than intact boys" to develop ASD (Autism Spectrum Disorder).
Researchers at Statens Serum Institut, Copenhagen, consulted the national registers to analyse information of 342,877 boys born in Denmark between 1994 and 2003.
"With a total of 4,986 ASD cases, our study showed that regardless of cultural background circumcised boys were more likely than intact boys to develop ASD before age 10 years," the paper said.
The study concluded that circumcision increased the risk of developing ASD by 46%.
Researchers explained that the link between circumcision and autism could be caused by the pain felt during the procedure.
According to some, painful experiences in babies "have been shown in animal and human studies to be associated with long-term alterations in pain perception, a characteristic often encountered among children with ASD."
Others, however, have criticised the report linking circumcision to autism.
Speaking to the Huffington Post, Dr Douglas S Diekema, a pediatrician at the University of Washington in Seattle, warned that people should be careful when drawing conclusions after reading the report, which "raises questions for further study, but does not provide answers. Correlation does not imply or prove causation."
Diekema also explained that if there was a link between circumcision and autism, then the rate of the latter would have fallen in recent decades given that less boys are circumcised now - but in fact the opposite is true.
Dr Howard Cohen, a Mohel (Jewish person trained to carry out circumcision) for the London and South East UK Jewish community, wrote in the Jewish News Online: "The wrong type of study was done to explore whether a causative link exists.
"Observational studies can suggest associations but cannot explain the mechanisms of diseases. The authors seemingly failed to grasp both what autism is or what happens at a circumcision."
The latest research has further ignited the long debate on circumcision.
Supporters of this practice argue that circumcision helps reduce risks of infection, some cancers and also the transmission of STDs (sexually transmitted diseases).
Side-effects of circumcision can include pain, bruising and swelling of the skin around the penis, formation of abnormal scar tissue and damage to the urethra. Opponents argue that this practice can also cause negative effects on sexual health and emotional, sexual and social negative side effects that are visible only after childhood.
Last April, a joint US and Australia study claimed that the benefits of circumcision exceed the risks "a hundreds times over" and that the practice has no adverse effect on sexual function, sensitivity or pleasure.
In May 2014, however, a study from the American Academy of Pediatrics said that risk of circumcision side effects are 20 times greater if boys are subjected to this practice after the first year of birth.
Circumcision is very controversial in some countries, which have banned it. A report published by the European Council in 2013 called the practice a human rights violation.
In 2012, Germany criminalised circumcision if it is carried out for religious purposes.
Medical associations in Sweden and Denmark urged for non-medical circumcision of boys to be banned and last October a survey revealed that almost three quarters of Danes want the practice to be abolished.