But experts have urged caution over the 'extremely speculative findings'

Study looked at 340,000 boys born in Denmark between 1994 and 2003

This may in turn affect how the brain develops and reacts to stress

They suggest the pain caused by circumcision may be partly to blame

Circumcision before the age of five can double a boy's risk of developing autism, controversial research suggests.

Scientists believe the finding may be linked to stress caused by the pain of the procedure.

The study of more than 340,000 boys in Denmark found that circumcision raised the overall chances of an autism spectrum disorder before the age of 10 by 46 per cent.

But if circumcision took place before the age of five it doubled the risk.

Circumcision also appeared to increase the likelihood of boys from non-Muslim families developing hyperactivity disorder.

Regardless of cultural background, circumcised boys may run a greater risk of developing autism and ADHD, a study has claimed

The research, published in the Journal of the Royal Society of Medicine, examined more than 340,000 boys born in Denmark between 1994 and 2003.

At the age of nine, their health was tracked - and almost 5,000 cases of ASD were diagnosed.

Professor Morten Frisch of the Statens Serum Institut, Copenhagen, who led the research, said: 'Our investigation was prompted by the combination of recent animal findings linking a single painful injury to lifelong deficits in stress response...and a study showing a strong, positive correlation between a country's neonatal male circumcision rate and its prevalence of ASD in boys.

He added: 'Today it is considered unacceptable practice to circumcise boys without proper pain relief.

'But none of the most common interventions used to reduce circumcision pain completely eliminates it and some boys will endure strongly painful circumcisions.'

The study goes on to discuss how painful experiences in babies have been shown - both in animal and human studies - to have a long-term effect on pain perception.

This is a characteristic often encountered among children with autism, they add.

BENEFITS OF CIRCUMCISION 'OUTWEIGH THE RISKS': PROCEDURE CUTS THE RISK OF HIV, STDS AND PENILE CANCER, OFFICIAL REPORT DECLARES There is clear scientific evidence that the benefits of circumcision outweigh the risks, a landmark report has declared. A debate has long raged over the ethics of the procedure - and some men believe it has affected their sexual function or satisfaction. But U.S. officials have now said the medical evidence supports having the procedure. The announcement came in new long-awaited draft guidelines released by the Centers for Disease Control and Prevention (CDC). This is the first time the U.S. Government has released such a report on circumcision, where the foreskin around the tip of the penis is cut away. While the guidelines stop short of telling parents to get their newborn sons circumcised, they are very clear on the health advantages. Advertisement

Professor Frisch said: 'Given the widespread practice of circumcision in infancy and childhood around the world, our findings should prompt other researchers to examine the possibility that circumcision trauma in infancy or early childhood might carry an increased risk of serious neurodevelopmental and psychological consequences.

However experts have urged caution over the findings.

Professor Jeremy Turk, Consultant Child & Adolescent Psychiatrist at Southwark Child & Adolescent Mental Health Neurodevelopmental Service, said: 'The findings of this research, while interesting, need to be considered carefully - one cannot draw very strong conclusions from the data.

'This is not a causal study, but instead compares data sets and looks for correlations.

'While this is a valid way of doing a study, it means that we must be careful about any implications.

'For example, many cases of autism are missed until children are older and as there are relatively few cases of autism this could easily skew the data.

'Furthermore, there are many potentially confounding variables which could explain raised ASD rates, which the authors do not explore or account for.

'Finally, I have some issues with the premise in that their speculations regarding early pain as a cause of autism are, to say the least, highly speculative.

And Dr Rosa Hoekstra, lecturer in psychology at the Open University, said: 'I think this is an extremely speculative study.

'The study is purely based on register data and takes a registered autism diagnosis at face value, without considering cultural or social factors affecting the likelihood of an (early) autism diagnosis.

The researchers suggest the pain caused by circumcision may be partly to blame, in turn affecting how the brain develops and reacts to stress

'Even in a high income country like Denmark not all children with autism are detected and given a suitable autism diagnosis at an early age (the age under study in this paper).

She added: 'An entirely different but in my view much more plausible explanation is as follows: Boys with symptoms of autism who undergo circumcision by a medical professional may have their symptoms recognised as autism more often, and at an earlier age, than boys who are not circumcised and who may therefore fly under the radar of medical professionals.

'In other words: the detection rate of autism (rather than the risk of autism per se) may be higher in boys seeing a medical professional for circumcision.

Today it is considered unacceptable practice to circumcise boys without proper pain relief. But none of the most common interventions used to reduce circumcision pain completely eliminates it and some boys will endure strongly painful circumcisions

Professor David Katz, from University College London, who chairs Milah UK, a body that speaks for the Jewish community on issues related to circumcision, said: 'This report is far from convincing: correlation does not equal causation.

'There is a long history of attempts to link autistic spectrum disorders to unrelated practices, such as the measles/mumps/rubella association, which proved to be fraudulent.

He added: 'There is general agreement that in people suffering from an ASD there are abnormalities that can be identified in brain structure and/or function.

'There is a strong genetic component, which may be a factor within the faith communities studied here, and which does not appear to have been explored amongst them.

'Some contemporary research does indicate that factors besides the genetic component are contributing to the increasing occurrence of ASD.

'For example, a variety of environmental toxins have been invoked to explain why these conditions are more prevalent today than they may have been in the past - but again proof of causation is lacking, and these factors are only likely to be relevant in those who are already vulnerable to them.'