Research published today by the Journal of the Royal Society of Medicine suggests that circumcised boys are more likely than intact boys to develop autism spectrum disorder (ASD) before the age of 10. Risk is particularly high for infantile autism before the age of five. The research was carried out in Denmark among a cohort of all children born between 1994 and 2003.

During the study over 340,000 boys were followed up to the age of nine between 1994 and 2013 and almost 5,000 cases of ASD were diagnosed. The study showed that regardless of cultural background circumcised boys may run a greater risk of developing ASD. The researchers also made an unexpected observation of an increased risk of hyperactivity disorder among circumcised boys in non-Muslim families.

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.”

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 researchers say that the pain associated with circumcision in very young babies is likely to be more severe during the operation and post-operatively.

Painful experiences in neonates 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.

“Possible mechanisms linking early life pain and stress to an increased risk of neurodevelopmental, behavioural or psychological problems in later life remain incompletely conceptualised,” said Professor Frisch. “Given the widespread practice of non-therapeutic 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.”