Professional soccer players are at heightened risk of developing a brain disease that can cause dementia and is usually found in boxers and American football players, according to a new study.

The findings, published in the journal Acta Neuropathologica, looked at 14 retired soccer players with dementia who had started heading the ball in childhood or their early teens.

Post-mortem examinations carried out on six of the players found that four showed signs of chronic traumatic encephalopathy (CTE), far in excess of the average rate for the general population.

"The findings show a potential link between playing football and CTE," the study's lead author, Helen Ling from University College London's Institute of Neurology, told AFP.

"There's now a pressing need to identify the risk involved. Large-scale study is needed and cooperation from professional bodies such as the English Football Association and world governing body FIFA will be required."

It is the first time CTE has been confirmed in a study involving a group of former soccer players.

The unnamed players were 13 ex-pros and one "committed amateur" who played regularly for an average of 26 years.

They were all referred to a psychiatry service in Swansea, Wales between 1980 and 2010.

The earliest signs of dementia started when they were in their mid-60s - compared to an average of the mid-70s for the general population - and 12 of the 14 died with advanced dementia.

Permission from next of kin for post mortems to be carried out was granted for only six of them.

The players whose brain autopsies showed signs of CTE also had Alzheimer's, though Ling said the relationship between the two diseases remains unclear.

"They're two potential brain disorders that can cause dementia," she told media in London.

"It's most likely that a combination of these pathologies has contributed to dementia in these retired footballers.

"The most pressing research question is therefore to find out if dementia is more common in footballers than in the normal population."

The post-mortems were carried out by researchers from University College London and Britain's National Hospital for Neurology and Neurosurgery.

The study did not show whether the damage inflicted on their brains had been caused by heading the ball, aerial collisions with other players or something else.

Unlike boxers and American football players, who regularly receive major blows to the head, soccer players are unlikely to experience significant neurological symptoms or losses of consciousness.

Instead, they are subjected to what the researchers termed "repetitive, sub-concussive head impacts".

Diagnosis problem

CTE can only be diagnosed posthumously and a very small number of former players are known to have had the disease.

They include ex-Brazil captain Hilderaldo Bellini and former West Bromwich Albion striker Jeff Astle, who died in 2002 aged 59.

Astle was originally diagnosed with early-onset Alzheimer's, but a re-examination of his brain revealed he died from CTE that a doctor said was brought on by repeated headers.

A semi-pro American soccer player named Patrick Grange died of CTE in 2012, which researchers say is a sign the condition cannot just be linked to the repeated heading of heavy leather balls.

Several high-profile former players have contracted Alzheimer's, including three of England's 1966 World Cup-winning team: Martin Peters, Nobby Stiles and Ray Wilson.

England's FA said it supports research into degenerative brain diseases in former players and has called on FIFA to investigate.

FIFA's former chief medical officer Jim Dvorak, has said there is "very little evidence" linking players' brain trauma and dementia.

In the United States, children under 11 have been banned from heading in response to a lawsuit brought by parents and players concerned about concussion.

The British researchers said the risk of recreational players developing brain problems from heading is "extremely low".

A new British study suggests heading increases the risk of brain damage in professional soccer players. Reuters