The new German video review ran into trouble on its first serious test but despite the embarrasment officials insist it did not decide the Bayern Munich win over Borussia Dortmund in Saturday's Super Cup (AFP Photo/Odd Andersen)

Zurich (AFP) - FIFA insisted Thursday there is no conclusive proof that heading a ball causes an increased risk of brain disease, after the release of a study on footballers who died from dementia.

"To our very best knowledge, there is currently no true evidence of the negative effect of heading or other sub-concussive blows," football's world body said in response to calls by British neurological experts for greater research.

"Results from studies on active and former professional football players in relation to brain function are inconclusive," a spokesman said in a statement.

The spokesman acknowledged that professional players are "more exposed to all football activities including heading from early childhood than recreational players."

But FIFA said: "Fortunately, football (soccer) does not belong to the high-risk sports for brain and head injuries."

A British study said professional footballers are at heightened risk of developing a brain disease that can cause dementia and is usually found in boxers and American football players.

The study, published in the Acta Neuropathologica journal, looked at 14 retired footballers with dementia who started playing football and heading the ball in childhood or early teens.

Post-mortem exams on six of the players found that four showed signs of chronic traumatic encephalopathy (CTE), far in excess of the average rate of 12 percent found in the general population.

It is the first time CTE has been confirmed in a study involving ex-football players.

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

"Large-scale study is needed and cooperation from professional bodies such as the FA (Football Association) and FIFA will be required," she said.

All of the ex-players involved had been referred to a psychiatry service in Swansea, Wales between 1980 and 2010. Twelve of the 14 died with advanced dementia.

FIFA said that it has been "actively following the issue of head and brain injuries" for more than 15 years including publishing scientific studies with international sports federations and research groups.

It said rule changes toughening sanctions for elbow to the head blows and introducing a head injury protocol in 2014 had cut head injury numbers.

FIFA quoted one international study on children aged seven to 12 years which indicated there was "one concussion with ball contact every 200,000 playing hours."

"FIFA will continue to monitor the situation of head injuries, maintaining constant contact with current and on-going studies regarding long-term neurocognitive changes, both in male and female football players," the spokesman said declaring the health of players to be "a top priority in developing the game."