The findings, from a study of 14 former players, suggest a possible link between playing football and developing such conditions later in life, researchers said.
The results provide a platform for a “pressing research question” on whether dementia is more common in footballers than the general population, Dr Helen Ling, lead author of the UCL Queen Square Brain Bank study said.
Chronic traumatic encephalopathy (CTE) can cause dementia and, like Alzheimer’s disease, is characterised by a build-up of abnormal tau protein in the brain.
The rate of CTE detected in the brains of the players was greater than the 12 per cent average found in a previous study which looked at brains from the general population.
The results show more research is urgently needed to assess risks faced by players and allow measures to be put in place to protect footballers from long-term damage, Professor Huw Morris of UCL Institute of Neurology said.
“We do not yet know exactly what causes CTE in footballers or how significant the risk is,” said Prof Morris.
“Major head injuries in football are more commonly caused by player collisions rather than heading the ball.
“The average footballer heads the ball thousands of times throughout their career, but this seldom causes noticeable neurological symptoms.”
The players involved in the study, 12 of whom eventually died of advanced dementia, all began playing football and heading the ball when they were children or teenagers and continued for an average of 26 years.
They were all referred to the Old Age Psychiatry Service in Swansea, Wales between 1980 and 2010.
Consultant psychiatrist Dr Don Williams, who ran the study said he was motivated to do so after being approached by a man whose footballer father had been diagnosed with dementia, and who wanted to know if headers could be the cause.