Former professional footballers are three and a half times more likely to die of dementia than people of the same age range in the general population, according to new research.
Experts at Glasgow University have been investigating fears that heading the ball could be linked to brain injuries.
The study began after claims that former West Brom striker Jeff Astle died because of repeated head trauma.
It compared deaths of 7,676 ex-players to 23,000 from the general population.
The sample was taken from men who played professional football in Scotland between 1900 and 1976.
The long-awaited study was commissioned by the Football Association and the Professional Footballers' Association after delays in initial research had angered Astle's family.
It began in January last year and was led by consultant neuropathologist Dr Willie Stewart, who said that "risk ranged from a five-fold increase in Alzheimer's disease, through an approximately four-fold increase in motor neurone disease, to a two-fold Parkinson's disease in former professional footballers compared to population controls".
Although footballers had higher risk of death from neurodegenerative disease, they were less likely to die of other common diseases, such as heart disease and some cancers, including lung cancer.
Dr Stewart said: "This is the largest study to date looking in this detail at the incidence of neurodegenerative disease in any sport, not just professional footballers.
"Our data show that while former footballers had higher dementia rates, they had lower rates of death due to other major diseases.
"As such, while every effort must be made to identify the factors contributing to the increased risk of neurodegenerative disease to allow this risk to be reduced, there are also wider potential health benefits of playing football to be considered."
The link between contact sport participation and neurodegenerative disease has been subject to debate in recent years, but until this study, it was not clear whether there was any evidence of an increase in neurodegenerative disease rate in former footballers.
Former England international Astle developed dementia and died in 2002 at the age of 59. The inquest into his death found heading heavy leather footballs repeatedly had contributed to trauma to his brain.
But research by the FA and the PFA was later dropped because of what were said to be technical flaws.
Astle's family has campaigned for the football authorities to launch a comprehensive research programme.
His daughter Dawn said she was "relieved" the study eventually went ahead, and her father's case was highlighted by former England captain Alan Shearer in a BBC documentary Alan Shearer: Dementia, Football and Me.
Speaking about the findings of the Field (Football's Influence on Lifelong Health and Dementia Risk) research, FA chairman Greg Clarke said: "The whole game must recognise that this is only the start of our understanding and there are many questions that still need to be answered.
"It is important that the global football family now unites to find the answers and provide a greater understanding of this complex issue. The FA is committed to doing all it can to make that happen."
PFA chief executive Gordon Taylor added: "These findings are a matter of considerable importance to our members. We are grateful to Dr Willie Stewart and his team for their work.
"It is now incumbent on football globally to come together to address this issue in a comprehensive and united manner. Research must continue to answer more specific questions about what needs to be done to identify and reduce risk factors.
"Our members wellbeing is of paramount importance to us, and we are committed to representing their voice as this conversation opens up across football's stakeholders."
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