In an attempt to explain why the professionals were less likely to face severe mental health disorders, the study said: “One possible confounding factor contributing to our observations is that individuals pursuing a career as an elite athlete may have inherent health differences from the general population, the so called ‘healthy worker’ effect.
“In other words, conceptually, mental health issues might at some level serve as an impediment to pursuit of a career as an elite soccer player.”
The link between the impact of heading footballs and concussion and an increased risk of developing neurodegenerative disease has not been established, but Professor Stewart said last year: “What we have is more than enough evidence, adding up over the decades and right up to the FIELD study at the end of last year, which says there’s a strong association between contact sports and development of dementia.
“And when we look at what is the common factor, exposure to head injury and head impact is the one thing that stands through.”
The study compared deaths of 7,676 ex-players to 23,000 from the general population while the sample was taken from men who played professional football in Scotland, and were born between 1900 and 1976.
They were five times more likely to die of Alzheimer’s, four times more likely to die of motor neurone disease and twice as likely to die of Parkinson’s.
The English, Scottish and Northern Irish football associations banned young children from heading a football during training following the report.
Children under the age of 12 are not allowed to head the ball, and there are restrictions in place around heading during training sessions for those aged between 12 and 17.