Research by the University of Washington in Seattle has shown traumatic brain injury (TBI) increases the risk of Alzheimer’s and other forms of dementia by 24% over a period of 36 years.
The team studied health data of 2.8 million people who were living in Denmark in 1995 and were aged 50 at some point between 1997 and 2013.
They found 132,093 people had a TBI at some point between 1977-2013, and 126,734 were diagnosed with a form of dementia between 1999 and 2013.
Researchers found the “fully adjusted risk of all-cause dementia in people with a history of TBI was higher than in those without a history of TBI, as was the specific risk of Alzheimer’s disease”.
According to the study even a relatively minor knock on the head resulting in concussion can lead to a 17% risk increase.
Lead author Professor Jesse Fann said: “Individuals with a history of traumatic brain injury, including those with less severe injuries, have an increased risk of developing dementia, even decades after the injury.
“However, it’s important to emphasise that although the relative risk of dementia is increased after traumatic brain injury, the absolute risk increase is low. Our findings do not suggest that everyone who suffers a traumatic brain injury will go on to develop dementia in later life.”
The research may lend support to campaigns for better safety in sports including football, boxing and rugby.
West Brom player Jeff Astle died aged 59 of a degenerative brain disease and his daughter Karen Astle has campaigned for more research into the effects of players heading the ball during games.
A coroner ruled the repeated minor traumas from heading the ball ultimately caused Astle’s death.
Chesterfield’s Ernie Moss is still the club’s highest goalscorer, but requires round the clock care as he battles his dementia. His family says it is linked to his playing days.
Previous studies have been conflicting, because of small sample sizes and short follow-up periods.
However researchers in this study took account of other influences on dementia risk, like diabetes, heart disease, depression and substance abuse.
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They identified and cumulative effect, and found dementia risk rises with repeated episodes of brain injury. It was increased nearly three-fold for people who suffered more than four TBIs.
A single TBI increased the risk by more than a third.