The study – the largest of its kind - also found having just one moderate-to-severe concussion, or traumatic brain injury (TBI), can have a long-term impact on brain function, including memory.
Led by teams at the University of Oxford and the University of Exeter, the research included data from more than 15,000 participants of the online PROTECT study, who were aged between 50 and 90 and based in the UK. They reported the severity and frequency of concussions they had experienced throughout their lives, and completed annual, computerised tests for brain function.
Published in the Journal of Neurotrauma, the paper found that people who reported three or more concussions had significantly worse cognitive function, which got successively worse with each subsequent concussion after that. Attention and completion of complex tasks were particularly affected.
Researchers say people who have had concussions should be warned of the dangers of continuing high-risk sport or work.