"For me, this study clearly highlights that mild injuries are not necessarily mild in terms of their impact on people's lives," Theadom told the Herald. "For nearly half of the sample, even one mild brain injury led to people experiencing multiple long-term difficulties one year later. The findings contradict previous expectations that most people recover within weeks of a mild injury."
The data was collected in the Waikato region over a year. All potential traumatic brain injury victims were asked to have follow-up assessments. The injuries included, but were not restricted to, sports accidents.
Of the 341 adults who did these assessments, nearly half "continued to experience difficulties with post-concussion symptoms a year after mTBI", and one-tenth experienced difficulties with "cognitive and global functioning".
While not specifically relating to sport, the study adds to the growing evidence that head injuries received in sports like rugby can lead to long-term cognitive issues.
Last month, the Herald highlighted the plight of the 1964 Taranaki Ranfurly Shield squad, five of whom either died with, or are suffering from, dementia.
Other former All Blacks whose dementia was highlighted included the great flanker Waka Nathan, Geoff Old, Greg Rowlands, Mac Herewini, Graham Williams, Tony Steel, Snow White and Sandy McNichol.
While some or several of these players might have been genetically predisposed to dementia conditions such as Alzheimer's disease anyway, says biostatistician Thomas Lumley, the chances or five players from a single team suffering dementia were low enough to reinforce existing concerns about concussion's harmful effects.
Last week, the US-based Journal of Neurotrauma published research suggesting the cognitive challenges faced by former American football players were more likely due to repeated hits to the head - sometimes referred to as sub-concussive blows - than concussion.
Researchers discovered (in an admittedly small sample size) that the number of hits to the head was a better predictor of later-life problems than concussion history.
While celebrating advances on concussion in recent years, Dr Robert Stern, a professor of neurology at Boston University and one of the paper's co-authors, told the Washington Post: "The problem is that the focus on concussion has taken away from an appropriate discussion about the more common subconcussive trauma."
