Compared to participants who never experienced a head injury, a history of a single prior head injury was associated with a 1.25 times increased risk of dementia.
According to results from the prospective Atherosclerosis Risk in Communities (ARIC) study, head injury is associated with an increased risk of dementia in a dose-dependent manner, with stronger associations found among females and White participants.1,2
There were 2350 incident dementia cases, 1620 of which were among persons without head injury and 730 among those with had a history of head injury, occurring over 320,306 person-years (PYs) of follow-up that were observed in the study. The crude incidence rate for dementia per 1000 PYs was 6.2 (95% CI, 5.9-6.5) among persons without head injury and was 12.5 (95% CI, 11.7-13.5) among persons with head injury.
Over a median of 25 years in adjusted models, head injury was associated with a 1.44 (95% CI, 1.32-1.57) times increased risk for incident dementia. Notably, this association remained significant (hazard risk [HR], 1.32; 95% CI, 1.21-1.44) after further adjustment for hospitalized depression and post-traumatic stress disorder (PTSD).
“Head injury is a significant risk factor for dementia, but it’s one that can be prevented. Our findings show that the number of head injuries matter—more head injuries are associated with greater risk for dementia,” lead investigator Andrea L Schneider, MD, PhD, assistant professor of neurology, University of Pennsylvania, said in a statement. “The dose-dependence of this association suggests that prevention of head injury could mitigate some risk of dementia later in life. While head injury is not the only risk factor for dementia, it is one risk factor for dementia that is modifiable by behavior changes such as wearing helmets and seat belts.”
Of the 3440 with head injury, 2620 had 1 head injury, and 820 had 2 or more head injuries, occurring either before study baseline or by the end of follow-up. Patients who had 1 head injury were associated with a 1.25 (95% CI, 1.13-1.39) times increased risk, whereas those who had 2 or more head injuries were associated with a 2.14 (95% CI, 1.86-2.46) times increased risk of incident dementia compared to those with no head injury.
Schneider and colleagues also found evidence for a stronger association of head injury with incident dementia among females (HR, 1.09; 95% CI, 1.51-1.90) compared to males (HR, 1.15; 95% CI, 1.00-1.32; P <.001). There was also a stronger association of head injury with incident dementia among White participants (HR, 1.55; 95% CI, 1.40-1.72) than among Black participants (HR, 1.22; 95% CI, 1.02-1.45; P <.001).
In models that accounted for the competing risk of death, the magnitude of the association between head injury and incident dementia was stronger (HR, 1.72; 95% CI, 1.57-1.89). Additionally, the population attributable risk of head injury on dementia risk was 9.5% (95% CI, 7.5-11.4).
“Given the strong association of head injury with dementia, there is an important need for future research focused on prevention and intervention strategies aimed at reducing dementia after head injury,” Schneider added. “The results of this study have already led to several ongoing research projects, including efforts to uncover the causes of head injury-related dementia as well as investigations into reasons underlying the observed sex and race differences in the risk of dementia associated with head injury.”