Several epidemiological studies suggest that traumatic brain injury (TBI) is a risk factor for dementia, particularly for Alzheimer’s Disease (AD), although a significant association has not always been observed. Defining the factors that may or may not link TBI to dementia has important considerations given the high incidence of sport and motor vehicle related head injuries in the developed world and the high prevalence of AD in the aged population. Understanding the associations between these two enormous unmet medical needs will have profound implications for post-injury
management as well as for the medico-legal system. Here we review existing studies that support an association between antecedent TBI and increased dementia risk. We review the diverse spectrum of TBI severity and discuss potential mechanisms by which brain injury may trigger a cascade of events that could lead to dementia. We also note the limitations of the current studies and highlight the importance of future research designed specifically to determine whether TBI influences the natural history of AD, particularly with respect to biomarkers.