Several studies have examined the association between head injury and risk of dementia in late-life. Head injury has been shown to increased the risk of cognitive decline, dementia and Alzheimer’s disease [1]. The association may be mediated by the severity of head injury, whether loss of consciousness occurs, the time between head injury and dementia onset and genetic factors [1]. Boxing has also been associated with head injury and a form of dementia (dementia pugilistica), but not with Alzheimer’s disease [2].
Long term follow up of US World War II veterans who were admitted to hospital during service showed that those who had suffered a head injury with loss of consciousness had an increased risk of subsequently developing Alzheimer’s disease compared to those admitted for other reasons. Those with moderate head injuries had 2.3 times the risk and those with severe head injuries had 4.5 times the risk [3].
A meta-analysis of case control studies found a 58% increased risk of Alzheimer’s disease for those with a history of head injury [4]. The association was found to be significant only in males. Males with a history of head injury had 2.3 times the risk of Alzheimer’s, compared to 0.9 times the risk for females with a history of head injury. A possible explanation for the gender difference is the role of female hormones, which may confer a neuroprotective and neuroregenerative effect [4].
Several mechanisms have been proposed to explain the association between head injury and increased dementia risk. Damage to the blood brain barrier, increased oxidative stress, neuronal loss, increased enzyme activity leading to increased beta-amyloid deposition and increased tau pathology have all been implicated [1,2].
References
- Hughes TF, Ganguli M. Modifiable midlife risk factors for late-life cognitive impairment and dementia. Curr Psychiatry Rev, 2009, 5:73-92.
- Woodward M, et al. Dementia risk reduction: the evidence. 2007, Alzheimer’s Australia, Canberra.
- Plassman BL, et al. Documented head injury in early adulthood and risk of Alzheimer’s disease and other dementias. Neurology, 2000, 55:1158-1166.
- Fleminger S, et al. Head injury as a risk factor for Alzheimer’s disease: the evidence 10 years on; a partial replication. J Neurol Neurosurg Psychiatry,2003, 74:857-862.
