Head injuries can increase the risk of dementia
A history of a serious head injury is associated with an increased risk of dementia. On average, if you have suffered a head injury where you lost consciousness, you have a slightly higher risk of developing dementia. But this doesn’t mean you will definitely get dementia.
Increased enzyme activity and other brain changes after a head injury might contribute to the increased risk of dementia.
What’s the evidence that head injury increases dementia risk?
Several studies have shown that those with a history of head injury have on average a higher risk of developing dementia, compared to those who have not had a head injury. This has been found for serious head injuries involving loss of consciousness.
Studies of World War II veterans found that those who suffered severe head injuries were over 4 times more likely to develop dementia. Boxing has been associated with brain damage and a particular form of dementia.
A review of this research found that there is around a 50% increase in dementia risk in those with a history of head injury (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).
Interestingly, the effect seems to be only significant in men. When men were studied separately, those with a history of head injury were found to have more than twice the risk of dementia. Women with a history of head injury did not have an increased dementia risk.
Evidence rating for head injury 
Many observational studies have shown that serious head injury increases dementia risk and the association has also been established in meta-analyses combining results from several studies. So, avoiding head injury can help avoid an increased risk of developing dementia.
How does head injury increase dementia risk?
There are several ways in which head injury might contribute to the development of dementia. For instance, after head injury there is increased enzyme activity, and this may increase the production of the brain ‘plaques’ that are found in Alzheimer’s disease.
A possible explanation for the gender difference in the risk of dementia following head injury is a protective effect of the female hormones, oestrogen and progesterone.
