The immediate effects of a head injury can include symptoms that are also seen in dementia, such as confusion and memory loss, as well as changes in speech, vision and personality. Depending on the severity of your injury, these symptoms may clear up quickly, last a long time or never go away completely.
However, such symptoms that begin soon after your injury generally don't get worse over time as happens with Alzheimer's disease.
Certain types of head injuries, however, may increase your risk of developing Alzheimer's disease or other types of dementias later in life. The factors that seem to affect your risk include your age at the time of the injury and the severity of the injury.
More-severe head injuries may increase your risk of developing Alzheimer's disease. And sustaining a head injury when you're older, around age 55, may also increase your risk. Repeated mild injuries also may increase your risk of future problems with thinking and reasoning.
You're likely at greatest risk of developing dementia or Alzheimer's later in life, post-head injury, if you also have other risk factors. For example, carrying one form of the apolipoprotein E (APOE) gene increases the risk of Alzheimer's in any individual.
It's important to note that many people who sustain a severe head injury never develop Alzheimer's disease or later dementia. More research is needed to understand the link.