The first symptoms of a head injury such as confusion, memory loss and changes in speech and vision can resemble those seen in dementia.

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Depending on how severe the injury is, such symptoms may resolve quickly, last a long time or never completely go away.

The symptoms that arise immediately after a head injury do not generally worsen like they do in cases of Alzheimer’s disease. However, certain types of head injuries can increase the risk of Alzheimer’s or other forms of dementia developing later in life.

Factors that appear to influence this risk include age at the time of the brain injury and injury severity.

Severe head injuries may increase the risk for Alzheimer’s more than mild ones do and sustaining an injury at an older age may also add to the risk. Also, repeated mild injuries can affect cognitive ability in the future.

The younger the person is, the greater the dementia risk

A study published in The Lancet in April 2018 was one of the largest of its kind to look at the link between dementia risk and traumatic brain injury (TBI). A TBI is defined as any head injury that disrupts brain function brain, with leading examples including motor vehicle accidents, assaults, and falls. A concussion is classified as a mild TBI.

After studying the link between TBI and cognitive decline, the Danish and US researchers concluded that the younger a person is at the time of the injury, the greater their risk of developing Alzheimer’s and other forms of dementia.

Their analysis of health records available for 2.8 million people aged over 36 years, revealed that individuals who had a TBI in their 20s were at a 63% greater risk of developing dementia over the next thirty years, compared with people who had no such injury.  However, if the injury was sustained when they were in their thirties, this risk only increased by 37%.

Study author and behavioral scientists Jesse Fann (University of Washington School of Medicine) says the study raises some important questions, particularly whether efforts to prevent TBI, especially among young people, are adequate, given the huge and growing burden of dementia and the prevalence of TBI worldwide.

In total, 5.3% of participants with a history of TBI had dementia, compared with 4.7% among those with no TBI history. The dementia risk increased the greater the number and severity of the TBIs sustained and even just one mild TBI (concussion) was linked with a 17% greater risk of dementia.

Although 85% of the TBIs were classified as mild, the researchers said they were still likely to have been fairly serious concussions, since the symptoms were severe or persistent enough to require a hospital visit.

The study also looked at the effect that sustaining multiple separate TBIs had on dementia risk. They found that a person who had sustained one TBI was at a 22% greater risk of developing dementia after the age of 50, compared with someone who had never sustained a TBI. For someone who had sustained two injuries, this risk increased by 33% and for five or more TBIs, the risk rose by 200%.

Commenting on the study, researchers Mahmoud Maina from the University of Sussex said the findings are “truly novel due to the large sample size employed, in-depth history collected and follow-ups.”

Jonathan Schott from University College London’s Institute of Neurology said the research perhaps provides the best evidence yet that traumatic brain injury is a risk factor for dementia. However, further research is required to differentiate the types of injuries (e.g. sports-related concussion) and how they affect the brain, he added. “These uncertainties notwithstanding, this study reinforces the importance of trying to prevent injury to the brain.”

A concussion can raise dementia risk even if there is no loss of consciousness

Another study published in May 2018 in JAMA Neurology suggested that concussion can increase dementia risk, even if has not caused a loss of consciousness.

Led by a team at the University of California (UCSF), the study, which included more than 350,000 US war veterans, showed that concussion without loss of consciousness was associated with a 2.4-fold increased risk for dementia.

Among those who did lose consciousness, the risk was 2.5 times higher and for those who had sustained more serious moderate-to-severe traumatic brain injuries, the risk was 3.8 times higher.

Chief Policy and Research Officer at Alzheimer’s Society, Doug Brown, said that for some time dementia researchers have been fascinated by the potential link between head injuries such as concussion and the risk of developing dementia.

He points out that although JAMA Neurology study was one of the largest studies of its kind, it did only focus on US war veterans, so it is not yet clear how applicable the findings are to the public, so we do not know how relevant it is to the general public yet. more detailed studies of a wider population group would be needed to investigate and confirm the possibility that concussion doubles a person’s dementia risk.

Written by

Sally Robertson

Sally has a Bachelor's Degree in Biomedical Sciences (B.Sc.). She is a specialist in reviewing and summarising the latest findings across all areas of medicine covered in major, high-impact, world-leading international medical journals, international press conferences and bulletins from governmental agencies and regulatory bodies. At News-Medical, Sally generates daily news features, life science articles and interview coverage.