Risk of dementia may be increased for decades after traumatic brain injury

Written by Roisin Conneely

Researchers from Umeå University (Sweden) have published data indicating that traumatic brain injury (TBI) increases the risk of developing dementia for more than 30 years after the injury, though the risk of dementia decreases over time.
TBI has previously been associated with dementia, but details of the relationship over the time are less well documented.

Anna Nordström and Peter Nordström (Umeå University) tracked diagnosis of dementia and TBI from Swedish national databases between 1964 and 2012, examining a total of 347,537 individuals. A retrospective cohort of 164,334 individuals with TBI were matched with controls who had not experienced a TBI, a further case-control group of 136,233 individuals with a dementia diagnosis at follow-up were matched to participants without the disease and a final cohort examined 46,970 sibling pairs in which one individual had a TBI.

The researchers discovered that, within the first year of a TBI, the risk of dementia is increased by four- to sixfold. Following this period, the risk declines rapidly but is still significant for more than 30 years after the trauma. The overall risk of developing dementia was observed to be approximately 80% higher in those who had experienced a TBI, during an average follow-up period of 15 years.

The risk of dementia was higher for those with severe or multiple experiences of TBI and was similar in both men and women. The findings are complicated by the fact that the development of dementia can be a risk factor for accidents leading to TBI; hence the team cannot definitively claim a causal relationship between the conditions.

The study represents the first major investigation into long-term observations of the relationship between dementia and TBI, as summarized by the authors; “The findings of this study suggest an existence of a time- and dose-dependent risk of developing dementia more than 30 years after TBI. To our knowledge, no previous prospective study with similar power and follow-up time has been reported.”

Source: Nordström A, Nordström P. Traumatic brain injury and the risk of dementia diagnosis: A nationwide cohort study. PLoS Med. doi:10.1371/journal.pmed.1002496 (2018) (Epub ahead of print)