Traumatic brain injuries increase the risk of dementia for more than 30 years after a trauma, according to a new study.

However, researchers at Umeå University in Sweden found that the risk of dementia decreases over time.

Traumatic brain injury (TBI) has been associated with dementia, but the details of that risk over time and in different TBI types have not been well studied, according to researchers Anna Nordström and Peter Nordström.

In the new study, they tracked all diagnoses of dementia and TBI in Swedish nationwide databases from 1964 through 2012.

In a retrospective cohort, 164,334 individuals with TBI were matched with control participants who did not have TBI, the researchers said.

In a case-control cohort, 136,233 individuals diagnosed with dementia at follow-up were matched with control participants who did not develop dementia, while in a third cohort, the researchers studied 46,970 sibling pairs where one had a TBI.

In the first year after TBI, the risk of dementia is increased by four- to six-fold, the researchers found.

Thereafter, the risk decreased rapidly, but was still significant more than 30 years after the TBI, according to the study’s findings.

Overall, the risk of dementia diagnosis was increased by about 80 percent during a follow-up period of 15 years.

The risk of dementia was higher for those with a severe TBI or multiple TBIs, the researchers discovered.

The risk factor was similar in men and women, the scientists add.

Because the development of dementia can be a risk factor for accidents resulting in TBI, it’s likely that in some cases, the onset of dementia preceded the TBI, so the researchers caution against making causal inferences.

“The findings of this study suggest an existence of a time- and dose-dependent risk of developing dementia more than 30 years after TBI,” the researchers said in the study, published in PLOS Medicine. “To our knowledge, no previous prospective study with similar power and follow-up time has been reported.”

Source: PLOS

Traumatic Brain Injury Increases Risk of Dementia for Decades After Injury