A traumatic brain injury doesn’t just raise your risk of later neurological disorders; preexisting neurological disorders may raise the risk of brain injury, concludes a recent 2026 study from the San Francisco Veterans Affairs Health Care System.

Published June 17, 2026. in the journal Neurology, the Department of Defense-supported study tracked more than 55,000 older veterans. Scientists found that traumatic brain injury was tied to higher rates of stroke, dementia, epilepsy, and Parkinson’s disease both before and after the injury. “Our findings raise the possibility that… [pre-existing brain diseases] are themselves risk factors for TBI in older people,” said study author Carrie Peltz, PhD, of the San Francisco Veterans Affairs Health Care System.

In the year before a TBI, older veterans were about three times more likely to have been diagnosed with stroke, dementia, or Parkinson’s and more than four times more likely to have epilepsy. After a TBI, they were roughly twice as likely to have a stroke or epilepsy. This results greatly build on an Oxford Academic, PubMed-accessible, 2025 study that found, “Among those with TBI, patients with pre-injury dementia had particularly high chronic mortality.” While causality has not firmly been medically defined, the study’s results are clear.