A nationwide study of traumatic brain injuries (TBI) in Finland has found that being hospitalized with a moderate to severe TBI as an adult increases the risk of dementia later in life.

Why it matters: Traumatic brain injury is a leading cause of death and injury globally. In 2013, 2.8 million Americans went to the emergency room, were hospitalized or died from a traumatic brain injury, according to the CDC. As populations age, it's important to know the long-term consequences of brain injuries. The authors believe this is the first nationwide survey of TBI and neurodegenerative disease.

What they did: The researchers used data from the Finnish Care Register for Health Care to identify 19,936 18-65 year olds who were hospitalized with a moderate-severe TBI and 20,703 persons hospitalized with mild TBI between 1987 and 2014. They looked for a diagnosis of neurodegenerative disease starting one year later. Since past research has shown that mild traumatic brain injuries are not associated with dementia, the group with mild TBI's were used to control for socioeconomic status. The research was published Wednesday in the journal PLOS Medicine.

What they found: People hospitalized with moderate to severe traumatic brain injury are 90% more likely to develop dementia than those with a mild TBI, even after controlling for socioeconomic status, which is a risk factor for both TBI and neurodegenerative disease. There was no increase in risk of Parkinson disease or amyotrophic lateral sclerosis (ALS).

Limitations:

The study only looked at people who were hospitalized, so some mild cases of TBI may not be included in the study. However, the large sample size helps to control for some potential sources of error. It's also possible that the same factors that make someone likely to develop dementia may make them more likely to receive a traumatic brain injury.