A traumatic brain injury, even a mild concussion, increases the risk for Parkinson’s disease, a new study reports.

Researchers identified all patients diagnosed with T.B.I. in a Veterans Health Administration database — 162,935 men and women — and matched them with the same number of people with similar health and behavioral characteristics but who had not had a brain injury. The study is in Neurology.

Of the T.B.I. cases, half were mild, involving a blow to the head with some subsequent symptoms but with little or no unconsciousness. The rest were moderate to severe, involving extended unconsciousness or long-term symptoms.

After controlling for age, race, income and many medical and psychiatric diseases, they found that compared with those who had had no T.B.I., those with a mild T.B.I. had a 56 percent increased risk for Parkinson’s disease; those with moderate to severe T.B.I. had an 83 percent increased risk.