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.

“We don’t have brain autopsies, so we don’t know what the underlying biology is,” said the lead author, Dr. Raquel C. Gardner, an assistant professor of neurology at the University of California, San Francisco. “But in Parkinson’s you see abnormal protein accumulation, and there’s some evidence that T.B.I. is linked to deposits of these abnormal proteins.”

In any case, she said, “This study provides the most definitive evidence that there is this association.”