Having a single concussion may increase a person's risk for Parkinson's disease, a new study suggests — but the overall risk of developing the disease still remains low.
The study, which analyzed information from more than 320,000 U.S. veterans, found that those who'd experienced a mild traumatic brain injury (TBI), often called a concussion, were 56 percent more likely to be diagnosed with Parkinson's than those who'd never had a concussion.
Although the study participants had served in the military, their concussions were often reported to have happened during their civilian lives, said senior study author Dr. Kristine Yaffe, a professor of psychiatry, neurology and epidemiology at the University of California, San Francisco (UCSF) School of Medicine. "As such, we believe [the study] has important implications for the general population," Yaffe said in a statement.
Previous research has found a link between Parkinson's disease and moderate to severe TBIs; however, this is the first large study to show a link between milder head injuries and Parkinson's, the researchers said.
However, it's important to note that, even if participants experienced a concussion, their risk of Parkinson's was still very low. Overall, 360 out of 76,297 participants with a concussion, or 0.47 percent, developed Parkinson's; and 543 out of 72,592 participants with moderate to severe TBIs, or 0.75 percent, developed the disease.
Why is there a link?
The researchers analyzed health information from 325,870 veterans, ages 31 to 65, using three U.S. databases from the Veterans Health Administration. About half of the participants had been diagnosed with either a concussion or a more serious moderate to severe TBI at some point in their lives. Participants were then followed for an average of 4.6 years.
During the follow-up time, 1,462 participants were diagnosed with Parkinson's. Of these, 949 participants with any TBI, or 0.58 percent, developed the disease, compared with 513 participants with no TBI, or 0.31 percent.
The risk of Parkinson's was higher for those who'd had a moderate to severe TBI. These participants were 83 percent more likely to develop the condition than those who'd never had a TBI.
It's not clear exactly why head injuries are linked with an increased risk of Parkinson's. But generally, head injuries can cause inflammation in the brain, which may lead to changes in cells and brain structures that contribute to Parkinson's, Dr. Barbara Changizi, a neurologist at The Ohio State University Wexner Medical Center, told Live Science in a 2016 interview. A person's genetics may play a role as well, Changizi said.
Some studies have also found abnormal brain deposits of a protein called alpha-synuclein, which is a hallmark of Parkinson's, in people with traumatic brain injuries, the authors of the new study said.
The study "highlights the importance of concussion prevention, long-term follow-up of those with concussion, and the need for future studies" to investigate the mechanisms behind the link, as well as factors that might reduce the risk of Parkinson's after a concussion, said lead study author Dr. Raquel Gardner, an assistant professor of neurology at the UCSF School of Medicine.
The study was published April 18 in the journal Neurology.
Original article on Live Science.