A diagnosis of traumatic brain injury -- whether mild, moderate or severe -- is associated with an increased risk of developing Parkinson's disease as well as a two years younger age at diagnosis, new research in veterans says.
The size of the risk was found to be dependent on the severity of the injury. After a mild injury, usually called a concussion, the increased risk was 56%, but moderate to severe injury raised the risk by 83%, according to the research, published Wednesday in Neurology, the medical journal of the American Academy of Neurology.
Researchers followed veterans for several years to assess Parkinson's risk
A brain injury diagnosis was associated with a 71% increased risk of Parkinson's
Study participants who had been diagnosed with concussion had a 56% increased risk
Parkinson's disease, an incurable neurological disorder, can cause tremors, stiffness and difficulty balancing, walking and coordinating your body's movements.
"Because of the size of the study, this now really provides the highest level of evidence to date that even mild TBI increases risk for Parkinson's disease," said lead study author Dr. Raquel C. Gardner, a neurologist and assistant professor at the University of California, San Francisco. She added that "up to 40% of adults have had a mild traumatic brain injury."
An increased risk
Concussion or mild traumatic brain injury affects an estimated 42 million people worldwide each year, according to research. A recent study suggests that concussion is a growing problem among the elderly.
For the new study, the researchers defined concussion as loss of consciousness from zero to 30 minutes, alteration of consciousness for a moment to 24 hours, or amnesia for zero to 24 hours. Moderate to severe traumatic brain injury was defined as a loss of consciousness for more than 30 minutes, alteration of consciousness for more than 24 hours or amnesia for more than 24 hours.
After searching US Veterans Health Administration databases, the researchers focused on 325,870 veterans who ranged in age from 31 to 65. At the start of the study, none had Parkinson's disease or dementia, though half had been diagnosed with either a mild, moderate or severe traumatic brain injury.
Next, the researchers tracked the veterans to assess the risk of Parkinson's disease.
A total of 1,462 were diagnosed with Parkinson's within 12 years of the start of the study. Among those, 949 (or 0.58% of the total participants) had been diagnosed with traumatic brain injury, while 513 (0.31%) had no history of it.
After accounting for age, health conditions and other factors, the researchers found that veterans with any kind of traumatic brain injury had a 71% increased risk of Parkinson's disease, those with moderate to severe traumatic brain injury had an 83% increased risk, and those with mild traumatic brain injury had a 56% increased risk.
Parkinson's disease was also diagnosed, on average, two years earlier in veterans with a history of traumatic brain injury compared with those unaffected.
Low overall risk
Anthony P. Kontos, research director of the University of Pittsburgh Medical Center's Sports Medicine Concussion Program, said the large number of participants was a strength of the new study.
However, he noted that "a lot of (post-traumatic stress disorder) in this population was probably not accounted for, as it may not have been coded into medical records." The same may be true of alcohol use and other factors that might increase the risk of Parkinson's disease, he said.
"Studies such as this are often misinterpreted to suggest that all military veterans with TBI exposure are condemned to have Parkinson's disease or other negative long-term outcomes," said Kontos, who was not involved in the research.
But this is not accurate. Very few of the veterans, whether they'd had a traumatic brain injury or not, had Parkinson's disease: "no more than three-quarters of 1%," he said.
In fact, just 360 of 76,297 veterans in the study who'd been diagnosed with mild traumatic brain injury developed Parkinson's disease, and 543 of 72,592 veterans once diagnosed with moderate to severe injury developed the disease.
"While all military veterans should seek appropriate care for TBI and be aware of its effects, they should not believe that there is nothing they can do and that everyone has the same outcomes as reported in the current study," Kontos said.
Overall, the findings add to the argument in favor of "timely identification, assessment and treatment" of even mild brain injury in military veterans while highlighting the need for better care and funding for research of this common injury among this at-risk population, he said.
Eating a healthy diet, exercising regularly and controlling medical conditions are the best way to ward off any neurodegenerative disease, Gardner said.
"If anyone is worried," she said, "do a little bit better to live more healthily."