People with a history of concussion may face increased risks of certain psychological and neurological conditions, a large new study suggests.
The study of more than 186,000 Canadians found that those who suffered a concussion were more likely to develop any of several conditions, including: attention-deficit/hyperactivity disorder (ADHD); depression or anxiety; Parkinson's disease; or dementia.
Their risks were roughly 40% to 70% higher, compared to people who did not sustain a concussion during the 25-year study period.
The researchers stressed that the vast majority of people in the study -- concussed or not -- did not develop Parkinson's, dementia or ADHD. Depression and anxiety disorders were more common across the board, with a higher prevalence in the concussion group.
"We're not trying to scare people or have parents keep their kids out of sports," said lead researcher Marc Morissette of the Pan Am Clinic Foundation in Winnipeg, Manitoba.
Beyond that, the findings do not necessarily mean that concussions, per se, were to blame, said Dr. Sean Rose.
Rose, who is co-director of the Complex Concussion Clinic at Nationwide Children's Hospital in Columbus, Ohio, was not involved in the study.
He said research like this can point to a correlation between concussion and later disease risks -- but cannot prove cause and effect.
It's difficult, Rose said, to account for all the other variables that could contribute to conditions like depression or dementia. And in this study, he noted, one question is: What were people's medical diagnoses before their concussion happened?
Dr. Barry Kosofsky is a pediatric neurologist at Weill Cornell Medicine and NewYork-Presbyterian in New York City. He agreed the findings do not prove a cause-and-effect connection.
But, he said, the key point still stands: People with a history of concussion faced heightened risks of these five conditions, for whatever reason.
"The findings are provocative," said Kosofsky, who reviewed the results.
The study, published online July 27 in Family Medicine and Community Health, looks at an issue that is drawing growing attention: What are the long-term consequences of a blow to the head -- especially repeated ones?
There has been particular concern about sports-related concussions in young people. While the concussion rate in youth sports remains fairly low, lots of kids play sports. In 2017, 2.5 million U.S. high school students said they'd had at least one concussion related to sports or recreation in the past year, according to the U.S. Centers for Disease Control and Prevention.
Concussion is a mild form of traumatic brain injury. Common symptoms include headache, ringing in the ears, nausea, vomiting, fatigue and blurry vision.
The good news, Rose said, is that with a proper balance of rest and activity, most kids with a concussion recover within a couple of weeks.
As for longer-term consequences, researchers don't have all the answers. In this study, Morissette's team found that ADHD was more commonly diagnosed in people who'd sustained a concussion -- with their risk being 39% higher than the comparison group. On average, ADHD was diagnosed at age 17.
Some past research, though, has suggested kids with ADHD have a higher concussion risk -- so the exact nature of the relationship between the conditions is uncertain.
To Kosofsky, the findings on the other conditions were more interesting. When it came to Parkinson's disease, for instance, adults with more than three concussions were at three-times greater risk than those with one concussion.
That kind of "dose-response" correlation, Kosofsky said, lends strength to the finding.
But it's still difficult to know what is happening, he said. For example, could people in the early stages of Parkinson's -- which involves movement and balance impairments -- be at greater risk of concussion?
The findings are based on 25 years' worth of health insurance claims and other medical data on Manitoba residents. During that time, almost 47,500 people were diagnosed with a concussion. Each was compared to three concussion-free people of the same age and sex.
On average, the concussion group was about 60% to 70% more likely to be diagnosed with depression/anxiety, Parkinson's or dementia. The link between concussion and depression/anxiety was stronger among women than men, though it's not clear why, according to Morissette.
While the study looked at a 25-year period, Morissette said it cannot show whether concussions at a young age are associated with risks for diseases that normally appear decades later -- like Parkinson's and dementia.
Rose said his advice to parents is to learn the signs and symptoms of concussion, and if their child develops any of them, see a doctor.
As for sports, Kosofsky said physical activity is good for kids, but certain sports are riskier than others when it comes to concussion. Some of the riskiest include football, boxing, wrestling, lacrosse and hockey, he added.
The U.S. Centers for Disease Control and Prevention has an overview on concussion.