The Dangers of Later-in-life Concussions

Research links midlife head injury to dementia and Parkinson's

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Published March 21, 2019

While there’s been much recent news about the serious, and detrimental, effects of concussions in youth and professional sports, new studies suggest that even mild concussions in midlife increase vulnerability to dementias and Parkinson’s disease.

How that happens may be due to how a head injury speeds up the buildup of proteins and plaques in the brain.

“We know that Alzheimer’s disease has a long pre-cumulative period. It takes decades to accumulate amyloid and tau [proteins] in the brain until someone shows symptoms,” said Deborah Barnes, a psychiatry professor at the School of Medicine, University of California, San Francisco. She notes that the current thinking also is that more concussions over a lifetime likely equals more dementia risk.

That said, a concussion after a certain age may also prove a midlife tipping point on its own, she notes. “Older adults have less brain reserve, and a head injury can push these people over the line so they express the symptoms of dementia earlier,” Barnes said.

In her own study of more than 300,000 older veterans, published in JAMA Neurology last May, Barnes and her team found that concussion without loss of consciousness led to more than double the risk of dementia. Older veterans who experienced more serious concussions with loss of consciousness increased their risk of dementia nearly four times. (A Barnes study in Neurology last year found a link between mild traumatic brain injury and a 56 percent increase in Parkinson’s in older veterans.)

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If there’s a growing consensus that concussions in midlife can be especially serious, there’s also evidence building that not all bumps on the head are the same. Which part of the brain has been injured, the severity of the injury and whether the injured person is a man or woman all appear as important factors, researchers say.

“There is ample evidence that females appear more vulnerable to concussion because their brains are structurally different than a man’s,” said neurologist David D. Dodick, a professor at Mayo Clinic in Phoenix. “The wires of a woman’s brain are smaller and thinner and more likely to become injured when they’re hit during a concussion.”

A 2017 study in Experimental Neurology backs up this idea. In it, investigators found structural sex differences in rat and human nerve cells, or neurons, which send commands through the brain. Twenty-four hours post-brain injury, parts of the nerve cells, or axons, in females had greater injury compared with male axons. Female axons exhibited significantly more swellings and calcium signaling disruptions.

But the biggest effects from concussions later in life may be from inflammation. Inflammation causes the cell proteins metabolized in the brain to become dysregulated and beta-amyloid and tau, two proteins implicated in Alzheimer’s disease, to be deposited in the brain in an abnormal way, Dodick explains. Inflammation and damage to the brain can continue months to years after the injury, depending on how severe it is, he said.

For all these reasons, “we need to take adult concussions as seriously as we do kids’,” said neurosurgeon Robert C. Cantu, a clinical professor of neurology and neurosurgery at the Boston University School of Medicine. The risk of bleeding in and around the brain is higher in older adults and can be fatal on its own, he added.

To help prevent brain injury, experts suggest that older Americans exercise to improve their balance and prevent falls, and that they follow a “better-safe-than-sorry” approach and seek evaluation after any head injury that could possibly have caused a concussion.

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