Contact sports increase Parkinson's disease risk

Injuries from playing contact sports, such as rugby, boxing, and martial arts, have been linked to a heightened risk of dementia. A new study now says that contact sports may actually lead to other neurodegenerative diseases, and it explains why.

At Medical News Today, we have covered studies linking brain injury — usually as a result of playing contact sports — with a higher risk of developing various conditions later in life.

One such study argued that brain injuries could accelerate the processes that bring about Alzheimer's disease, which is the most common type of dementia.

It is characterized most prominently by memory loss, a sense of disorientation, and an impaired ability to carry on a daily routine.

Numerous studies during the past few years have suggested that repeated head injuries obtained from participation in contact sports are linked to chronic traumatic encephalopathy (CTE), which is a degenerative brain disease that can lead to dementia.

Now, a study led by researchers from the Boston University School of Medicine in Massachusetts has found that people engaging in contact sports may also be more likely to develop Lewy body disease.

In that condition, a protein called alpha-synuclein forms abnormal deposits known as Lewy bodies in the brain. Lewy body disease is associated with dementia symptoms, as well as with Parkinson's disease.

Traditionally, scientists have believed that the motor symptoms — such as tremors, slowness of movement, and difficulty walking — experienced by some athletes are attributable to CTE.

However, the researchers argue instead that those symptoms are actually a byproduct of Lewy body disease, independently of CTE.

"We found the number of years an individual was exposed to contact sports, including football, ice hockey, and boxing, was associated with the development of neocortical [Lewy body disease], and Lewy body disease, in turn, was associated with Parkinsonism and dementia," says study author Dr. Thor Stein.

The researchers' findings are now published in the Journal of Neuropathology and Experimental Neurology.

Risk increased in long-term sports players

Dr. Stein and team drew their conclusions after studying 694 donated brains from three sources: the Veteran's Affairs-Boston University-Concussion Legacy FoundationBrain Bank, Boston University Alzheimer's Disease Center, and the Framingham Heart Study.

They found that the total number of years that a person had spent playing contact sports was associated with an increased risk of developing Lewy bodies in the cerebral cortex.

People who participated in contact sports for over 8 years had the greatest risk of developing Lewy body disease — six times higher, in fact, than the increase in risk seen in people who had played contact sports for 8 years or under.

Moreover, people who had both CTE and Lewy body disease had a higher risk of dementia and Parkinson's than those who only had CTE.

These findings may not be surprising. After all, as the authors note, previous research had already shown that the number of years spent playing contact sports can be used to predict the severity of dementia-related pathology, as well as the severity of CTE in former players.

This research, the scientists add, builds on data provided by existing studies, though further efforts should be made to ascertain, with more exactitude, the health risks to which repeated brain injuries expose athletes.

"Future studies incorporating more participants with neocortical [Lewy body disease] and contact sports play will be necessary to more accurately determine the best threshold and risk of contact sports participation," the researchers write.