Links between brain damage and contact sports continue to emerge, with scientists now tying repetitive head impacts to a condition that can lead to Parkinson's disease.

Researchers have already tied repetitive head impacts with the brain disease chronic traumatic encephalopathy (CTE) and dementia. Now, investigators who examined 694 brains after death report ties with Lewy body disease.

Lewy body disease may be behind the motor problems that have been attributed to CTE, said the researchers from Boston University School of Medicine and the VA Boston Healthcare System.

Lewy body disease is associated with thinking, movement and sleep problems, depression and visual hallucinations. It can progress to Parkinson's disease -- a brain disease that affects movement and thinking -- and Lewy body dementia, the study authors explained.

The degree of risk was related to "the number of years an individual was exposed to contact sports, including football, ice hockey and boxing," corresponding author Dr. Thor Stein said in a Boston University news release. He's an assistant professor of pathology and laboratory medicine.

For athletes who played more than eight years of contact sports, the risk was six times higher than for those who played eight years or less, Stein's team found.

The researchers said the link between contact sports and Lewy body disease is independent of CTE.

But the study did find that people with both Lewy body disease and CTE were much more likely to have dementia and symptoms of Parkinson's disease than those with CTE alone.

The findings were published July 25 in the Journal of Neuropathology and Experimental Neurology.

More research is needed to better identify the risks associated with repeated blows to the head and degenerative brain disease, the authors said.