Retired boxers appear to have a greater risk than other people do of developing degenerative brain disorders such as Alzheimer's and Parkinson's diseases decades after they leave the ring, doctors said Friday.

In a study conducted at Thomas Jefferson University in Philadelphia, the doctors evaluated eight retired boxers, between the ages of 69 and 86, with symptoms of an unexplained mental decline.The former fighters had no observable neurological problems when they retired from the ring and held responsible jobs until their later years when all were diagnosed with Alzheimer's disease. Three also had Parkinson's disease.

Several of the boxers in the study also displayed an abnormal increase in the amount of cerebrospinal fluid in the skull and irregular heartbeats, the doctors said.

"While our study was small and some of the data has yet to be analyzed, our findings indicate that the type of chronic head injuries boxers suffer during their careers could lead to delayed and selected degeneration of the central nervous sytem in susceptible individuals," said Dr. Patricio Reyes, associate professor of neurology at Thomas Jefferson.

A few years after he retired in 1980, former world heavy weight champion Muhammad Ali's speech became slurred and he seemed confused during public appearances. His doctors diagnosed the ailment as Parkinson's disease.