CNN  — 

Former NFL star Vincent Jackson, who died in February at the age of 38, was found to have Stage 2 CTE, researchers at the Concussion Legacy Foundation announced on Thursday.

“Vincent Jackson was a brilliant, disciplined, gentle giant whose life began to change in his mid-30s. He became depressed, with progressive memory loss, problem solving difficulties, paranoia, and eventually extreme social isolation,” said Dr. Ann McKee, chief of neuropathology for the VA Boston Healthcare System and director of the BU CTE Center and VA-BU-CLF Brain Bank.

“That his brain showed stage 2 CTE should no longer surprise us; these results have become commonplace. What is surprising is that so many football players have died with CTE and so little is being done to make football, at all levels, safer by limiting the number of repetitive subconcussive hits,” she said.

CTE is a progressive degenerative brain disease caused by repetitive head trauma, according to the Concussion Legacy Foundation. Stage 2 CTE, which can only be diagnosed through an autopsy, is associated with behavioral symptoms like aggression, impulsivity, depression, anxiety, paranoia, substance abuse, and suicidal ideation, along with progressive cognitive symptoms, according to the foundation.

“CTE will not disappear by ignoring it, we need to actively address the risk that football poses to brain health and to support the players who are struggling,” McKee said.

Jackson was found dead in a hotel room on February 15 in Brandon, Florida, with no apparent signs of trauma, officials said. His family had reported him missing less than a week prior, and the case was canceled after finding him and performing a wellness check at the hotel where he had stayed since January, police said.

Following a standout collegiate career at the University of Northern Colorado, Jackson was drafted by the San Diego Chargers, now based in Los Angeles, in 2005 and played seven seasons there before moving on to the Tampa Bay Buccaneers, where he played the last five seasons of his 12-year career.

Jackson was a three-time Pro Bowl selection and was nominated four times for the Walter Payton Man of the Year award, which recognizes players who have had a positive impact on their community, according to the Buccaneers.