Repeated head injuries among professional football players can lead to hormonal dysfunction and decreased quality of life, according to a study published in the Journal of Neurotrauma earlier this month.

The study found 16 of the 68 retired NFL players examined had pituitary hormonal deficiency. Thirty-four of the former players also showed evidence of metabolic syndrome, a group of conditions that included high blood pressure and high cholesterol that are also associated with low testosterone.

"This is really about quality of life and functioning at an optimal level," said Dr. Daniel Kelly, the study's co-author who is director of the Brain Tumor Center at Saint John's Health Center and the John Wayne Cancer Institute. "If the pituitary gland isn't working well, they don't feel well. They don't think well. It has a real effect on the quality of life."

The retired players ranged in age from 30 to 65 and had median NFL experience of five seasons. Thirty-seven suffered three or more concussions during their careers.

No correlation emerged between the number of concussions and hormonal dysfunction.

"My feeling is the qualification and categorization of concussions is so poor that I think we don't define concussions very well," Kelly said. "This may be the accumulation of many subconcussive impacts every day in practice that these guys have been having every day since high school football."

However, the 16 retired players with hormonal dysfunction did have a higher ratio of concussions to games played than the other players studied.

Kelly worked on the study with Dr. Kevin Guskiewicz, the University of North Carolina professor who is a member of the NFL's Head, Neck and Spine Committee. The NFL, though, had no connection with the study, funded by the National Operating Committee on Standards for Athletic Equipment.

Kelly believes the untreated hormonal dysfunction, which can be treated, could be tied to higher rates of depression among retired players. One study written by Guskiewicz in 2007, for instance, showed retired players who sustained three or more concussions had three times the rate of depression as players with fewer concussions.

"This needs to be studied on a much larger level," Kelly said of the hormonal dysfunction. "I think it's a much more common problem than people realize. I think most of the athletes don't have any idea about this."

nathan.fenno@latimes.com

Twitter: @nathanfenno

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