NFL players have a greater chance of developing depression as they age, according to new research.

Two studies, which will be presented at the American Academy of Neurology's 65th Annual Meeting in San Diego, March 2013, found that professional football players are at greater risk of depression because of brain damage caused by concussions.

According to the U.S. Centers for Disease Control and prevention, about 1.6 to 3.8 million sport concussions happen each year. Researchers say that while it is known that sports concussions can cause immediate disturbances in mood and thinking, there has been little research on the long-term effects of concussions that may emerge later in life.

"Our study shows that athletes who have sustained concussions in early adulthood may be at a higher risk for developing depression as they age compared to the general population," study author Nyaz Didehbani of the Center for BrainHealth at The University of Texas at Dallas said in a statement.

"It is important when a concussive experience occurs that medical professionals appropriately include depression screening in their follow-up assessment. Depression is a treatable condition if the proper and necessary steps are taken," Didehbani said.

Researchers in the first study compared 34 retired NFL athletes with a history of concussion to 29 people of the same age from the general population with no concussion history. Researchers found that athletes who had greater symptoms of depression scored significantly higher than the minimal range for depressive symptoms. Researchers said that because the retired athletes included in the study had on average four concussions in the past, the recent findings reinforce the link between depression scores and the number of lifetime concussions.

In the second study, researchers studied 26 retired NFL athletes. Of all the participants, five had depression and 21 did not have depression. Using MRI scans, researchers were able to measure damage to white matter in the brains of participants.

Researchers explained that white matter contains tissue and nerve fibers that help transmit signals from one part of the brain to another, and damage to white matter from traumatic brain injury has previously been seen in some patients with depression.

Researchers found that they could accurately predict which former players had depression with 100 percent sensitivity and 95 percent specificity just by looking at the amount of white matter damage in one area of the brain.

Sensitivity is a measure of actual positives that are correctly identified as positive and specificity is a measure of negatives that are correctly identified.

In the second study, researchers found that the severity of depressive symptoms correlated with the degree of white matter damage in the brain.

"Aside from providing important insights into the nature of depression as it relates to brain damage in retired NFL athletes who have been exposed to concussive and repetitive head injuries, this study also may help us to understand the similar behavioral symptoms seen in other sports-related head injuries and in combat-related blast injuries seen in armed service members," researcher Dr. Kyle Womack of the University of Texas Southwestern Medical Center in Dallas said in a statement.

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