By Dan Whitcomb

LOS ANGELES (Reuters) - Tissue from the brain of former San Diego Chargers star Junior Seau, who committed suicide in May, has been sent to the National Institutes of Health for study amid growing concerns over the long-term effects of football-related head injuries.

The brain sample was sent to the NIH, the U.S. government's primary biomedical research institution, at the request of Seau's family members, said Sarah Gordon, spokeswoman for the San Diego County Medical Examiner's office.

Gordon declined to comment further on the decision. The family's pastor has previously said family members were considering having Seau's brain studied for evidence of football-related injuries.

Seau, a 20-year National Football League veteran and fan favorite widely regarded as one of the best defensive players of his generation, shot himself in the chest on May 2. He left no suicide note.

His death at age 43 came during heightened scrutiny of the effects of repeated blows to the head in football, ice hockey and other contact sports and the potential for such injuries to contribute to depression and other health problems in players.

It also marked at least the third suicide by a former NFL player since February 2011, when ex-Chicago Bears defensive back Dave Duerson, 50, killed himself with a gunshot to the chest after complaining of headaches, blurred vision and memory loss.

Duerson left a note with the request: "Please, see that my brain is given to the NFL's brain bank."

More than 2,000 former NFL players and spouses have sued the league, saying it deliberately concealed the risk of brain damage from repeated blows to the head suffered by players.

The NFL has called the suit groundless, saying that it has long made player safety a priority and calling attention to its benefits programs for former players.

The league has focused in recent seasons on health and safety issues. It has cracked down on hits to the head and stiffened rules that bar players from using their helmets as a weapon through head-first contact, which is subject to fines and suspension for repeat offenders.

Despite the high-profile suicides, a study published in January by a division of the U.S. Centers for Disease Control and Prevention showed retired NFL players had a lower rate of suicide than the general public.

A spokesman for NIH's National Institute of Neurological Disorders and Stroke could not immediately be reached for comment.

(Reporting by Dan Whitcomb; Editing by Cynthia Johnston and Todd Eastham)