Concussions and other head injuries in early adulthood may significantly raise the risk of depression decades later, a study of World War II veterans found.
The study has disturbing implications for football and hockey players, motorcyclists and others who have taken blows to the head.
Other research has shown that head trauma patients may be prone to depression shortly after suffering their injuries. But the new findings suggest that the risk persists even 50 years later.
The study involved 1,718 veterans hospitalized for various ailments during the war and questioned 50 years later. About 11 percent who had had head injuries said they currently had major depression, compared with 8.5 percent of those hospitalized during the war for other reasons.
Overall, the lifetime prevalence of major depression was 18.5 percent in the head-injury group and 13.4 percent among the other veterans, Drs. Tracey Holsinger and Brenda Plassman of Duke University and colleagues reported in January's Archives of General Psychiatry.
Plassman said the findings could mean that people who suffer head injuries today - for example, football players or motorcyclists - will have a greater risk of depression. A sizable portion of the veterans who suffered head injuries did so in non-combat situations such as motor vehicle accidents and sports, she said.
The findings underscore the importance of recognizing the potential long-term risks of head injuries so that patients can get early treatment, according to an accompanying editorial.
"The lifelong nature of these disorders argues strongly for their identification and treatment to improve quality of life, and perhaps long-term survival,'' Drs. Robert G. Robinson and Ricardo Jorge of the University of Iowa psychiatry department wrote.
Men with the most severe head injuries - loss of consciousness or amnesia for a day or more - faced a higher risk of developing depression than men with the most mild injuries - those who blacked out or had amnesia for less than 30 minutes, the study found.
While it is unclear how head injury is related to depression, Holsinger and colleagues offer some theories. Depression has been linked with dysfunction in the brain's frontal region, and research has suggested a strong link between depression and head trauma resulting in lesions in the frontal region, the researchers said.
In addition, head trauma causes an inflammatory response that includes increased production of an immune system protein called interleukin 6, and increased levels of interleukin 6 also have been found in depression.
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